Psych homework

Hello, Welcome to another Psychology 100 Online Lecture. This lecture is optional for you this week (but very highly recommended) because much of the same material is covered in the chapters of your textbook on biological foundations of psychology. I am including it because I have found that these topics are difficult for many students and I remember when I was a student, if there were topics that I was not understanding, it often helped to read the same ideas explained by another author. So, I am offering the following lecture to you as an optional supplement to what is in the chapters of your textbook on biological foundations to help you better grasp these ideas, and to help you prepare for the coming midterm. Experience has shown me that without this lecture, students are at a real disadvantage when it comes to grasping these technical topics and doing well on the Midterm exam. Enjoy.

If you do read the lecture below (and I highly recommend that you do), please post here, letting me know that you have read the lecture. It will help you master the material on biological foundations for the coming midterm. This lecture will be posted again next week and it will be required then, so here's a chance to get ahead on next week's assignments.

BIOLOGICAL FOUNDATIONS OF MIND AND BEHAVIOR

by Ken Koenigshofer, Ph.D.

Copyright 2004 (revised 2012). All rights reserved.

This lecture considers biological foundations of the mind and behavior. The biological foundations of the mind and behavior include several topics:

1. evolution

2. genetics

3. brain and nervous system anatomy

4. brain and nervous system functions

5. nerve cell (neuron) structure and function

6. communication betweeen neurons (synaptic transmission)

7. psychoactive drugs and their mechanisms of action (how the drugs act upon neurons and their activity)

Recall from your textbook the discussion about mind-body dualism vs. materialism. Mind-body dualism, an idea first discussed by the French philosopher Rene Descartes, is the belief that the mind is non-material or non-physical and that mental events (such as thoughts, memories and feelings) are independent of the physical body (and brain). Materialism, by contrast, is the view that everything in the universe, including the mind, is really physical or material, being entirely composed of matter and energy. (Note that energy is a form of matter. Experiments in physics show that even light and other forms of electromagnetic energy actually have mass or weight indicating that they are material).

The scientific view of the universe is materialism, the entire universe is thought to be composed of matter and energy alone. The scientific view of the mind, therefore, is that it also is material. On this view, mental events are entirely dependent upon physical events in an entirely physical brain. What is the structure of this physical organ and how does it function to produce mind and behavior? (Topics 3 and 4 listed above). What is the brain composed of, what features do those cells have, and how do those cells function to produce behavior and mental events? (Topics 5 and 6 above). What physical interventions affecting brain function can alter consciousness (the mind) and how do those physical interventions on brain function work at the cellular level? (Topic 7 above).

The first topic, evolution, has to do with origins, specifically with the origins of the organization of living things. TAKE A LOOK AT THIS WEBSITE ON EVOLUTION:http://www.pbs.org/wgbh/evolution/

The universe is a fairly orderly place. There are patterns and regularities in the universe at almost every level from the subatomic to the development of stars and galaxies. It is the job of science to discover and describe regularities in nature and then to use these laws to make predictions. Several centuries ago, the regularities in the motions of the planets became explicable to us when early astronomers discovered basic laws of motion and laid the foundations for the future development of physics.

Like other aspects of our universe, human and animal minds, behaviors, and the brains that underlie mental events and action are all highly organized. The organization here, however, is the product of laws beyond the laws of physics alone. The laws of life, of living things, are also operating here. Afterall, the mind, the brain, and behavior are all aspects of living organisms.

Human and animal minds, human and animal behaviors, human and animal brains are all orderly and well structured, to function in ways that sustain survival and reproduction. Scientists believe that this orderliness in living things is the product of the basic law of life; that basic law of life is evolution by means of natural selection (to be discussed below).

For example, flying in flies involves a very complex, and precisely coordinated set of movements. How do flies organize these movements? How do they know what to do? Why don’t they fly upside down, or crash headfirst into the ground?

Spiders building a web, or bees constructing a hive, also engage in complex, precisely organized sets of movements. The web building behavior of spiders is so precisely organized that people who know about spiders can tell the species of spider from the construction of its web alone, even if the spider isn’t present. How do spiders and bees know what to do and precisely how to do it?

Desert ants leave their nests zigzagging in search of food. When they find some, they navigate nearly in a straight line back to their nests. How do they know how to perform this precise navigation? In fact, how do they even know that they should return to their nest at all? What makes them do so?

Trigger fish find a hole in a coral reef, occupy it, and then defend it vigorously against other trigger fish, first by making warning noises, and then by a savage attack if the intruder does not heed the warning sounds. How does this behavior, and all of the movements which compose it, become organized? How does the fish know what to do and how to do it?

Sea turtles in Kona, Hawaii (one of my favorite places) graze on coral reefs; so do many of the colorful tropical fish there. How do they know what to eat and what to avoid?

Lions live in groups called prides and maintain hunting territories which they pass from one generation to the next. How do they know to do this? How do they know to engage in hunting behavior, what to hunt, and how to hunt?

Human beings, the world over, engage in acquisition and use of language, have emotions that lead to reproductive activity (courtship and sex), and prefer fats and sweets in their diets. Why?

How is the orderliness, the structure, in human and animal behavior produced and perfected so that animals and humans do the "right" things (behaviors that are adaptive) at the "right" times? How is this organization, this structure, produced and how is it transmitted over generations? These are issues addressed in Topics 1 and 2 listed above. We take up these issues first.

Evolution

Matter in the universe is not randomly distributed throughout space. Instead it becomes organized into structures such as stars and planets and the features that these possess. This organization of matter is produced by the laws of physics.

At least one planet has developed living organisms. Organisms are very highly organized matter and this organization is of a very specific sort. The additional organization that characterizes living things is the product of laws of life (the laws of evolution) acting in addition to the laws of physics. Evolution by natural selection is, according to modern scientific views, the origin of the orderliness within living things.

How does behavior become organized? The same processes which have ordered the anatomy and physiology of a species are involved in the organization of the behaviors and mental processes characteristic of that species. In other words, evolution by natural selection is the force which organizes the anatomy, physiology, and the behavioral adaptations of organisms. What is evolution? How does evolution work?

The basic proposition of all theories of evolution is that species change over time. Charles Darwin called it "descent with modification." Viewed from the standpoint of modern genetics, evolution involves changes in the frequencies of various genes in a population of organisms. Changes in gene frequencies in a population over time are correlated with changes, over generations, in the frequencies with which various traits occur in the members of a species. That is, over generations, the proportion of individuals of a species which possess a particular trait may increase or decrease, even to the point where most members of the species come to possess a new trait or, alternatively, most no longer possess a trait which was once characteristic of that species in its evolutionary past. For example, some of the primate ancestor species from which we evolved had tails. This trait has decreased in frequency in humans to the extent that it is no longer characteristic of us as a species, however, occasionally, a human baby is born with a tail-like structure coming from the base of its spine. (In such cases, the doctor just cuts it off without complications and the incident may be quickly and thankfully forgotten). The point is, that a trait, once found in most members of a species, decreased in frequency to the point where it has nearly disappeared in a new related species, us. But even so, it can still appear, although in modified form and with a very low frequency. Other traits such as the human "opposable" thumb, permitting the precision grasping and manipulation of objects, have increased in frequency to the point where they have become a universal characteristic of the species. What is the mechanism that changes gene frequencies and thus directs the paths which evolution follows?

According to Darwin’s theory of natural selection, if some traits increase the chances of survival and reproduction, then the individuals that possess those traits will naturally survive, and thus reproduce, in larger numbers. Therefore, those traits, and the genes that underlie those traits, will tend to be reproduced often and thus increase in frequency in the population. Other traits which impair chances of survival and reproduction will tend to be weeded out of the population because the individuals which possess those unfavorable traits are at a survival (and thus reproductive) disadvantage. These individuals with traits making them less well adapted to their environments will tend to die before they have a chance to reproduce or for other reasons will reproduce less frequently. Thus, these individuals as well as the less well adapted traits which they carry (and the genes that code those traits) tend to be eliminated from the population. The result is a change in gene frequencies, and the frequencies of various traits (anatomical, physiological, or behavioral), such that those which are favorable (adaptive) get preserved over generations, and those which are harmful (maladaptive) or less adaptive get weeded out of the species. This process of natural selection has been called "survival of the fittest", but actually, it is more accurately "reproduction by the fittest" leading to the preservation of adaptive traits and the elimination of those traits which are less adaptive in a particular environment. Repetition of this process over many generations refines the traits (the adaptations) of a species (and the genes that underlie those traits), "perfecting" the species for exquisitely effective adaptation to its environment. Notice that what determines whether any particular trait is a favorable one or an unfavorable one depends upon the environment in which the organism lives. A trait which is adaptive in one environment may be less adaptive or even maladaptive in a different environment.

Biologists have identified several components or steps in evolution by natural selection. A listing of these steps will help you grasp Darwin’s reasoning as he formulated his theory of evolution and the origin of species.

Evolution can be understood as being the result of five basic facts of nature.

1. All species produce more young in each generation than can possibly survive.

2. These young vary slightly, one from another--individual variation or genetic variability. (Mutation, genetic accidents, is one source of this genetic variation, but the major source of genetic variability is sexual reproduction, the mixing of genes of two genetically different individuals, the parents, resulting in a unique genetic combination in the offspring).

3. Competition arises among individuals for food, for mates, for space, in the avoidance of predators, in resistance to disease, and in innumerable other factors that may affect chances of survival and

reproduction.

4. Those individuals which are better suited to their environment (those which are better adapted, most biologically "fit"), by virtue of the traits which they possess, have a competitive advantage, a survival and reproductive adavantage, over those individuals which by chance are less well adapted.

5. Those individuals with the survival and reproductive advantage, arising from their better adapted characteristics, reproduce in greater numbers, leaving larger numbers of offspring which likely possess those same favorable traits. Individuals lacking those favorable (adaptive) traits or possessing them to a lesser degree are at a survival and reproductive disadvantage and so are less likely to leave surviving offspring and less likely to perpetuate their less adaptive characteristics, which may in fact be "weeded out" from the species and thus disappear.

This selection of some traits for replication in succeeding generations and the elimination of other traits in future generations of the species is Darwin’s natural selection. Repetition of these processes, generation after generation, results in species change over time, evolution.

Natural selection is like a sieve or a filter, allowing some traits to pass through to future generations, while eliminating others by preventing them from passing through the "filter" to later generations. According to Darwin, this "filtering out" of unfavorable or maladaptive characteristics from a species and the retention and replication of favorable (adaptive) ones is a slow, steady, gradual process. Recent research, however, indicates that evolution of at least some traits such as beak shape and size in some species of bird may occur very rapidly (in a matter of a few years or less) in instances of extreme and rapid environmental change. This type of evolution involving "minor" changes in a trait within a species is known as microevolution. Macroevolution, the formation of a new species from an ancestral species, is a very long process involving thousands or even millions of years.

It should be noted that although Darwin’s theory emphasizes the role of natural selection in evolution and the origin of species, a few biological scientists, most notably Harvard paleontologist Steven J. Gould, believe that chance has played a large role in the course that evolution has followed. In fact, Gould believes that human beings could never again evolve, even under the same environmental forces which existed during our evolution into homo sapiens, modern human beings. He argues that chance factors played a crucial role, several times at critical turning points, in the direction that evolution followed as it eventually produced the human species. Gould does not deny evolution, nor natural selection, but simply proposes that chance frequently determines the course of evolution at many critical turning points in the evolution of any species.

Students often misunderstand Darwin's theory of evolution by natural selection. When asked to explain how, for example, giraffes might have evolved long necks from an originally short-necked species of giraffe-like creature, students reply that the short-necked animals stretched their necks in order to feed on leaves up in the trees. They then say that the longer necks attained from stretching get passed on to the offspring. This is called "inheritance of acquired characteristics" and is a mechanism for evolutionary change proposed in the 1800's by a fellow named Lamarck. However, this is WRONG. Inheritance of acquired characteristics like stretched necks does not occur and is NOT the mechanism for evolution. If so, if you go to the gym and get buff, then you should give birth to buff kids. This doesn't happen. Instead, Darwin's "natural selection" (explained above) is believed to be the correct mechanism for evolution of adaptive changes in species of organism, including the complex designs of their bodies and brains (in the case of animals--no brains in plants). One other common misunderstanding of Darwin's theory of evolution is that it proposes that we came from monkeys or apes. This is inaccurate. Darwin's theory does not propose this, but instead proposes that we, monkeys, and apes all descended from a common, now extinct primate ancestor. Human evolution is presumed from evidence in the fossil record to have included a number of pre-human species, including the bipedal species, Australopithecus, about 3.5 million years ago. This non-human was followed by the first humans, called homo habilis, about 2 million years ago, then homo erectus about 1.6 million years ago, then homo sapiens neanderthalensis from about 300,000 years ago until about 35,000 years ago, then finally our species, homo sapiens sapiens, arising about 100,000 to 200,000 years ago. Our species and the Neanderthals apparently overlapped and existed simultaneously until the later became extinct, perhaps because of competition from us. Our evolution was characterized by at least two trends, bipedalism (walking upright on two legs) and encephalization (increased brain size), in conjunction with a grasping hand (which originated in our primate ancestors who initially used these grasping hands to hang onto branches as they moved through the trees). Evolution of big brains is not the full story of human success. Evolution of specific brain circuitry that permitted us to develop our particular kind of intelligence, language, and effective cultural transmission of things we learn to future generations (for their use and for them to build upon) played major role in our success as a species. Now, why is evolution important to psychology?

Simply put, evolution helps explain the organization of behavior, the organization of minds, and the organization of the brains that produce behaviors and minds, in animals on earth including the human animal, and perhaps in forms of life which may exist on other planets. In fact, there is a new branch of psychology, evolutionary psychology, which is based on the hypothesis that human behavior and mental organization is in large part determined by our evolutionary history as a species. Learning and culture are simply superimposed upon evolutionary determinants of human behavior and mental structure. Human learning and culture themselves are only possible because of the particular evolutionary history of our species which has formed our particular type of brain.

Here are several other concepts related to evolution and our next topic, genetics, that you should be familiar with: 1) altruistic behavior--this refers to behavior which is self-sacrificing and which benefits others often at one's own expense. It is thought to depend upon "kin selection" (getting one's genes into the next generation by helping one's close relatives, and their genes, survive and reproduce) and upon reciprocal altruism ("you scratch my back now, and I will scratch yours later"). 2) concordance--the degree of correlation between individuals on some trait. Concordance is expected to be higher the more closely related two individuals are, the more genes they have in common, and to the degree that the trait has genetic determination. Concordance on a behavioral trait such as schizophrenia in identical twins vs. non-identical twins gives us some help in guessing how much genetics contributes to the behavioral trait. 3) ultimate causes: refers to evolutionary causes; proximate causes refers to immediate causes such as physiological factors and immediate environmental factors acting on the organism to determine behavior.

Genetics

One useful way to approach an understanding of living things is to ask where the information comes from that organizes them into the complex forms that they take. Organisms are not randomly constituted. They are highly structured in very specific ways. Hearts, lungs, livers, bones, brains and other organs are composed of cells of specific types, organized in very precise and orderly ways. Brains, especially in very complex animals, are extremely structurally complex and highly ordered arrangements of cells and specific connections between cells. And cells themselves are extraordinarily complex arrangements of matter. To accomplish all of this order, all of this structural organization, requires enormous amounts of information, an incredibly complex "blueprint" which guides development of the organism from a single fertilized egg (from which we all came) into a complex, integrated, well-functioning plant or animal.

Again, the key question is:

Where does all this information come from?

What is the origin of all of this information that orders living matter into such complex, organized forms (cells, tissues, organs, organism), which function so well, in exactly the "right" ways?

How does the "right" information get into the organism to guide its successful development? How is that information coded and stored? How is it transmitted?

If you are religious in the traditional Christian sense, you might answer that God, as Creator, supplies the information that has made living things alive. If we accept this supernatural view, then the role of the Creator is not only to create matter and energy, but also laws which govern the way matter and energy behave, such as the laws of motion, the law of gravity, and other physical laws of physics and chemistry. But, in addition, God must have also created the information that organizes matter and energy into living organisms. On this view, God the Creator, created life by creating the "right" information, information that would order matter and energy into forms which we call plants, animals, bacteria, viruses, and other forms of life on earth.

As I discussed earlier, there is nothing wrong with this view. It may be correct. A Creator may be the source of the information that organizes matter and energy into living forms.

However, science is not content with this sort of answer for one simple reason. Science attempts to find explanations for things in terms of natural laws. Science also assumes materialism, that everything in the universe is composed of matter and energy. A Creator is a supernatural being, not a part of nature, not subject to natural law, not material (not composed of matter and energy). So, although, I grant you that a religious explanation for the origin of life may be feasible, might even be correct, scientists, when playing the game of science, require that explanations for things in our universe be framed within the realm of natural law, not supernatural forces. In short, scientists attempt to explain phenomena in our universe, including living things, by discovering natural, physical laws.

Darwin, himself, the originator of the theory of evolution by natural selection, is a good example of this. Darwin was himself religious. His father and his wife were religious. There was even a minister in the family. Darwin had been taught the Christian view that God had created human beings and all other forms of life on earth, but he was not content with this view, because, as a scientist, he wanted to discover a natural law that could explain the origin of life and the origin of species. This commitment to a search for a law of nature to explain life and the myriad forms of plant and animal on earth resulted in the theory of evolution by natural selection.

The first key question posed above in this section on genetics is where does the information come from that organizes living things into the complex, well-functioning forms (plants, animals, viruses, etc.) that we see on earth. Where did the correct information come from that makes us, and other living things, so "perfect" for life on earth?

The scientific view is that this information has come from and has been "perfected" by natural selection. Generation after generation, eon after eon, of natural selection has "created", over millions of years, the correct information needed for survival and reproduction.

Natural selection accomplishes this in two ways. First, by preserving information that leads to successful adaptation. This occurs when the better adapted individuals of a species reproduce themselves and pass on to the next generation, the information (genetic information) stored within them. Secondly, by "weeding out" information that leads to less successful adaptation. This occurs when the individuals of a species that are less well adapted to the environment die before they can reproduce. The reduced reproductive success of less well adapted individuals, who tend to die before they can reproduce precisely because they are less well adapted, tends to eliminate from future generations the information (genetic information) that makes them less well adapted. The elimination of the unfit (the less well adapted individuals) and the information that has made them less well adapted, and the successful reproduction of those individuals of a species that are better adapted, and the resulting preservation of the information that has made them better adapted, shapes forms of life into better and better adaptive "designs."

It is how birds got feathers and light-weight bones, how plants developed photosynthesis, how fish have gotten such efficient fins, how desert ants "know" how to navigate across the desert floor, how lions "know" to hunt, how dogs "know" how and with whom to mate, how humans "know" to live in groups, to like fats and sweets, to make and recognize facial expressions, to create civilizations. Natural selection is the "sculptor" of life on earth. At least, this is the current scientific view, as embodied in the theory of evolution by natural selection; and it is this view that we will take in the discussions that follow.

Darwin imagined this process to be similar to what animal breeders of his time did. Darwin had observed that animal breeders could selectively breed animals for a particular trait, just by picking those animals for breeding that had the desired trait most developed. For example, to produce a breed of fierce fighting dog, Darwin knew that animal breeders could accomplish this simply by selecting the most aggressive male and female dogs each generation for breeding. Those dogs which were less nasty simply weren’t bred. After a few generations of this artificial selection, a new strain of fierce fighting dog could be produced. A kind of human directed artificial evolution could be produced. Darwin imagined that natural selection worked similarly, except that there was no animal breeder doing the selecting as to who would breed and who would not, instead the environment, nature, did the selecting by killing off the less fit individuals before they could breed and pass on their less well adapted traits. Since nature was the selective force, not an animal breeder, Darwin chose the term natural selection to describe the process by which evolution occurred.

Though Darwin described the natural law by which information within living organisms comes to be "perfected" for survival and reproduction, he did not understand (no one of his time did) how this information was stored in organisms or how precisely it was transmitted over generations. The laws of heredity were discovered by a monk named Gregor Mendel. "Genes" was the name given to the units of heredity. It was not until the middle of the 20th century that the chemical structure of genes was discovered and described, about a hundred years after Darwin.

Genes are composed of a molecule called DNA, deoxyribonucleic acid. Two scientists, Watson and Crick (the later is currently working at the Salk Institute at the University of California, San Diego doing brain research) discovered that DNA has a double helix structure. Two long strands of smaller molecules called bases twist around one another like two coiling snakes.

Genetic information, which directs the growth of the organism from a single fertilized egg, is coded by the specific sequence of bases making up the DNA molecules composing the genes of the individual.

The genetic code may be thought of as being similar to the Morse code. In Morse code, the sequence of dots and dashes stands for letters and words and so communicates meaning. In the genetic code, there are not just two coding states, dots and dashes, but four different bases which can be strung into an enormous variety of very long sequences. The DNA code is like a four-letter alphabet, with incredibly long "words" and "sentences" possible. Again, it is the sequence of these "letters", the bases, in the DNA molecule that codes and stores, in a molecular code, genetic information. It is this information that organizes all the complexity of an organism’s physical structure and function.

As discussed above, this information has been acquired by the species over its long evolutionary history via the operation of the laws of natural selection (differential rates of reproduction such that the better adapted individuals in any generation reproduce more surviving offspring, preserving and refining, over generations, the information that has led to successful adaptation to the environment).

The genetic makeup of an individual organism, that is, the genetic information that the individual carries in its genes, is called the organism’s genotype. But genes alone are not all that determines the traits that the organism finally ends up with. The genes interact with the environmental conditions the individual organism develops within, so that the actual traits one ends up with are called the phenotype, an interaction between genes and current environment. An example is the effect that nutrition has on brain development in humans. An individual may inherit a genotype that might have the potential to produce a brain of a genius, but if that genotype is forced to develop in an environment which does not supply adequate protein in the diet, then that potential genius may have impaired brain development resulting in a phenotype, an individual, who actually develops only average intellectual ability or even less than average, in spite of the much higher genetic potential contained in his or her genotype.

Chromosomes are long strings of genes. Genes and chromosomes occur in pairs in all cells of the organism except its reproductive cells (gametes), sperm in males and eggs or ova in females. In the gametes, the genes and chromosomes are half the normal number contained in other cells of the body in which the genes and chromosomes are paired.

The genes or chromosomes of a pair are called homologous genes or chromosomes. If the homologous genes (genes of a given pair) are the same, they are homozygous, if different, heterozygous or allelles. The suffix "zygous" refers to zygote, meaning a fertilized egg (the origin of us all).

Heterozygous genes can have a dominant-recessive relationship. In this case, the gene that gets expressed in the phenotype is said to be dominant. The gene that is not expressed in the phenotype is said to be recessive. An example is human eye color. There are genes that code for blue eyes and genes that code for brown eyes. In symbol form, a heterozygous genotype for eye color would be : Brbl

The capital letter for Br indicates that brown is dominant and that the Brbl genotype is likely to produce a brown-eyed phenotype. This is when there is complete dominance operating. If there is incomplete dominance, which sometimes occurs in the case of human eye color, then the genotype Brbl will produce an individual with green or hazel eyes.

The only way to get blue eyes is to have the homozygous recessive genotype: blbl.

Traits like human eye color which are determined by a single gene pair are called simple patterns of inheritance. There is a simple method for predicting genotypes from various matings for traits with simple patterns of inheritance. I call it the box method. Simply draw a square. Bisect it with a horizontal line, and then again with a vertical line. This results in 4 smaller squares. On the border of the original, larger square put the genotype of each parent, father along the top border, mother along the left vertical border.

father: bl bl

mother: Br bl

Here we have a father who is homozygous recessive (blbl) and a mother who is heterzygous (Brbl) for eye color. Once you have this set up, you can now examine the various possbile combinations of genes from father and mother which will produce the eye color of their offspring. The two genes of each pair of genes (from father, from mother) are separated because they act independently of one another because each is the gene in the gametes (reproductive cells) of each parent. In other words, this mother produces two types of egg, one type (about 50% of her eggs) contains the gene for brown eyes (Br), and the other type of egg she produces (50% again) contains the gene for blue eyes (bl). So depending upon which egg of hers is fertilized, she will contribute either a Br gene or a bl gene to the offspring. Of course, in this case, since the father’s genotype for eye color is blbl, he only produces sperm carrying the bl gene for eye color. Now it is possible to examine the various possibilities. If a bl-carrying sperm (the only kind of sperm this particular father has) fertilizes a Br-carrying egg, then the offspring will have a Brbl genotype for eye color. If a bl-carrying sperm fertilized a bl-carrying egg, then the offspring would have a blbl genotype, and thus blue eyes, blue-eyed phenotype. Work out all the possibilities and you can see that half of the children from this marriage are likely to have Brbl genotypes from eye color (brown eyes in the phenotype if we assume complete dominance) and half are likely to have blbl genotypes (and blue eyes). You can try other matings. For example, try a father that is BrBr with this mother. Will there be any blue-eyed children possible from such a mating? (Hopefully, you determined that the answer is "no").

This method can be used not only for physical traits like eye color, but also for any trait, including behavioral or mental, which is determined by a single gene pair (remember this is called a simple pattern of inheritance). One example of a mental trait determined by a single pair of genes is mental retardation caused by the disease PKU, phenylketonuria. It is the result of two abnormal recessive genes, that is, it is a homozygous recessive trait. One PKU gene from each parent is necessary to get the disease. One normal gene and one PKU gene results in a carrier, someone who doesn’t have the disease, but which carries one gene for it. Two carriers, or one carrier and a PKU diseased person, can produce a PKU offspring. One carrier, or one PKU person, and one normal parent cannot. Use the box method to verify these conclusions.

Other traits are determined not by a single pair of genes, but by many pairs of genes. This is known as polygenic inheritance and such traits are called polygenic traits. Some examples of polygenic traits are seed color in wheat, hair color in humans, human height, human weight, some personality traits, some forms of mental illness, and human intelligence. Such traits are continuous (they have a large number of values within the population in contrast to discrete traits such as eye color) and they are "normally distributed" in the population (if you graph the frequency with which different values of the trait, say height in human males, occurs in the population, the resulting graph is a symmetrical bell shaped curve known as a normal curve; see the textbook chapter on statistics). It is also possible to selectively breed (artificial selection) for extreme values of a trait that is polygenic. For example, I reported at the 1974 convention of the Western Psychological Association results of an experiment in which I selectively bred for taste aversion learning in rats (their ability to learn what foods make them sick). This is done by breeding the better learners with other better learners, and the poorer learners with other poor learners. In just five generations of selective breeding, two groups resulted, very good learners and very poor learners with no overlap in learning ability between the two selectively bred groups. This not only demonstrated that this learning ability has some potent genetic determinants but also showed that the ability is polygenic. Other psychologists have obtained similar results for other behavioral/mental traits including maze learning in rats. Also demonstrated is individual differences among the rats in a behavioral trait, learning ability, at the outset of the experiment. Individual differences in traits of all sorts, anatomical, physiological, and behavioral/mental, are essential for evolution to occur. Individual differences provide the range of genetic alternatives from which natural selection can then "pick" for reproduction or eliminate by early death. Because genetic variability is so essential to evolution, there are mechanisms to assure that there is plenty of variability within any species. As mentioned above, sexual reproduction, the mixing of genotypes of the two parents to form a new unique genetic combination, is the major source of genetic variability within any species. This source of variation within a species is enhanced even more by the fact that during gamete formation (egg and sperm production) processes called independent assortment and crossing over produce genetic variation even among the eggs of a female or the sperm cells of a male. That’s why siblings are not identical to one another in their genetically determined traits even though they come from the same parents. Sexual reproduction creates an enormous amount of genetic variability within a species Every trait in every species shows genetic variation.

A good example of genetic variability is human faces--no two are identical, except identical twins, and yet the variation occurs within limits--there are no horse faces, alligator faces, bird faces, or gorilla faces among humans, but only human faces, and yet within these constraints no two human faces are exactly the same. This is also true of human brains, or livers, or digestive systems, or any other trait. There is always genetic variability, within species constraints, in every trait of every species. Without this variability, the raw material upon which natural selection operates, the process of evolution would not have been possible.

These facts help us understand why sex exists.

Sexual reproduction is very costly biologically. Male and female have to get together. This involves a substantial expenditure of energy (in calories) and time. There are complex behaviors involved such as courtship (in animals as well as in humans), competition from others for one’s mate, which can include threats and perhaps fighting and even potential death from competitors or one’s own jealous mate. There is the risk of sexually transmitted disease.

It would seem much more efficient and less dangerous if nature had arranged things so that we could simply mate with ourselves (asexual reproduction), a capacity that a few primitive species actually do have.

Why is it then, that most species have come to engage in the more complex and biologically costly form of reproduction, sexual reproduction? The answer seems to be that the energy and time expenditure and other biological costs of sexual reproduction are outweighed by the benefits of sexual reproduction as a source of genetic variability for the species (in contrast to asexual reproduction which does not involve the mixing of the genes of two different individuals and which therefore does not produce as much genetic variation within a species).

The mapping of the human genome (entire genetic makeup of a human being), recently accomplished by researchers, will lead to new insights into the genetic basis of many human characteristics. There are likely to be many surprises. Perhaps more of our human nature will be shown to be determined by our genetics than we have previously thought. The genetic information that organizes many human behavioral and mental traits is likely to be identified in the next several years. This will have a profound impact on the field of psychology and upon how we view ourselves. If it turns out that many of our behaviors, mental traits, and even personality traits are genetically influenced, then how will this affect our concept of human free will?

BRAIN AND NERVOUS SYSTEM ANATOMY AND FUNCTIONS

For some excellent photos of the human brain go to the following website: http://www.vh.org/Providers/Textbooks/BrainAnatomy/BrainAnatomy.html ALSO GO TO THIS WEBSITE FOR GREAT OVERVIEW OF NERVOUS SYSTEM, NEURONS, AND BRAIN: http://faculty.washington.edu/chudler/introb.html Remember, as discussed earlier in this lecture, the 17th century French philosopher, Rene Descartes, believed that the mind is not dependent upon physical events in the brain, but that mind and the body (and brain) function independently. Also recall that most scientists reject this mind-body dualism and instead believe that the mind and behavior are dependent upon the brain and physical events within it.

This is actually quite a striking position when examined closely. It implies that every mental event (every thought, every feeling, every sensation, every memory, even every belief) is really a physical event in a completely physical brain. How can matter (brain matter) make mind?

This is probably the most challenging question confronting modern science. The growing fields of neuroscience, cognitive neuroscience, and physiological psychology are producing insights from brain research which may help us one day better understand how mind out of matter might be possible.

Here, we will now examine some of the basic facts about the organization of the brain and nervous system.

As you might guess, nervous systems like bodies vary from animal species to animal species. Insects (roaches, ants, bees, etc.) and other invertebrates (such as seaslugs, lobsters, crabs, and the octupus) have nervous systems that are in many respects very different from the nervous systems of vertebrates (back-boned animals).

All vertebrate species have a similar nervous system organization--a spinal cord with nerves coming off of it going to and from the body and an enlargement at the head end of the cord, which is fairly modest in fish and amphibians, but which shows much greater size and complexity in birds and especially mammals. This increasingly complex structure, the brain, is itself composed of many different parts, some of which are found only in the more advanced and complex species.

The vertebrate nervous system is subdivided into two major divisions: the central nervous system comprised of the brain and spinal cord, and the peripheral nervous system composed of all the nerves in the body outside of the brain and spinal cord.

The Peripheral Nervous System

These peripheral nerves include the cranial nerves (which come out of the lower part of the brainstem just above the top of the spinal cord as the cord enters the skull) and the spinal nerves (which emerge from along the length of the spinal cord; there are 31 pairs of spinal nerves and 12 pairs of cranial nerves in humans).

These peripheral nerves may be input nerves, carrying messages into the spinal cord and then up to the brain, also known as sensory nerves or afferent nerves. Nerves carrying pain messages or touch messages to the spinal cord and from there up to the brain are two examples of sensory or afferent peripheral nerves. Other peripheral nerves are output nerves, carrying messages out from the spinal cord to muscles and glands, also known as motor nerves or efferent nerves. An example would be a nerve that carries a neural message out from the spinal cord to a muscle group that causes a movement of a part of the body.

In addition, the peripheral nervous system is itself subdivided into two divisions: the somatic nerves and the autonomic nerves.

The somatic peripheral sensory nerves carry neural messages from the skin into the spinal cord and then up to the brain (pain, touch, temperature sensations result). The somatic motor (peripheral) nerves carry neural impulses from the spinal cord to the skeletal muscles and result in movement of some part of the skeleton and thus of some part of the body.

The autonomic nerves serve the internal body organs such as heart, lungs, stomach, blood vessels, sweat glands, adrenal glands, etc. Sensory autonomic nerves carry neural messages from internal body organs to the spinal cord and up to the brain and result in sensations such as stomach aches, "butterflies in the stomach", heart pain during a heart attack, etc. Motor autonomic peripheral nerves carry neural impulses from spinal cord to internal body organs. These motor autonomic nerves are of two types: sympathetic and parasympathetic.

The sympathetic nerves are sometimes called the "fight or flight" nervous system because these nerves become active during a perceived threat or emergency and mobilize the body’s resources to deal with it. Increased heart rate, blood pressure, breathing rate, sweat gland output, dilation of the pupils of the eyes, redistribution of blood to the brain (for faster more efficient thinking and perception) and skeletal muscles (for faster, stronger movements), stimulation of the adrenal glands to release adrenalin, decreased digestion, decreased sensitivity to pain, all occur. The body can now run faster, punch harder, jump higher, scream louder, or whatever else may help deal with the threat or emergency. Threats need not be physical to induce activity of the sympathetic nervous system. Psychological threats or stressors may be just as effective in inducing a sympathetic response.

The parasympathetic nerves have exactly the opposite effects. When active, it conserves the body’s resources. It decreases heart rate, blood pressure, breathing rate, sweat gland output; pupils constrict, adrenalin from the adrenal gland is reduced, digestion increases, as does pain sensitivity. This part of the peripheral autonomic motor nervous system is active under ordinary conditions, when the animal or human is not under any threat, emergency, or any particular stress.

In summary:

Vertebrate Nervous System consists of:

central nervous system and peripheral nervous system. Central Nervous System (CNS) consists of brain and spinal cord. Peripheral Nervous System (PNS) consists of Somatic nerves and autonomic nerves. Both of these consist of sensory (input) and motor (output) nerves. The motor autonomic nerves are either sympathetic ("fight or flight") or parasympathetic (conserve body's resources).

After having examined the peripheral nervous system, let’s now take a look at the central nervous system.

Central Nervous System: Spinal Cord

The spinal cord hasn’t changed much in the evolution of vertebrates. Aside from size differences, there’s not much difference between the spinal cord of a rat and the spinal cord of a human.

The central core of the spinal cord, known as the central gray, or the spinal gray, contains cell bodies of motor nerve cells and circuits for spinal reflexes (simple automatic, inborn responses to a specific stimulus; for example, the knee-jerk reflex, the scratch reflex, or the withdrawal reflex in response to pain like touching a hot stove). The nerve fibers (called spinal motor axons) that carry nerve messages, from the motor neuron cell bodies in the central gray of the spinal cord out to the muscles, are the nerves that compose the somatic motor peripheral nerves. Those motor neuron cell bodies receive their input from nerve pathways for movement which originate in the brain. One neurological disease that selectively kills these somatic motor nerve cells while leaving the brain and other peripheral nerves (sensory nerves and autonomic motor nerves) unaffected is called ALS (amyotropic lateral sclerosis) or Lou Gehrig’s disease, after the famous baseball player who died from it.

Surrounding the central gray core of the spinal cord, there is another part of the spinal cord which is white and so is called the spinal white matter. The spinal white matter is essentially a bundle of cables, or cable-like neural tracts, which connect brain and body. Of course, severing the cable, the spinal white matter, can isolate the body from the brain resulting in paralysis and loss of sensation in parts of the body below the level of the cut in the spinal cord. Christopher Reeve is paralyzed and has little sensation from the neck down because of an accident which severed his spinal cord at the neck. Nevertheless, he will still have reflex movements such as the withdrawal reflex because the circuits for this and for other spinal reflexes are within the spinal cord. Curiously though, he will have no conscious sensations from any stimulus such as a match to the foot that will induce the withdrawal reflex. Notice that voluntary movement requires connections via the spinal white matter from the brain, but reflex movements do not.

Central Nervous System: Brain

The brain of vertebrates is subdivided into hindbrain, midbrain, and forebrain. Hindbrain and midbrain together are called the brainstem. Refer to pictures and diagrams of the brain and nervous system in your textbook as you read this lecture. Try to find the structures as you read about them.

The Hindbrain consists of three brain structures: the medulla, the pons, and the cerebellum.

The Medulla is the upward extension of the spinal cord into the skull. As such, part of it is just the upward extension of the spinal white matter into the skull. In addition, there are clumps of nerve cells (the general name for such clumps is nuclei when found in the central nervous system and ganglia when found in the peripheral nervous system) lying among the white matter of the medulla. These nuclei in the medulla control basic life support functions - - heart rate, breathing and blood pressure. As a consequence, damage here is usually fatal.

The Pons, also part of the hindbrain, lies just forward of the medulla on the ventral or belly side (front in us) of the brainstem. It contains nuclei that also regulate breathing and others which are involved in REM sleep, another name for Dream Sleep. There are two bsic types of sleep (consisting of several stages) - - Non-dream sleep and dream (REM) sleep. Each type of sleep has distinct characteristics. One of the main differences is in the brain waves (EEG, electroencephalogram) that are produced by the brain in each type. In non-dream sleep, the EEG shows large amplitude ("high" voltage), low frequency waves called Delta waves or slow waves (about 0.5 --2 cycles or waves per second, cps). By contrast, Dream sleep (REM sleep) shows high frequency (18 - 30 cps) waves in the EEG called Beta waves -- the same type of EEG wave that occurs during alert, attentive, wakefulness. In addition, during dream sleep, as the name implies, subjects when wakened usually report they had been drreaming. During the Non-dream or Delta sleep (also called Slow Wave Sleep), subjects rarely report they had been dreaming. In addition during dream sleep, REMs (rapid eye movements) occur under the closed lids of the sleeper.There are other changes that occur during REM sleep as well. In summary, during REM or dream sleep the following occur:

1. subjective dreams

2. REMs

3. beta waves in the EEG (like during attentive wakefulness)

4. muscle twitches in the extremities

5. complete relaxation of the neck and trunk muscles

6. increased heart rate, breathing, and blood pressure

7. very high brain metabolism (the brain burns a lot of energy at a rapid rate, indicating it is very active during dream sleep)

8. reflexive signs of sexual arousal (erections in males and vaginal lubrication in females) unrelated to dream content (you could be dreaming about sailing, a barbeque, or your taxes and still you’d show the characteristic signs of sexual arousal. Freud, the founder of psychoanalysis, mistook such physical signs during sleep in infants as evidence of infant sexuality, one cornerstone of his theory).

Now, back to the Pons. The Pons contains nuclei which are part of the brain circuit that triggers periods of REM sleep (each about 20 minutes long), approximately every 90 minutes throughout the night. Human adults spend about 20% of their sleep time in REM sleep; human infants spend about 80% of their sleep time in REM sleep. This much larger percentage of sleep time spent in REM during infancy, a period of rapid brain growth, has led to speculation that REM sleep may be a time during which the brain is growing and repairing itself, or growing new connections between cells to store new memories. The very high rates of brain metabolism (high rates of glucose and oxygen utilization) during REM sleep is consistent with this hypothesis.

The Cerebellum is located on the dorsal (back, like a dorsal fin) side of the brainstem. It sits atop it, almost appearing as a little brain unto itself (remember to refer to pictures of the brain in your textbook to locate the structures we discuss). The cerebellum is involved in several ways in the control of movement -- muscular coordination, body balance, and the formation and storage of "motor programs" for learned skilled movements such as dancing, playing piano, doing a gymnastics routine, and even tying your shoes or eating with chopsticks. Damage to the cerebellum does not cause paralysis because other brain areas are also involved, but such damage does make movement difficult, uncoordinated, and stiff and jerky. In mammals, like us, another area called motor cortex (see below) initiates movement commands, rather general in nature, and the role of the cerebellum is to compute and control the details of the movement to make it smooth and fluid.

Recent research indicates that the cerebellum may also be involved in computing the timing of movements to coordinate them, and it may also be involved in some aspects of the perception of time such as judging durations of intervals of time (Richard Irvy at Cal Berkeley has hypothesized that there may be cells in the cerebellum sensitive to specific temporal durations). Richard Thompson at the University of Southern California in Los Angeles has shown that the cerebellum is the site of simple forms of motor learning (classical conditioning of the eyeblink response in rabbits, specifically, and probably classical conditioning of some other motor responses; see lecture on Learning for more about classical conditioning).

Forward of these hindbrain structures is the Midbrain. On the dorsal (back) side of the midbrain are four bumps, the inferior and superior colliculli. The former are relays in the auditory system (hearing) and the latter control reflex movements of the eyes.

The midbrain structure of most interest to us is the Ascending Reticular Activating System (ARAS), sometimes known simply as the Reticular Formation. It lies in the core of the brainstem, running from the core of the upper spinal cord to the top of the core of the brainstem near a structure called the thalamus (itself part of the forebrain).

The name of this structure reveals much about its functions. It is an "activating" system which activates the upper regions of the brain, the forebrain, thereby regulating the states of consciousness or alertness of the animal or human to which it belongs. The ARAS plays a major role in the sleep-wakefulness cycle of animals and humans. When it is active and sending "ascending" impulses up to the cortex (see below) and other forebrain structures, the forebrain and the animal are awake, alert, and processing information from the environment at high rates. When the ARAS is less active the animal may be less alert, or even drowsy. When the ARAS is very inactive, the animal will drift into non-dream or Slow Wave sleep. There appears to be some sort of internal "clock" that sets us and other animals on a 24-hour sleep-wake cycle. Damage to the ARAS, such as in an auto accident, can cause coma; so can swelling of the brain which compresses the ARAS causing a temporary coma until the swelling subsides.

Forward of the midbrain (on top in an upright animal like us) is the forebrain. The forebrain is a more recent development in the evolution of the brains of vertebrates. Structures here are more complex and are involved in the more complex behavioral and mental functions of animals and humans.

We will start of our tour of the forebrain from the bottom and work our way up.

At the base of the forebrain, just above the very back of your throat, but inside your skull, is the Hypothalamus. It is about the size of a quarter in a human being, yet it includes over 30 different nuclei involved in various functions. In short, the hypothalamus is involved in control of basic biological drives (hunger, thirst, and sex), in emotion, in the regulation of body temperature, and in the stimulation of the autonomic nervous system, especially the sympathetic branch (remember "fight or flight").

There is also an import "pleasure circuit" that runs through the hypothalamus. It might surprise you that the brain has pleasure circuits, but your ability to experience pleasure is dependent upon such circuits. Their function is to make you do what is good for you and for the species. It is no accident that things which are beneficial (good food, good friends, good sex, etc.) activate pleasure circuits causing you to repeat behaviors that lead to these things. Damage in the hypothalamus can cause abnormalities in any of these functions, in humans, as well as in other animals. Electrical stimulation of the hypothalamus through implanted wires (electrodes) can activate emotions, pleasure, fear, attack, sexual motivation, feeding, drinking, and cause changes in body temperature. A woman patient in Japan after having electrodes implanted in this region of the brain for medical reasons began flirting, and then proposed marriage to a doctor who was interviewing her, when electrical stimulation was delivered to this part of her brain.

In addition, the hypothalamus also regulates the Pituitary gland, which is located just beneath it (and therefore, also, just above the very back of your throat inside your skull). The pituitary gland is known as the master gland because it regulates all the other endocrine glands, which release hormones into the bloodstream. In essence, the hypothalamus acts as an interface between nervous system and hormonal system. An example of the interaction of hypothalamus, pituitary gland, and an endocrine gland is the regulation of the reproductive cycles, ovulation and menstruation, in women. These cycles are actually controlled by the hypothalamus which releases hormones called hypothalamic releasing factors onto the pituitary. This stimulates the pituitary to release hormones which stimulate the ovaries to release an egg (ovulation) and to release estrogen and progesterone hormones which act on the uterine lining causing it to thicken in preparation for implantation of a fertilized egg. If pregnancy doesn't occur, the uterine lining is shed (menstruation). Stress and emotion (also controlled in the hypothalamus) can interfere with these hypothalamic processes causing a woman to be late or to completely miss a menstrual period.

Just above the hypothalamus and pituitary is the Thalamus (located just about in the center of your brain). The thalamus is a collection of several nuclei which act roughly as "sensory relays" for all the senses except the sense of smell (olfaction). Each of these senses has its own nucleus within the thalamus. For example, for vision the thalamic relay nucleus is called the Lateral Geniculate

Nucleus (LGN), for hearing (audition) it is the Medial Geniculate Nucleus (MGN).

These are called relay nuclei because they are located in the sensory pathways between the sensory organ (the eye, for example) and the corresponding sensory area of the cerebral cortex (visual cortex, for example), where higher order information processing and probably conscious sensations actually occur (in this case, visual sensations of luminosity, color, etc.). However, these sensory nuclei of the thalamus are not just passive "relays" but these nuclei perform complex information processing themselves before the information in the form of neural code (patterns of nerve cell impulses) is transmitted on to the cortex. We will discuss the LGN further when we come to the material on the visual system in the Sensation and Perception lecture.

More widely distributed in the forebrain are several structures collectively known as the Limbic System. These structures interconnect with one another and with the hypothalamus and are all involved in emotion in one way or another. The limbic system has been called the "emotional brain." The limbic system is composed of the hippocampus, amygdala, cingulate gyrus, and a few other structures we will not deal with here.

The hippocampus has a special involvement in memory, as well as in emotion. To understand its role, you must know something about memory.

Memory appears to have at least three stages - - sensory memory, short-term memory (temporary, lasting seconds to a few minutes), and long-term memory (more or less permanent). Close your eyes for a moment and you will have a brief image in your mind of what it was you were just looking at - - that's visual sensory memory, very brief but very detailed. Short-term memory (STM) lasts a very short time and then is lost or is converted into long-term memory (LTM). The process of conversion of STM into LTM is called "memory consolidation." The hippocampus is essential for consolidation of STM into new LTM. This was discovered by accident in the 1950's when a patient known in the medical literature by his initials, H.M., had both hippocampi removed by a neurosurgeon to control his severe epileptic seizures originating from his hippocampi. All seemed fine after the surgery until it was noticed that H.M. couldn't remember new events after his surgery for more than a few minutes. To this day, he still thinks Eisenhower is president of the U.S. He knows nothing about the Space Shuttle, home computers, the collapse of the Soviet Union, or anything else that has happened since the day of his surgery in 1956. He and his wife moved to a new house. He still frequently ends up going "home" to the old house, having no permanent knowledge of the move to the new house. He reads the same page in a book over and over because he forgets what was at the top of the page by the time he gets to the bottom of the page. Close relatives have died since his surgery in the 50's, but he can't remember that and so repeatedly wonders why he hasn't seen Uncle Fred or brother Ted in a while. When told they have died, he mourns, but forgets why he is crying in a few minutes. When he is told again later about their deaths he mourns all over again, as if he is hearing the news for the first time, but again in minutes he forgets why he's sad. The loss of both of his hippocampi has caused H.M. to lose the ability to consolidate any new long-term memories of events or facts (memory for events and facts is called Declarative memory). However, surprisingly, H.M. has normal ability to learn and remember (even for long periods just as long as a normal person) new skills that he learns (this is called Procedural or Motor Memory). That H.M. and other hippocampus-damaged patients lose ability to consolidate declarative memories but not procedural or motor memories indicates that the two types of memory depend upon different brain circuits. Though the hippocampus is necessary for consolidation of new long-term memories, it is not where long-term memories are stored. H.M. did not lose any of his old long-term memories (those formed before his hippocampalectomy), only the ability to consolidate new long-term declarative memories.

The amygdala, like the hippocampus, is located beneath the cerebral cortex of the temporal lobe (near your temple above your ear). This part of the limbic system is involved in control of aggression and attack behavior. It also seems to be involved in fear and anxiety, and perhaps in an animal's (including humans) ability to understand negative or aversive properties of stimuli in the environment. Electrical stimulation of the amygdala through implanted electrodes causes intensely violent, relentless attack behavior. In a rare form of epilepsy of the temporal lobe seizures can spread down to the underlying amygdala and cause rage and attack behavior in these human patients. Destruction of the amygdala in both animals and humans has been shown to produce a complete absence of any aggression, even in situations which would normally produce such behavior in normal individuals. For example, wild bobcats with both amygdala removed become completely tame and placid, even when provoked. There is also evidence of similar effects in humans. The anti-anxiety drugs (such as the benzodiazepines including Valium, Librium, and Xanex) apparently work to reduce anxiety by reducing nerve cell activity in the amygdala.

The Cingulate gyrus (a gyrus is a "hill" on the folded surface of the cerebral cortex) is a strip of cortex located on the inner or medial surface of the cerebral cortex just above the corpus callosum (to be discussed below). Like other parts of the limbic system, the cingulate is involved in emotion. It seems to have an involvement in the emotional response to painful stimuli. But perhaps more importantly, recent evidence suggests that it plays a role in emotional depression. In severly depressed people, there are abnormalities in the cingulate gyrus.

Next in the forebrain are the Basal Ganglia. These structures are located near the thalamus, near the center of the brain. The basal ganglia are involved in the control of movement. Along with the cerebellum, the basal ganglia help the motor cortex (see below) organize movements. Damage to the basal ganglia produces various movement disorders. The best known of these is Parkinson's Disease, recently diagnosed in the actor, Michael J. Fox, and the disease that afflicts the famous ex-boxer, Muhamed Ali. Destruction of one of the basal ganglia structures, the substantia nigra, causes a loss of a brain chemical (a neurotransmitter, see discussion a few pages below) called Dopamine. Without adequate levels of dopamine in these structures, the nerve cells there can't communicate properly resulting in the symptoms of the disease, muscular rigidity, tremors of the hands, difficulty in getting voluntary movements started, and movement difficulties in general. The treatment for Parkinson's Disease is a drug called L-DOPA, which helps replenish the levels of dopamine neurotransmitter in the brain. For many patients, the treatment is very effective in reversing the symptoms.

Next in the forebrain is the Corpus Callosum - - a broad band or sheet of neural fibers, running horizontally near the center of the brain, interconnecting the two halves of the brain. The two halves of the brain share information and coordinate their activities through the corpus callosum. If it is cut, which is done sometimes to control very severe cases of epilepsy, dramatic effects occur. In short, "split-brain" research (Michael Gazzaniga at Cal Tech in Pasadena, California) has shown that two separate minds or consciousnesses can exist in the same head (same person) when the callosum is cut. See your textbook for more details of these astounding experiments. Of interest is the fact that there are substantial anatomical differences in the size of the corpus callosum in men and women. This structure is significantly thicker in women than in men. What effects are produced by this difference in brain structure, between men and women, is unknown.

One important result from split-brain research in humans is the finding that the two halves of the brain are specialized for different mental and behavioral functions. The left hemisphere (referred to as the dominant hemisphere) is superior at language, logic, and linear kinds of thinking, but is extremely poor at tasks that require visual-spatial abilities (such as reading a map, drawing complex patterns, or imagining spatial relationships between objects). The right hemisphere (the non-dominant hemisphere) is superior at visual-spatial tasks, at holistic thinking, at artistic and creative pursuits. However, the right hemisphere has only very limited language ability.

In mammals, especially in us, these hemispheres are composed to a large degree of cerebral cortex. Vertebrates "below" the mammals (birds, reptiles, amphibians, fish) do not have cerebral cortex. See pictures and diagrams of the brain in your textbook to locate the cerebral cortex (sometimes called the cerebrum -- note this is not cerebellum, a very different structure). The cerebral cortex or neocortex is a more recent development in the evolution of the forebrain. It is involved in many complex mental and behavioral functions.

The cerebral cortex can be subdivided according to functional types - - motor cortex (involved in control of movement), sensory cortex (involved in processing information from the senses), and "association" cortex (involved in functions that are neither simply sensory or motor, but more abstract and complex). These areas of cortex can be identified by electrical stimulation of cortex during brain surgery in conscious human patients. Because the brain has no pain receptors, local anesthetics such as Novacaine (used by dentists) can deaden the scalp and the skull, making it possible to keep a patient awake during brain surgery. Stimulation of the motor cortex causes movements of parts of the body. Stimulation of sensory cortex causes various sensations to be reported by the patient (for example, one patient, during stimulation of his somatosensory cortex -- for skin sensations, said in amazement, "I feel something on my teeth." When the electrode was moved slightly to a nearby point on the cortex, he said, "Now, it's on my tongue. Something's on my tongue." Stimulation of the visual cortex produces visual sensations in the patient such as flashes of luminosity or color, even in a dark room. Electrical stimulation of the auditory cortex produces noises in the mind of the patient and tastes when taste cortex is stimulated or smells when smell cortex is stimulated with a surface electrode applied by the neurosurgeon. Aside from telling us what different parts of the cortex do, these findings are philosophically interesting because these results suggest that conscious sensory experiences, so called "sensory qualia", are in the brain. This means that properties like smells, tastes, color, brightness, and so on are not properties of the external world (as we generally assume) but instead are properties of the mind, and exist only there, when certain cells in the brain are activated.

More commonly, the cerebral cortex is subdivided into anatomical regions called lobes. There are four of these -- the frontal, parietal, temporal, and occipital lobes. Be sure to refer to pictures and diagrams of the cerebral cortex in your textbook.

In humans and most mammals, the cerebral cortex is folded so that its surface has "hills" (gyri, plural of gyrus) and "valleys" (sulci, plural of sulcus, or fissures). Major fissures on the surface of the cortex are used as landmarks demarcating boundaries between lobes. For example, the frontal lobe extends from the front of the cortex (just behind your forehead) to the central fissure, located about midway along the length of the cerebral cortex. Behind the frontal lobe is the parietal lobe. Below the parietal lobe and the posterior part of the frontal lobe is the temporal lobe. Behind these, at the very back of the brain, is the occipital lobe.

The front part (anterior) of the Frontal Lobe in humans, the prefrontal cortex, is involved in emotions, the ability to plan ahead, to anticipate consequences of one's actions, and in social inhibitions (your ability to inhibit your impulses when their expression is socially unacceptable). Damage here can cause a previously normal person to become combative, emotionally volatile, and sexually uninhibited and may even cause one to lose their "conscience." It has been suggested that at least some psychopaths (people who commit murder and other mayham without regret) may have frontal lobe damage. (Do you think that a brain abnormality such as this should make a person not legally responsible for their criminal actions?) In the posterior (toward the rear) part of the frontal lobe, there is a gyrus, the precentral gyrus, just anterior to the central fissure. This is primary motor cortex, involved in production of voluntary movements. It is organized by body area, and, in fact, there is a mapping of the body onto the surface of the primary motor cortex, but the mapping is inverted. Adjacent areas of primary motor cortex serve adjacent body areas, but the upper body and head are controlled by the lower parts of the precentral gyrus and lower parts of the body by upper parts of the precentral gyrus.. Electrical stimulation in primary motor cortex (located in the precentral gyrus of the posterior frontal lobe) causes movements of specific body parts in conscious human patients during brain surgery. However, the patients observing the behavior occurring in their own bodies feel as if something else had moved them.. One patient said, when subjected to this brain stimulation "Something moved my arrm." Interestingly, the role of the prefrontal cortex in movement was discovered by two Austrian research physicians, Fritz and Hitzig, experimenting with electrical stimulation of the brains of dogs, and then later, after they had joined the medical corps of the Prussian Army, upon humans with head wounds, they found on the battlefields of Europe. Also in the LEFT frontal lobe of humans, just forward of the head control region near the bottom of the primary motor cortex, is Broca's Area, for language expression (the ability to speak and write). This is named after the famous pioneering neuroanatomist, Paul Broca, who speculated, after observing a common area of damage in the cortex of several patients who had lost language abilities, that the damaged area must be critical for language. For about 10% of the human population, Broca's area is found in the right frontal lobe, instead of the left. This is more common in left handers, but still most left handers, and even more of right handers, have language functions localized mainly to the left frontal lobe. Damage to Broca's area causes Broca's aphasia (aphasia means language disorder due to brain damage), characterized by difficulties with speech, writing, or both, depending upon the specific location and extent of the damage within Broca's area.

Right behind the precentral gyrus is the central fissure (dividing frontal lobe from the more posterior parietal lobe), and just behind the central fissure is the postcentral gyrus (in the Parietal lobe). The postcentral gyrus is the primary somatosensory cortex, where inputs from the skin are processed to produce conscious skin sensations such as feeling of heat, touch, or pain. Again, as was the case with primary motor cortex, the body surface is mapped out in an orderly way onto the surface of the cortex. Again, this mapping is inverted. The more sensitive body parts have the largest areas of primary somatosensory cortex devoted to them (lips, tongue, genitals, and fingertips). Behind (posterior) to the postcentral gyrus is parietal association cortex, involved in some very complex and abstract sensory processing related to comprehension of spatial relationships among things in the environment, especially such relationships among one's body areas. Damage in the RIGHT parietal association cortex is especially potent in producing a syndrome called "unilateral neglect." In this syndrome, the patient no longer understands that the left side of their body belongs to them. Even standing in front of a full length mirror, they still don't understand.that the left half of their body belongs to them. They dress only the right side of their body, groom only the right side, brush their teeth only on the right side, etc. They deny injuries that might occur to the left side of their body. They completely ignore the left side of their body, even to the point that they complain to their doctors that something is following them, even to bed and even to the bathroom, and they say that they are getting very tired of it. The thing they are complaining about that's "following them" is the left half of their own body.

The Temporal lobe, just below the parietal lobe, near your ear, contains primary auditory cortex which processes complex sound patterns and sequences. Electrical stimulation here causes patients to "hear" various unidentifiable noises. The left temporal lobe also contains Wernicke's Area, for language comprehension. Damage here produces Wernicke's aphasia, involving difficulties in comprehending speech and/ or writing, which leads to the production of nonsensical speech (the patient believes they are speaking meaningful sentences, but in reality, they frequently produce gibberish without knowing they are doing so. Since they have trouble understanding speech, including their own speech, the patient cannot successfully monitor the words they are producing. This lack of feedback causes words to come out which the patient doesn't intend and yet the patient continues to mistakenly believe they are saying what they intended to say). Buried beneath the temporal lobe cortex is the amygdala and hippocampus, both part of the limbic system involved in emotion, and in the case of the hippocampus, also memory. Thus, damage to temporal lobe or electrical stimulation of it, can affect emotions and memory. In the 1950's, a neurosurgeon named Wilder Penfield found that electrical stimulation of the temporal lobe of conscious patients during brain surgery caused them to report that they were experiencing vivid memories. Interestingly, the pioneering neurologist, Hughlings Jackson, reported that people with what has been termed the temporal lobe syndrome, due to abnormal seizure activity from the region, show an "inordinate preoccupation with philosophical and religious abstractions." A former UC San Diego neurologist, Arnold Mandell, hypothesizes that seizure-like "kindling" in the hippocampus produces religious ecstacies and Mandell in one research article asks, "is God in the brain."

The Occipital lobe is the visual cortex. Electrical stimulation here in conscious human patients causes them to "see" luminous and colored flashes in their visual fields, even in a completely dark room. This demonstrates that the luminosity and color that we "see" in the external world, and which we ascribe to it, are really not in the world nor properties of light, but in our heads. This suggests that bats which use sound waves to navigate through dark caves may "see" objects as clearly as we do; they may get visual-like experiences of their world based upon sound waves rather than light waves. The dark cave may be experienced by them as brightly lit, not by light, but by sound waves used by their brains to make mental images of their world. More about these ideas in my lecture on Sensory Systems and Perception.

The central area of the occipital lobe is called primary visual cortex. The surface of the retina, the light sensitive surface at the back of the eyeball's interior, is mapped out on the surface of the primary visual cortex. This orderly mapping is important in the coding, by the cortex, of the size, shape, and locations of objects in visual space. Damage in the occipital lobe causes blindness, called "cortical blindness," affecting only a part of the visual field or all of it, depending upon the location and extent of the damage to the primary visual cortex. Surrounding the primary visual cortex, the rest of the occipital lobe contains secondary and third level visual cortex. These are involved in more complex visual processing tasks. In the parietal lobes and the temporal lobes, there are additional visual areas, involved in very high-order visual processing such as color perception, spatial perception, visual memory, and visual recognition of objects. See your textbook and my lecture on Sensory Systems and Perception for more about these topics. The production of visual qualia, such as sensations of color and luminosity, and other aspects of visual perception are discussed in more detail there.

In summary:

BRAIN consists of Hindbrain, Midbrain and Forebrain structures.

Hindbrain contains:

Medulla, pons, cerebellum

Midbrain contains:

Ascending Reticular Activating System (ARAS), the superior and inferior colliculli

Forebrain contains:

Hypothalamus, pituitary gland, thalamus, basal ganglia, limbic system (hippocampus, amygdala, cingulate cortex), corpus callosum, cerebral cortex (frontal lobe, parietal lobe, temporal lobe, occipital lobe)

Of course, the brain is an organ of the body. As such, it is composed of cells, nerve cells, known as neurons, and supportive cells, called glial cells or glia. There are enormous numbers of cells composing the brain. The human brain is estimated to have somewhere between 50 billion and 100 billion neurons and at least that many glia. These neurons interconnect with one another in astoundingly complex circuits. One neuroscientist has estimated that the number of potential interconnections between the neurons in a single human brain exceeds the number of atoms in all the stars in the entire universe, making the brain, by far, the most complexly organized piece of matter known to exist.

What are these neurons like? How do they work? How do they communicate with one another? How might complex circuits formed by their interconnections with one another produce our perceptions, thoughts, memories, learning and emotions - - in short, our minds?

NEURONS

Neurons have three major structural parts - - the soma or cell body, the axon, and dendrites. See the drawings of neurons in your textbook. The entire neuron is bounded by a membrane, the neural membrane.

The soma or cell body contains organelles, common to all types of cells in the body, involved in the basic metabolism of the cell. The soma also contains the nucleus, where the genes and chromosomes (and the DNA within them) are located.

Neurons communicate with one another, across gaps between them known as "synapses", by the release of chemicals (neurotransmitters or simply transmitters) from one nerve cell onto the next neuron. The neurotransmitters involved in this communication between neurons are manufactured in the soma of the neuron and are then transported down a long axon where they are stored until release.

Coming out of the soma, like a hose, is the axon. The axon carries the output messages of a neuron (nerve impulses). There is only one axon per neuron, although it can branch into several axon endings. Some axons have a glial cell covering known as the myelin sheath. This fatty myelin sheath has gaps in it, revealing the bare axon, at regular intervals along the axon's length. These bare spots along the length of a myelinated axon are called nodes, or nodes of Ranvier, after their discoverer. The function of the myelin sheath and the nodes is to speed up the rate at which nerve impulses travel down the length of the axon toward their destination. The impulses sort of "jump" from node to node allowing the axon more rapid movement down the axon. This leaping of the nerve impulse from node to node is called "saltatory conduction," from the Latin "saltatore" which means to dance. Imagine the romantic image of the impulse dancing from node to node. It is extraordinary that the nodes are placed along the axon's length at just the right spatial intervals to make impulse conduction down the axon the most efficient and speedy possible. Not all axons are myelinated. Unmyelinated axons tend to be older in evolution and to be the smaller diameter axons. In these, in order to move, the nerve impulse must be regenerated at every point along the axon. This takes time and slows the conduction of the nerve impulse (called the action potential). By contrast, in myelinated axons, the impulse gets regenerated only at the bare spots on the axon, the nodes. Because the action potential gets regenerated fewer times in order to travel a given distance, than is the case for unmyelinated axons, neural conduction is faster with the insulating myelin sheath. Myelinated axons tend to be found in neural pathways mediating rapid behavior response.

The end of an axon or axon branch is called the axon bouton or simply the axon ending. Within the axon ending are structures called synaptic vescicles, which contain neurotransmitter chemicals (which have been manufactured in the soma and transported to the axon ending). When neurons communicate with one another across the synaptic gap which separates them, it is the neurotransmitter, released from the synaptic vesicles in the axon ending, that transmits the neural message. The nerve cell releasing the neurotransmitter, the sender cell, is known technically as the pre-synaptic neuron. The neuron receiving the neurotransmitter, the receiver cell, is called the post-synaptic neuron. The neurotransmitter molecules attach to special sites on the membrane of the post-synaptic neuron. These special sites are called post-synaptic receptor sites. Their shapes match the shapes of the neurotransmitter molecules they receive, a kind of "lock and key" fit.

The third part of the neuron is the dendrites, the receivers of the neuron. The post-synaptic receptor sites which receive molecules of neurotransmitter are located on the dendrites (and to a lesser degree on the soma).

The transmission of neural messages across the synaptic gap, via the release of transmitter from a pre-synaptic neuron onto post-synaptic receptor sites on a post-synaptic neuron, is called synaptic transmission or neurotransmission. Synaptic transmission is central to the brain's capacity to process information, to generate mental states, and to generate adaptive behavior.

Here is a summary of the steps in synaptic transmission.

an action potential is generated in a pre-synaptic neuron and conducted down the axon to the axon ending of that neuron arrival of the axon potential at the axon ending triggers release of transmitter from synaptic vesicles in the axon ending of this pre-synaptic neuron molecules of transmitter cross the fluid-filled synaptic space between neurons molecules of transmitter attach to post-synaptic receptor sites on the dendrite or soma of the post-synaptic neuron on the other side of the synaptic gap between pre- and post-synaptic neurons this "lock and key" interaction, between transmitter molecules and the receptor sites they attach to, causes holes or pores (ion channels) in the cell membrane to open to specific ions (electrically charged atoms) ions move across the cell membrane into the post-synaptic neuron, carrying with them their electrical charges, altering the electrical potential inside the post-synaptic neuron (this is voltage shift is called a post-synaptic potential or PSP) if the voltage shift in the post-synaptic neuron is positive and if it is large enough to reach "trigger threshold" (-55 millivolts), then an action potential is generated in the post-synaptic (receiver) neuron, which now becomes a pre-synaptic (sender) neuron for the next cell in line. Inactivation of used transmitter (by its reuptake into the pre-synaptic neuron or by its enzymatic destruction by specific enzymes)

Some of these steps require more explanation. To help you understand, we begin with a question. The question is "how do neurons produce electrical potentials such as the action potential or post-synaptic potentials?"

Neurons produce electrical potentials or voltages by electrically charged atoms called ions. These ions come mainly from dissolved salts in the body fluids inside and outside neurons. The main ions used by neurons to produce their voltages are sodium (Na+), potassium (K+), and chlorine (Cl-). Notice that the first two are positive ions and the last, chlorine ions, are negatively charged. A fourth ion, organic ions, which are large (on the molecular scale) negatively charged proteins are manufactured inside the neuron and give its voltage a negative bias. The distribution or concentrations of these ions inside and outside a neuron determine its voltage (voltage is just the physical separation of charged particles, like in a car battery with its positive and negative poles around which are concentrated positively and negatively charged particles floating in battery acid).

By these means, four main types of neuron voltages or neuron potentials are produced by neurons:

<!--[if !supportLists]-->1. <!--[endif]-->the resting potential (equal to negative 70 thousandths of a volt, -70 millivolts) <!--[if !supportLineBreakNewLine]--> <!--[endif]-->

<!--[if !supportLists]-->2. <!--[endif]-->two types of post-synaptic potentials (PSP) a) excitatory post-synaptic potentials (EPSPs)

b) inhibitory post-synaptic potentials (IPSPs) 3. the action potential (the nerve impulse)

Let's examine these potentials in more detail and see how they are produced.

THE RESTING POTENTIAL: The resting potential is sort of a baseline voltage from which the other neuron potentials are generated. It is the voltage inside a nerve cell when it is at rest, that is, it is neither receiving inputs (PSPs) at the moment nor generating any outputs (action potentials) at the moment. In this state of "rest", the voltage inside the nerve cell is -70 mv. It is negative because there are more negative ions inside the neuron when it is at rest and more positives on the outside. Specifically, there are large numbers of Na+ ions (sodium ions) outside the neuron and very few of these on the inside, when the neuron is "at rest" (when it is at resting potential). And there are more negatively charged ions inside the cell than on the outside during resting potential. This unequal distribution of ions across the cell membrane sets up the electrical "resting potential," making it equal to -70 mv.

PRODUCING OTHER NEURON POTENTIALS:

How are the other neuron potentials produced?

To get the other neuron potentials, which are just voltage shifts away from resting potential, there must occur a redistribution of ions across the cell membrane. In short, ions must move.

There are two main forces (called gradients) that can cause these ions to move.

First, opposite charges (like opposite sexes) attract one another, and like charges repel. When ions of opposite charge are unequally distributed across the cell membrane (as is the case during the resting potential), this sets up what's called a "charge gradient." If these ions are allowed to move freely, they will move along the charge gradient. Positive charges will move toward negative ones and vice versa.

Secondly, when ions of any particular type (for example, sodium ions) are unequally distributed across the cell membrane (like more Na+ outside the neuron than inside during resting potential), this sets up what's called a "concentration gradient." Such concentration gradients for several ions (sodium, potassium, and chlorine ions) exist when the neuron is at resting potential. Ions, if allowed to move freely, will move along their concentration gradients. Ions of a particular type (like Na+ ions) will move from a region of high concentration (of Na+) to a region of lower concentration (of Na+).

In short, ions, if allowed to move freely, will move along the charge gradient and along their concentration gradients. Ions "want" to move to equalize their concentrations across the cell membrane and also "want" to move to equalize the charges across the cell membrane. Though they "want" to move in these ways, they can't move when the neuron is at resting potential because the cell membrane acts as a physical barrier, preserving the unequal distributions of ions and charges, thus maintaining the concentration and charge gradients. To get ion movement, pores or ion channels in the cell membrane of the neuron "at rest" must be opened. What is it that causes the ion channels to open, allowing the ions to move along their gradients?

The arrival of transmitter molecules from the axon ending of a pre-synaptic neuron, and their attachment to post-synaptic receptor sites, is the key event. This "lock and key" interaction between molecules of transmitter and the post-synaptic receptor sites causes "doors", specific ion channels, to open. When specific ion channels (Na+ channels, for example) get opened in this way, only those specific ions (Na+, in this case) move through the cell membrane along their concentration and charge gradients. This will cause a voltage shift away from resting potential. This voltage shift is the post-synaptic potential, PSP.

POST-SYNAPTIC POTENTIALS:

The post-synaptic potentials occur in a post-synaptic neuron (thus the name), a receiver neuron. When such a neuron receives an input from a pre-synaptic neuron, in the form of transmitter molecules which attach to the post-synaptic receptor sites, ion channels then open, ions move across the cell membrane, carrying with them their electrical charges. These events change the voltage inside the post-synaptic neuron. It is this voltage shift away from resting potential that constitutes the post-synaptic potential or PSP.

An EPSP, a positive shift in voltage from the resting potential, say from -70 mv to -60 mv, occurs when Na+ channels open and Na+ ions flow into the neuron, carrying with them their positive charges, making the interior of the post-synaptic neuron more positively charged.

An IPSP, a negative shift in voltage from the resting potential, say from -70 mv to -80 mv, occurs when Cl- and K+ channels open. These ions then flow along charge and concentration gradients, which cause negatively charged Cl- ions to move in and positively charged K+ ions to move out of the post-synaptic neuron, making it more negatively charged. This increase in net negative charge inside the cell is the IPSP (inhibitory post-synaptic potential).

Note that in both the EPSP and the IPSP, it is the attachment of molecules of transmitter to post-synaptic receptor sites (like keys going into locks of a specific shape) that opens the "doors", the ion channels, allowing ions to move through the cell membrane.

But there is one more key issue here. What is it that determines which ion channels open, and therefore, whether an EPSP or an IPSP occurs? The answer is: it is the type of transmitter.

There are two basic types of neurotransmitter, excitatory and inhibitory.

Excitatory transmitters (such as acetylcholine, ACh) are those which open sodium (Na+) channels in the post-synaptic membrane, allowing sodium, carrying its positive charge, into the cell, making an EPSP.

Inhibitory transmitters (such as GABA, gamma-amino-butyric acid, or serotonin) are those which open chlorine and potassium channels in the post-synaptic membrane, allowing chlorine to follow its concentration gradient into the post-synaptic neuron and allowing potassium to follow its gradient out. These ion movements make the inside of the neuron more negative, making an IPSP.

THE ACTION POTENTIAL:

The nerve impulse, or action potential, is generated in the post-synaptic neuron only if a "trigger threshold" of -55 millivolts (minus 55 mv) is reached [your textbook states that the trigger threshold is equal to minus 65 mv. The exact voltage for trigger threshold varies from neuron to neuron and may be anywhere from minus 65 to minus 55, but will always be the same for any particular neuron. For purposes of our class, we will continue to refer to the trigger threshold of neurons as minus 55 millivolts, not minus 65 as indicated in your textbook.] When that voltage is attained, then all the sodium ion channels suddenly open, allowing a massive inflow of sodium ions, Na+, into the cell. This produces a rapid, large positive shift in the voltage of the post-synaptic neuron. This is the nerve impulse or action potential. In most neurons, it is a positive shift of about 130 millivolts, if we measure from the -70 millivolts of the resting potential, up to about a positive 60 millivolts. As fast as the voltage of the action potential rises, it starts to fall after reaching its peak. It quickly falls back to the resting potential and even a bit below resting potential (the so-called refractory period) before the return of the neuron's potential back to -70 mv. This rapid rise to the action potential's peak and then its rapid fall gives the action potential, when graphed, a spike appearance. For this reason, action potentials are often called "spikes" by neuroscientists. See the diagram of the action potential shown in your textbook to get a clearer picture of these events.

Once trigger threshold is reached and an action potential (AP) is generated, it is then conducted down the length of this neuron's axon (saltatory conduction in a myelinated axon; see above). Once the AP reaches this neuron's axon ending, its arrival causes the release of neurotransmitter molecules from the synaptic vesicles located there. Now, this neuron is no longer a post-synaptic neuron, but now it becomes a sender neuron itself, a pre-synaptic neuron (a sender neuron) with respect to the next cell in line. Its release of transmitter (step 3 in the list of 8 steps in synaptic transmission) leads to steps 4 and 5 in the list of 8 steps above and an EPSP or IPSP in the next cell in line. Remember that whether an EPSP or an IPSP is caused in the next cell in line is determined by whether an excitatory or an inhibitory transmitter has been released (see the 8 steps above).

Let's summarize the sequence of events in synaptic transmission:

AP in pre-synaptic neuron --- transmitter release --- transmitter crosses synaptic gap --- transmitter attaches to post-synaptic receptor sites --- ion channels open --- ions move --- PSP results --- if the PSP is an EPSP and if the EPSP is big enough, trigger threshold is reached in post-synaptic neuron ---post-synaptic neuron produces its own AP

These same steps are summarized in the first 7 of the 8 steps in synaptic transmission listed above. Step 8 above simply refers to the fact that after the released transmitter molecules have done their job, the used transmitter molecules must be cleaned out of the synapse. As noted above, this is accomplished by two mechanisms, reuptake and enzymatic destruction. Reuptake means that the used transmitter is reabsorbed back into the pre-synaptic ending from which it was released. Enzymatic destruction means that the used transmitter is chemically destroyed by an enzyme, and thereby inactivated.

If step 8, transmitter inactivation, didn't occur then the post-synaptic neuron would be overactivated. If this occurs on a large scale, at many synapses, behavioral and mental abnormalities will result. For example, there are some drugs (Soman, Sarin, Malathion) that block enzymatic destruction of the neurotransmitter Acetylcholine, ACh. ACh is a transmitter involved in various functions in the brain and peripheral nervous system, including stimulation of skeletal muscles, which are responsible for movement. Soman and Sarin are nerve gases. They block the enzyme acetylcholinesterase, AChE, and thereby prevent the enzymatic destruction of ACh at motor synapses which stimulate the muscles. As a result, the excess ACh at the muscles causes their overactivation. The result? Epileptic seizures so intense that death occurs. ONE FINAL POINT: There are many types of receptor for each transmitter, for example for dopamine there are D1 through D5 receptors, all for dopamine transmitter. Different receptor types for a specific transmitter may be localized in parts of the brain and may produce different effects.

NEURONS, THE MIND AND BEHAVIOR:

How do these neural processes relate to the real world of our everyday conscious experience and behavior? First of all, please understand that in complex vertebrate species, single nerve cells and their activity don't control a behavior or create a thought or a feeling. Instead, information is processed, mental states are created, and behaviors are organized by neural events (such as those described above) in complex circuits involving very large numbers of neurons. It is the interaction among huge numbers of neurons, interconnected by enormous numbers of synapses, that create our thoughts, our emotions, a memory, or a complex behavior such as human speech or the creation of a work of art.

How groups of neurons in complex circuits might produce complex things like a perception or a memory has been studied using computer modeling. Artificial neural networks are computer-based models of neural circuits and their functioning. In a computer program, artificial information processing units, called "neurodes", which are programmed to code and process information like neurons do, are interconnected into layers, which are themselves interconnected. A three-layered artificial neural network is capable of performing some very complex information processing tasks, producing responses similar to those that a real brain would produce. Furthermore, because the artificial neurodes are given, by programmers, the capability of altering the strengths or "weights" of their "synaptic connections", artificial neural networks are capable of learning when given feedback about their performance.

Given these properties, it has been shown by researchers (many of whom are at UC San Diego) that artificial neural networks can perform some of the functions of brains -- they have been shown to be able to learn patterns and regularities in inputs, to make generalizations, to form categories, and to solve complex problems.

For example, one neural network, electronically “trained-up” in principles used to find mathematical proofs, discovered a proof that had eluded human mathematicians.

Another, known as NETtalk, equipped with a voice synthesizer and photocell "eyes" learned from scratch to read and correctly pronounce written English text. It accomplished this astounding feat after only 10 hours of trial and error learning, during which it was given feedback about its attempts at pronunciation. It went through a babbling stage initially, like a child would, but soon was articulating comprehensible speech. When tested on new material, it generalized what it had learned to the new text including many new words that it had not "seen" before. An analysis by researchers of how it did this showed that it had formed categories of letters, dividing them into vowels and consonants, with rules of pronunciation for each category. It accomplished this without direct programming by humans. It extracted regularities from the words presented to it, and made generalizations, rules which it applied to new cases.

Artificial neural networks use a form of information processing called parallel distributed processing (PDP). Though these networks are not brains, they have come closer than any other computer model to simulating brain function and psychological capabilities of real brains. This suggests that brains may use PDP, carried out by PDP networks of real neurons, to produce the kinds of psychological and behavioral capacities which real brains like ours demonstrate. This is a very promising area of research being carried out in the psychology, cognitive science, and neuroscience departments at many universities worldwide.

PSYCHOACTIVE DRUGS:

Psychoactive drugs are drugs that alter the mind and behavior. If classified according to primary behavioral effects, there are five major categories.

1. CNS (central nervous system) Depressants - - these drugs reduce neural activity in the brain. Alcohol is the best known of these. Other drugs of this category (such as barbiturates, Quualudes, and benzodiazepines including Valium) also have alcohol-like affects on behavior and mental functions. At low doses of any of the drugs of this category, there is relief from anxiety. A little higher dose produces loss of social inhibitions leading to increased chances of aggression and/or sexual activity (about 50% of all murders and suicides involve use of alcohol by those involved). At a bit higher dose, drowsiness and sleep occur. Still higher doses produce anesthesia, coma, and death from respiratory failure. Respiratory failure does not occur with benzodiazepines unless they are mixed with another drug of this category. Mixing drugs increases their effects dramatically (this is called supra-additive effects) making them extra dangerous.

2. Behavioral Stimulants - - these increase neural activity in the brain; in addition several of the drugs in this category stimulate the pleasure circuits in the deeper parts of the brain. The best known stimulants include caffeine, nicotine (in cigarettes), cocaine, ecstacy, and the amphetamines. These drugs, including nicotine, are highly physically addicting. They cause changes in brain chemistry that produces a powerful need for the drug, an addiction. Amphetamines and cocaine can cause heart attack or seizures in higher doses. Also in higher doses, these two drugs can cause the symptoms of the mental disorder schizophrenia. They do this by increasing activity in nerve cells in the brain that use dopamine as their neurotransmitter, suggesting that schizophrenia involves excess dopamine nerve cell activity (this is called the dopamine hypothesis of schizophrenia).

3. Opiates - - these include morphine and all drugs that have morphine-like effects. Morphine is derived from the opium poppy. Both morphine and codeine are natural products of this plant. In addition to these opiates, there are several that are manufactured (they don't occur naturally) including heroin (which has morphine-effects, but is about 3 times as potent), Demerol, Darvon, and methadone. Morphine and other opiates suppress pain (their primary medical use), cause constipation (a secondary medical use for treatment of severe diarrhea), stimulate the pleasure circuits in the brain (the reason these drugs are sought out by illegal drug users), and depress respiration (overdoses kill you by causing your breathing to stop, after depressing the breathing centers in the medulla). In addition, codeine suppresses the cough center in the brainstem.

4. Anti-psychotic drugs - - these include the neuroleptics (anti-schizophrenic drugs, all dopamine receptor blockers) and the drugs used to treat the mood disorders--depression, and manic-depression (tricyclic anti-depressants, monoamine oxidase inhibitors, also known as MAO Inhibitors, and the Specific Serotonin Reuptake Inhibitors or SSRIs such as Prozac are all used for depression, whereas Lithium is used for manic-depression, also known as bipolar mood disorder). None of these drugs produce pleasant effects in normal persons and so are not sought out by drug users.

5. The Hallucinogens or Psychedelics--these are drugs that are characterized by their ability to produce hallucinations (false sensory experiences) and other alterations of perception, thought, and emotion. These drugs include LSD, mescaline (active ingredient in peyote), psilocybin (active ingredient in the Mexican "Magic mushrooms", THC, tetrahydrocannabinol, the active ingredient in marijuana and hashish, and very dangerous drugs such as PCP, "Deadly Nightshade," and the inhalants. These drugs are often categorized by their chemical structures according to similarities in structure to known transmitters.

Drug Tolerance, Withdrawals, and Drug Addiction:

As you continue to take any of the drugs in these first three categories, over time they become less effective and it becomes necessary to take higher and higher doses to get the same effect originally produced by the much smaller, original dose. This is called drug tolerance. It occurs for two reasons.

First, the liver gets better and better at getting rid of any particular drug as you continue to take that drug.

Second, neurons affected by the drug change their functioning in order to compensate for the presence of the drug. For example, if you have been taking a stimulant drug, the over-activation of affected neurons causes them to try to decrease their firing rates in order to counteract the stimulant effect of the drug upon them. Therefore, you must increase your dose to get the same stimulant effect you got originally from the drug. The same kind of compensation by neurons for the presence of a drug occurs with the CNS Depressants and the Opiates, as well as with the other stimulants. The real problem arises when you suddenly stop taking the drug. Your neurons have adjusted to the presence of the drug, so when you stop taking it, you suffer what's known as withdrawal symptoms.

The effects of drug withdrawal are essentially opposite to the effects originally produced by taking the drug.

For example, if you gain tolerance to a behavioral stimulant such as cocaine, then when you stop taking the cocaine, the withdrawal symptoms will be a rebound depression of the central nervous system, including depression of the pleasure circuits. The person undergoing such cocaine withdrawal will feel terribly emotionally and physically depressed. The person may feel so emotionally down, that he or she may be suicidal. Physically he or she may feel exhausted and may sleep for days straight.

Similarly, if you gain tolerance to an opiate, when you stop taking the drug you will experience withdrawal symptoms, which once again are essentially opposite to effects produced by taking an opiate. During opiate withdrawal, everything hurts intensely for no reason (stomach aches, bone aches, head aches, skin hurts, muscles ache), there is intense emotional depression, and what the literature describes as "explosive" diarrhea. Though you may wish you were dead, opiate withdrawals will not kill you.

By contrast, withdrawal from alcohol, or other CNS depressant, can kill you. Remember, withdrawal symptoms are essentially the opposite of the effects originally produced by taking the drug. CNS Depressants depress the central nervous system, so that when you withdraw from one of the drugs of this category, the brain is hyperactive to the point that hallucinations may occur (the DT's of alcoholism), there is sleeplessness and irritability, and there may be epileptic-like seizures and these can kill you.

Mechanisms of Drug Action:

How do these drugs work? In short, most psychoactive drugs produce their psychological effects by acting on one or more of the 8 steps in synaptic transmission (see above). The way a drug works on this cellular level is referred to as the drug's mechanism of action. It is possible to categorize drugs according to their mechanism of action, that is, according to how they alter synaptic transmission and which transmitter(s) they affect.

Open the attached table by clicking on the attachment at the bottom of this lecture (or if not attached here see the separate topic in this conference with the table attached to it). The attached table (here or in a separate topic in this conference) shows Mechanisms of Drug Action with some representative neurotransmitters.

Along the top of this table are listed four different transmitters (there are dozens or even hundreds). These transmitters are found in circuits in different parts of the brain and peripheral nervous system and are involved in different behavioral and mental functions. Down the left hand side of this table are 5 mechanisms of action. These are 5 different ways in which a psychoactive drug might affect synaptic transmission, and thus neural activity. In the boxes are some representative drugs. You can use this table to see which transmitter(s) are affected by a particular drug such as Heroin, and you can also see how synaptic transmission is altered at the synapses that use that transmitter(s).

For example, look at the transmitter Aceytlcholine (ACh) and go to Receptor agonists. You will see the drug Nicotine, the psychoactive ingredient in tobacco. So what this table tells you is that Nicotine is a receptor agonist at ACh synapses. Receptor agonists mimic the affected transmitter. In other words, Nicotine works on the brain by activating ACh synapses, just like the natural ACh transmitter does, but activates them when they should not be activated. This situation causes tolerance and physical drug addiction to Nicotine and its plant source, tobacco. Trying to quit cigarettes is accompanied by withdrawal symptoms, because brain chemistry has been altered by the drug. The physical addiction to Nicotine can therefore be very hard to kick. The greatest preventable cause of death in the world is cancer and heart disease caused by tobacco addiction. Ten times the number of Americans who died in the entire Vietnam War die every year from tobacco related diseases. If you smoke, try to break your addiction. You are paying to kill yourself for the financial benefit of the tobacco companies and their shareholders.

Look at the enkephalins and endorphins and look under Receptor agonists and you will see Morphine and other opiates. This tells you that these drugs work by mimicing the effects of enkephalin and endorphin transmitters, stimulating circuits which use these transmitters (pain killing circuits and pleasure circuits) when they ordinarily would not be activated. Morphine and heroin are pain killers because they activate pain-killing (analgesic) circuits in the brain.

You will notice that amphetamine and cocaine have two mechanisms of action - - both are dopamine and norepinephrine receptor agonists and both block reuptake these transmitters, increasing concentrations of these transmitters at dopamine (DA) and norepinephrine (NE) transmitters (known together as catecholamines, CA).

Look at acetylcholine and receptor blockers and you will see the drug, Curare. One place where ACh transmitter is found is at the motor neurons that stimulate muscles. Curare plugs up (like gum in the keyhole) the post-synaptic receptor sites (the "keyholes") that are on muscle cells. As a result, ACh transmitter molecules (the "keys") can't get into the receptor sites (the "keyholes") to activate them and the muscle cells where these ACh receptor sites are located. Paralysis of the muscles is the result. Curare is used by native hunters in the Amazon jungle to paralyze prey. The hunters put Curare, found in a local plant, on the tips of the darts they shoot through blowguns at their prey high in the trees. The monkey or other prey is quickly paralyzed and falls to the ground.

Now look at receptor blockers under dopamine neurotransmitter. There you find the anti-schizophrenic drugs. This shows you that all of the drugs used to treat the mental disorder, schizophrenia, are dopamine receptor blockers. This is an important piece of evidence supporting the dopamine hypothesis of schizophrenia (Schizophrenia is characterized by severe loss of contact with reality, hallucinations, delusions, illogical thought and inappropriate and inconsistent emotions. According to the dopamine hypothesis, these symptoms are due to over-activity of dopamine brain circuits).

Also under receptor blockers, but under endorphins and enkephalins (opiate-like transmitters), you will see Naloxone. This is an opiate receptor site blocker used to reverse the effects of opiate overdoses. A heroin or morphine overdose victim may be comatose and near death from respiratory failure, and yet can be brought back to normal within seconds by an injection of Naloxone (Narcan). This dramatic effect is produced when Naloxone molecules plug up opiate receptor sites preventing the opiate drug from stimulating those sites. Like magic, the opiate effects are immediately and completely reversed.

Note those drugs shown which block reuptake and block enzymatic destruction of dopamine and norepinephrine. MAO Inhibitors and Tricyclic Anti-depressants are both used to treat the mental disorder, psychotic or clinical depression (unilateral mood disorder), characterized by extreme low mood, a sense of purposelessness to life, a sense of hopelessness and extreme pessimism about one's own future, suicidal thoughts and suicide attempts. These drugs increase levels of catecholamine transmitters (DA and NE). These transmitters are found in pleasure circuits in the brain. According to the Catecholamine Theory of Mood Disorders, depression (unipolar mood disorder) is due to insufficient activity in pleasure circuits due to insufficient levels of CA transmitters. Elevations of these CA transmitters by MAO Inhibitors and Tricyclic Anti-depressants, according to this theory, increase activity in CA pleasure circuits in the brain and elevate mood as a consequence. One fact that is difficult to understand is that these drugs are effective in lifting depression only after several weeks of treatment, yet CA levels become elevated much sooner.

This ends my lecture on Biological Foundations of Mind and Behavior. I know it is a lot of material and quite technical as well. Be comforted in knowing that if you can master this material you have mastered probably the most difficult material in this course. The rest of the course material should be much easier for you. Give it your best effort. When you feel you have done so, then give it some more of your time and try to achieve real mastery of these facts. You will be rewarded for your efforts with a sense of accomplishment that you were able, by hard work, to meet a difficult challenge.