Cognitive neuroscience

Hemispheric Specialization

Lobes of the Cerebral Hemispheres

Neuronal Structure and Function

Viewing the Structures and Functions of the Brain

Postmortem Studies

Studying Live Nonhuman Animals

Studying Live Humans

Electrical Recordings

Static Imaging Techniques

Metabolic Imaging

Brain Disorders

Stroke

Brain Tumors

Head Injuries

Key Themes

Summary

Thinking about Thinking: Analytical, Creative, and Practical Questions

Key Terms

Media Resources

▪ CogLab The CogLab icon directs you to concept-related experiments and labs you can explore. Each CogLab reference includes the Lab title and number for easy access. Go to CogLab.Cengage.com.

Here are some of the questions we will explore in this chapter:

1. What are the fundamental structures and processes within the brain?

2. How do researchers study the major structures and processes of the brain?

3. What have researchers found as a result of studying the brain?

BELIEVE IT OR NOT: Does Your Brain Use Less Power Than Your Desk Lamp?

The brain is one of the premier users of energy in the human body. As much as 20% of the energy in your body is consumed by your brain, although it accounts for only about 2% of your body mass. This may come as no surprise, given that you need your brain for almost anything you do, from moving your legs to walk to reading this book, to talking to your friend on the phone. Even seeing what is right in front of your eyes takes a huge amount of processing by the brain, as you will see in Chapter 3. And yet, for all the amazing things your brain achieves, it does not use much more energy than your computer and monitor when they are “asleep.” It is estimated that your brain uses about 12 to 20 watts of power. Your sleeping computer consumes about 10 watts when it's on, and 150 watts together with its monitor or even more when it's working. Even the lamp on your desk uses more power than your brain. Your brain performs many more tasks than your desk lamp or computer. Just think about all you'd have to eat if your brain consumed as much energy as those devices (Drubach, 1999). You'll learn more about how your brain works in this chapter.

Our brains are a central processing unit for everything we do. But how do our brains relate to our bodies? Are they connected or separate? Do our brains define who we are? An ancient legend from India (Rosenzweig & Leiman, 1989) tells of Sita. She marries one man but is attracted to another. These two frustrated men behead themselves. Sita, bereft of them both, desperately prays to the goddess Kali to bring the men back to life. Sita is granted her wish. She is allowed to reattach the heads to the bodies. In her rush to bring the two men back to life, Sita mistakenly switches their heads. She attaches them to the wrong bodies. Now, to whom is she married? Who is who?

The mind-body issue has long interested philosophers and scientists. Where is the mind located in the body, if at all? How do the mind and body interact? How are we able to think, speak, plan, reason, learn, and remember? What are the physical bases for our cognitive abilities? These questions all probe the relationship between cognitive psychology and neurobiology. Some cognitive psychologists seek to answer such questions by studying the biological bases of cognition. Cognitive psychologists are especially concerned with how the anatomy (physical structures of the body) and the physiology (functions and processes of the body) of the nervous system affect and are affected by human cognition.

Cognitive neuroscience studies how the brain and other aspects of the nervous system are linked to cognitive processing and, ultimately, to behavior. The brain is the organ in our bodies that most directly controls our thoughts, emotions, and motivations (Gloor, 1997; Rockland, 2000; Shepherd, 1998). Figure 2.1 ▪ shows photos of what the brain actually looks like. We usually think of the brain as being at the top of the body's hierarchy—as the boss, with various other organs responding to it. Like any good boss, however, it listens to and is influenced by its subordinates, the other organs of the body. Thus, the brain is reactive as well as directive.

Figure 2.1 The Brain.

What does a brain actually look like? Here you can see a side view of a human brain. Subsequent figures detail some of the main features of the brain.

A major focus of brain research is localization of function. Localization of function refers to the specific areas of the brain that control specific skills or behaviors. Facts about particular brain areas and their function are interspersed throughout this chapter and also throughout the whole book.

Our exploration of the brain starts with the anatomy of the brain. We will look at the gross anatomy of the brain as well as at neurons and the ways in which information is transmitted in the brain. Then we will explore the methods scientists use to examine the brain, its structures, and its functions. And finally, we will learn about brain disorders and how they inform cognitive psychology.

Cognition in the Brain: The Anatomy and Mechanisms of the Brain

The nervous system is the basis for our ability to perceive, adapt to, and interact with the world around us (Gazzaniga, 1995b, 2000; Gazzaniga, Ivry, & Mangun, 2014). The brain is the supreme organ of the nervous system. The part of the brain that controls many of our thought processes is the cerebral cortex. Let's have a look at the structure of the brain.

Gross Anatomy of the Brain: Forebrain, Midbrain, and Hindbrain

What have scientists discovered about the human brain? The brain has three major regions: forebrain, midbrain, and hindbrain. These labels do not correspond exactly to locations of regions in an adult or even a child's head. Rather, the terms come from the front-to-back physical arrangement of these parts in the nervous system of a developing embryo. Initially, the forebrain is generally the farthest forward, toward what becomes the face. The midbrain is next in line. And the hindbrain is generally farthest from the forebrain, near the back of the neck [Figure 2.2(a) ▪]. As the fetus develops, the relative orientations change so that the forebrain is almost a cap on top of the midbrain and hindbrain. Figures 2.2(b) ▪, 2.2(c) ▪, and 2.2(d) ▪ show the changing locations and relationships of the forebrain, the midbrain, and the hindbrain over the course of development of the brain. You can see how they develop, from an embryo a few weeks after conception to birth.

▪ Figure 2.2 Fetal Brain Development.

Over the course of embryonic and fetal development, the brain becomes more highly specialized and the locations and relative positions of the hindbrain, the midbrain, and the forebrain change from conception to term.

The Forebrain

The forebrain is the region of the brain located toward the top and front of the brain. It includes the cerebral cortex, the basal ganglia, the limbic system, the thalamus, and the hypothalamus (Figure 2.3 ▪). The cerebral cortex is the outer layer of the cerebral hemispheres. It plays a vital role in our thinking and other mental processes. It therefore merits a special section in this chapter, which follows the present discussion of the major structures and functions of the brain. The basal ganglia (singular: ganglion) are collections of neurons crucial to motor function. Dysfunction of the basal ganglia can result in motor deficits. These deficits include tremors, involuntary movements, changes in posture and muscle tone, and slowness of movement. Deficits are observed in Parkinsons disease and Huntington's disease. Both of these diseases entail severe motor symptoms (Gutierrez-Garralda et al., 2013; Lerner & Riley, 2008; Lewis & Barker, 2009; Rockland, 2000).

▪ Figure 2.3 Structures of the Brain.

The forebrain, the midbrain, and the hindbrain contain structures that perform essential functions for survival and for high-level thinking and feeling.

The limbic system is important to emotion, motivation, memory, and learning. Animals such as fish and reptiles, which have relatively undeveloped limbic systems, respond to the environment almost exclusively by instinct. Mammals and especially humans have more developed limbic systems. Our limbic system allows us to suppress instinctive responses (e.g., the impulse to strike someone who accidentally causes us pain). Our limbic systems help us adapt our behaviors flexibly in response to our changing environment. The limbic system comprises three central interconnected cerebral structures: the septum, the amygdala, and the hippocampus.

The septum is involved in anger and fear (Breedlove & Watson, 2013). The amygdala plays an important role in emotion as well, especially in anger and aggression (Adolphs, 2003; Derntl et al., 2009). Stimulation of the amygdala commonly results in fear. It can be evidenced in various ways, such as through palpitations, fearful hallucinations, or frightening flashbacks in memory (Engin & Treit, 2008; Gloor, 1997; Rockland, 2000).

Damage to (lesions in) or removal of the amygdala can result in maladaptive lack of fear. In the case of lesions to the animal brain, the animal approaches potentially dangerous objects without hesitation or fear, or can no longer adequately learn fear reactions when it encounters dangerous situations (Adolphs et al., 1994; Frackowiak et al, 1997; Kazama et al, 2012). The amygdala also enhances the perception of emotional stimuli. If someone has a lesion in his or her amygdala, the perception of emotional stimuli is impaired (Anderson & Phelps, 2001; Tottenham, Hare, & Casey, 2009). For example, when people are presented with a number of words and then have to remember them, they usually remember negative words (such as murder) better than neutral words. In people with lesions to the amygdala, this is not the case. Additionally, people with autism display limited activation in the amygdala. A well-known theory of autism suggests that the disorder involves dysfunction of the amygdala, which leads to the social impairment that is typical of persons with autism, for example, difficulties in evaluating peoples trustworthiness or recognizing emotions in faces (Adolphs, Sears, & Piven, 2001; Baron-Cohen et al, 2000; Howard et al, 2000; Kleinhans et al, 2009). Two other effects of lesions to the amygdala can be visual agnosia (inability to recognize objects) and hypersexuality (Steffanaci, 1999).

The hippocampus is essential in memory formation (Eichenbaum, 1999, 2002, 2011; Gluck, 1996; Manns & Eichenbaum, 2006; O'Keefe, 2003). It gets its name from the Greek word for “seahorse,” its approximate shape. The hippocampus is essential for flexible learning, seeing relationships among items learned and spatial memory (Eichenbaum, 1997; Forcelli et al, 2014; Kaku, 2014; Squire, 1992). The hippocampus also appears to keep track of where things are and how these things are spatially related to each other. In other words, it monitors what is where (Cain, Boon, & Corcoran, 2006; Howland et al, 2008; McClelland et al, 1995; Tulving & Schacter, 1994). We return to the role of the hippocampus in Chapter 5.

People who have suffered damage to or removal of the hippocampus still can recall existing memories—for example, they can recognize old friends and places—but they are unable to form new memories (relative to the time of the brain damage). New information—new situations, people, and places—remains forever new. A disease that produces loss of memory function is Korsakoff's syndrome. Other symptoms include apathy, paralysis of muscles controlling the eye, and tremor. This loss is believed to be associated with deterioration of the hippocampus and is caused by a lack of thiamine (vitamin B-1) in the brain. The syndrome can result from excessive alcohol use, dietary deficiencies, or eating disorders.

There is a renowned case of a now-deceased patient known as H. M. (but whose real name was Henry Molaison), who after brain surgery retained his memory for events that transpired before the surgery but had no memory for events after the surgery. This case is another illustration of memory problems forming because of hippocampus damage (see Chapter 5 for more on H. M.). Disruption in the hippocampus appears to result in deficits in declarative memory (i.e., memory for pieces of information), but it does not result in deficits in procedural memory (i.e., memory for courses of action; Rockland, 2000).

The thalamus relays incoming sensory information through groups of neurons that project to the appropriate region in the cortex. Most of the sensory input into the brain passes through the thalamus, which is approximately in the center of the brain, at about eye level. To accommodate all of the types of information that must be sorted out, the thalamus is divided into a number of nuclei (groups of neurons of similar function). Each nucleus receives information from specific senses. The information is then relayed to corresponding specific areas in the cerebral cortex. The thalamus also helps in the control of sleep and waking. When the thalamus malfunctions, the result can be pain, tremor, amnesia, impairment of language, and disruptions in waking and sleeping (Cipolotti et al, 2008; Rockland, 2000; Steriade, Jones, & McCormick, 1997). In cases of schizophrenia, imaging and in vivo studies reveal abnormal changes in the thalamus (Clinton & Meador-Woodruff, 2004). These abnormalities result in difficulties in filtering stimuli and focusing attention, which in turn can explain why people suffering from schizophrenia experience symptoms such as hallucinations and delusions.

The hypothalamus regulates behavior related to species survival: fighting, feeding, fleeing, and mating. The hypothalamus also helps regulate emotions and react to stress (Malsbury, 2003). It interacts with the limbic system. The small size of the hypothalamus (from Greek hypo-, “under”; located at the base of the forebrain, beneath the thalamus) belies its importance in controlling many bodily functions (Table 2.1 ▪). The hypothalamus plays a role in sleep: Dysfunction and neural loss within the hypothalamus are noted in cases of narcolepsy, whereby a person falls asleep often and at unpredictable times (Lodi et al, 2004; Mignot, Taheri, & Nishino, 2002). The hypothalamus also is important for the functioning of the endocrine system. It is involved in stimulating the pituitary glands, through which a range of hormones are produced and released (Gazzaniga, Ivry, & Mangun, 2013).

Table 2.1 Major Structures and Functions of the Brain

Region of the Brain

Major Structures within the Regions

Functions of the Structures

Forebrain

Cerebral cortex (outer layer of the cerebral hemispheres)

Involved in

• receiving and processing sensory information,

• thinking and other cognitive processing, and

• planning and sending motor information

Basal ganglia (collections of nuclei and neural fibers)

Crucial to the function of the motor system

Limbic systems (hippocampus, amygdala, and septum)

Involved in learning, emotions, and motivation

Thalamus

Transmits sensory information coming to the cerebral cortex; includes several nuclei (groups of neurons) specializing in perception of visual stimuli, auditory stimuli, pressure and pain, and information that helps us sense physical balance and equilibrium

Hypothalamus

Involved in

• the endocrine system;

• autonomic nervous system;

• survival behavior (e.g., fighting, feeding, fleeing, and mating);

• consciousness; and

• emotions, pleasure, pain, and stress reactions

Midbrain

Superior colliculi (on top)

Involved in vision (especially visual reflexes)

Inferior colliculi (below)

Involved in hearing

Reticular activating system (also extends into the hindbrain)

Important in controlling

• consciousness (sleep arousal),

• attention,

• cardiorespiratory function, and

• movement

Gray matter, red nucleus, substantia nigra, and ventral region

Important in controlling movement

Hindbrain

Cerebellum

Essential to balance, coordination, and muscle tone

Pons (also contains part of the reticular activating system)

Involved in

• consciousness,

• facial nerves, and

• bridging neural transmissions from one part of the brain to another

Medulla oblongata

Nerves cross here from one side of the body to opposite side of the brain; involved in cardiorespiratory function, digestion, and swallowing

Structures in the forebrain, midbrain, and hindbrain perform functions essential for survival as well as for high-level thinking and feeling. For a summary of the major structures and functions of the brain, as discussed in this section, see Table 2.1.

The Midbrain

The midbrain helps to control eye movement and coordination. Table 2.1 lists several structures and corresponding functions of the midbrain. By far the most indispensable of these structures is the reticular activating system (RAS). Also called the “reticular formation,” the RAS is a network of neurons essential to regulating consciousness, including sleep; wakefulness; arousal; attention to some extent; and vital functions, such as heartbeat and breathing (Sarter, Bruno, & Berntson, 2003).

The RAS also extends into the hindbrain. Both the RAS and the thalamus are essential to our conscious awareness of or control over our existence. The hindbrain, along with the thalamus, midbrain, and hypothalamus, make up the brainstem, which connects the forebrain to the spinal cord.

Physicians make a determination of brain death based on the function of the brainstem. Specifically, a physician must determine that the brainstem has been damaged so severely that various reflexes of the head (e.g., the pupillary reflex) are absent for more than 12 hours, or the brain must show no electrical activity or cerebral circulation of blood (Berkow, 1992; Shappell et al, 2013).

The Hindbrain

The hindbrain comprises the medulla oblongata, the pons, and the cerebellum.

The medulla oblongata controls heart activity and largely controls breathing, swallowing, and digestion. The medulla is also the place at which nerves from the right side of the body cross over to the left side of the brain and nerves from the left side of the body cross over to the right side of the brain. The medulla oblongata is an elongated interior structure located at the point at which the spinal cord enters the skull and joins with the brain. The medulla oblongata, which contains part of the RAS, helps to keep us alive.

The pons contains neural fibers that pass signals from one part of the brain to another. Its name derives from the Latin for “bridge,” as it serves a bridging function. The pons also contains a portion of the RAS and nerves serving parts of the head and face. The cerebellum (from Latin, “little brain”) controls bodily coordination, balance, and muscle tone, as well as some aspects of memory involving procedure-related movements (see Chapters 7 and 8) (Middleton & Helms Tillery, 2003). The prenatal development of the human brain roughly corresponds to the evolutionary development of the human brain within the species as a whole. Specifically, the hindbrain is evolutionarily the oldest and most primitive part of the brain. It also is the first part of the brain to develop prenatally The midbrain is a relatively newer addition to the brain in evolutionary terms. It is the next part of the brain to develop prenatally. Finally, the forebrain is the most recent evolutionary addition to the brain. It is the last of the three portions of the brain to develop prenatally.

For cognitive psychologists, the most important of these evolutionary trends is the increasing neural complexity of the brain. The evolution of the human brain has offered us the enhanced ability to exercise voluntary control over behavior. It has also strengthened our ability to plan and to contemplate alternative courses of action. These ideas are discussed in the next section with respect to the cerebral cortex.

in the lab of MARTHA FARAH

Cognitive Neuroscience and Childhood Poverty

Around the time I had my daughter, I shifted my research focus to developmental cognitive neuroscience. People naturally assumed that these two life changes were related, and they were—but not in the way people thought. What captured my interest in brain development was not principally watching my daughter grow, as wondrous a process as that was. Rather, it was getting to know the babysitters who entered our lives, and learning about theirs.

These babysitters were young women of low socioeconomic status (SES), who grew up in families dependent on welfare and supported their own young children with a combination of state assistance supplemented with cash wages from babysitting. As caregivers for my child, they were not merely hired help; they were people I liked, trusted, and grew to care about. And as we became closer, and I spent more time with their families, I learned about a world very different from my own.

The children of these inner city families started life with the same evident potential as my own child, learning words, playing games, asking questions, and grappling with the challenges of cooperation, discipline, and self-control. But they soon found their way onto the same dispiriting life trajectories as their parents, with limited skills, options, hope. As a mother, I found it heartbreaking. As a scientist, I wanted to understand.

This led to a series of studies in which my collaborators and I tried first to simply document the effects of childhood poverty in terms of cognitive neuroscience's description of the mind, and then to explain the effects of poverty in terms of more specific, mechanistic causes. With Kim Noble, then a graduate student in my lab, we assessed the functioning of five different neurocognitive systems in kindergarteners of low and middle SES. We found the most pronounced effects in language and executive function systems. These results were replicated and expanded upon in additional studies with Noble and with Hallam Hurt, a pediatrician collaborator. In first graders and in middle school students, we again found striking SES disparities in language and executive function, as well as in declarative memory. Assuming that these disparities are the result of different early life experiences, what is it about growing up poor that would interfere with the development of these specific systems?

Martha Farah

In one study, we made use of data collected earlier on the middle school children just mentioned. We found that their language ability in middle school was predicted by the amount of cognitive stimulation they experienced as 4-year-olds—being read to, being taken on trips, and so on. In contrast, we found that their declarative memory ability in middle school was predicted by the quality of parental nurturance that they received as young children—being held close, being paid attention to, and so on. The latter finding might seem an odd association. Why would affectionate parenting have anything to do with memory? Yet research with animals shows that when a young animal is stressed the resulting stress hormones can damage the hippocampus, a brain area important for both stress regulation and memory. This research has also shown that more nurturing maternal behavior can buffer the young animal's hippocampus against the effects of stress. This is consistent with the hypothesis that the stressful environment of poverty affects hippocampal development, with additional help or hindrance from parenting.

My daughter is now 19, and the field of poverty neuroscience is growing up too! Many research groups are now studying SES and child development through the lens of neuroscience. Brain imaging by our group and others shows structural and functional differences in the brain. One recent study of hippocampal volume in children found SES differences and also found that these differences were attributable to stress and maternal behavior, consistent with our earlier hypothesis. Fortunately, although the developing brain is vulnerable to the effects of poverty, neuroscience tells us that the brain can change in response to positive environments at any age.

Cerebral Cortex and Localization of Function

The cerebral cortex plays an extremely important role in human cognition. It enables us to think. Because of it, we can plan, coordinate thoughts and actions, perceive visual and sound patterns, and use language. Without it, we would not be human. The cerebral cortex forms a 1- to 3-millimeter layer that wraps the surface of the brain somewhat like the bark of a tree wraps around the trunk. In human beings, the many convolutions, or creases, of the cerebral cortex include three elements. Sulci (singular: sulcus) are small grooves. Fissures are large grooves. And gyri (singular: gyrus) are bulges between adjacent sulci or fissures. These folds greatly increase the surface area of the cortex. If the wrinkly human cortex were smoothed out, it would take up about 2 square feet. The cortex makes up 80% of the human brain (Kolb & Whishaw, 1990).

The volume of the human skull has more than doubled over the past 2 million years, allowing for the expansion of the brain, and especially the cortex (Toro et al., 2008). The surface of the cerebral cortex is grayish (see also Figure 2.1). It is sometimes referred to as gray matter because it primarily includes the grayish neural-cell bodies that process the information that the brain receives and sends. In contrast, the underlying white matter of the brains interior includes mostly white, myelinated axons.

The cerebral cortex forms the outer layer of the two halves of the brain—the left and right cerebral hemispheres (Davidson & Hugdahl, 1995; Galaburda & Rosen, 2003; Gazzaniga & Hutsler, 1999; Levy, 2000). Although the two hemispheres appear to be similar, they function differently The left cerebral hemisphere is specialized for some kinds of activity, whereas the right cerebral hemisphere is specialized for other kinds. For example, receptors in the skin on the right side of the body generally send information through the medulla to areas in the left hemisphere in the brain. The receptors on the left side generally transmit information to the right hemisphere. Similarly, the left hemisphere of the brain directs the motor responses on the right side of the body. The right hemisphere directs responses on the left side of the body.

Not all information transmission is contralateral—from one side to another (contra-, “opposite”; lateral, “side”). Some ipsilateral transmission—on the same side—occurs as well. For example, odor information from the right nostril goes primarily to the right side of the brain. About half the information from the right eye goes to the right side of the brain; the other half goes to the left side of the brain. In addition to this general tendency for contralateral specialization, the hemispheres also communicate directly with one another. The corpus callosum is a dense aggregate of neural fibers connecting the two cerebral hemispheres (Witelson, Kigar, & Walter, 2003). It transmits information back and forth. Once information has reached one hemisphere, the corpus callosum transfers it to the other hemisphere. If the corpus callosum is cut, the two cerebral hemispheres—the two halves of the brain—cannot communicate with each other (Glickstein & Berlucchi, 2008). Although some functioning, such as language, is highly lateralized, most functioning—even language—depends in large part on integration of the two hemispheres of the brain. ▪ See Lab 14, Brain Asymmetry, in CogLab.

Hemispheric Specialization

How did psychologists find out that the two hemispheres have different responsibilities? The study of hemispheric specialization in the human brain can be traced back to Marc Dax, a country doctor in France. By 1836, Dax had treated more than 40 patients suffering from aphasia—loss of speech—as a result of brain damage. Dax noticed a relationship between the loss of speech and the side of the brain in which damage had occurred. In studying his patients' brains after death, Dax saw that in every case there had been damage to the left hemisphere of the brain. He was not able to find even one case of speech loss resulting from damage to the right hemisphere only.

In 1861, French scientist Paul Broca (1824–1880) claimed that an autopsy revealed that an aphasic stroke patient had a lesion in the left cerebral hemisphere of the brain. By 1864, Broca was convinced that the left hemisphere of the brain is critical in speech, a view that has held up over time. The specific part of the brain that Broca identified, now called Broca's area, contributes to speech (Figure 2.4 ▪).

Another important early researcher, German neurologist Carl Wernicke, studied language-deficient patients who could speak but whose speech made no sense. Like Broca, he traced language ability to the left hemisphere. He studied a different precise location, now known as Wernicke's area, which contributes to language comprehension (Figure 2.4).

Karl Spencer Lashley, often described as the father of neuropsychology, started studying localization in 1915. He found that implantations of crudely built electrodes in apparently identical locations in the brain yielded different results. Different locations sometimes paradoxically yielded the same results (e.g., see Lashley, 1950). Subsequent researchers, using more sophisticated electrodes and measurement procedures, have found that specific locations do correlate with specific motor responses across many test sessions. Apparently, Lashley's research was limited by the technology available to him at the time.

Despite the valuable early contributions by Broca, Wernicke, and others, the individual most responsible for modern theory and research on hemispheric specialization was Nobel Prize-winning psychologist Roger Sperry Sperry (1964) argued that each hemisphere behaves in many respects like a separate brain. In a classic experiment that supports this contention, Sperry and his colleagues severed the corpus callosum connecting the two hemispheres of a cat's brain. They then proved that information presented visually to one cerebral hemisphere of the cat was not recognizable to the other hemisphere. Similar work on monkeys indicated the same discrete performance of each hemisphere (Sperry, 1964).

Some of the most interesting information about how the human brain works, and especially about the respective roles of the hemispheres, has emerged from studies of humans with epilepsy in whom the corpus callosum has been severed. Surgically severing this neurological bridge prevents epileptic seizures from spreading from one hemisphere to another. This procedure thereby drastically reduces the severity of the seizures. However, this procedure also results in a loss of communication between the two hemispheres. It is as if the person has two separate specialized brains processing different information and performing separate functions. Patients who have undergone an operation severing the corpus callosum are called split-brain patients.

Split-brain research reveals fascinating possibilities regarding the ways we think. Many in the field have argued that language is localized in the left hemisphere. Spatial visualization ability (i.e., the ability to mentally manipulate two- or three-dimensional objects) appears to be largely localized in the right hemisphere (Farah, 1988a, 1988b; Gazzaniga, 1985). Spatial-orientation tasks also seem to be localized in the right hemisphere (Vogel, Bowers, & Vogel, 2003). It appears that roughly 90% of the adult population has language functions that are predominantly localized within the left hemisphere. There are indications, however, suggesting that the lateralization of left-handers differs from that of right-handers, and that for females, the lateralization may not be as pronounced as for males (Vogel, Bowers, & Vogel, 2003). More than 95% of right-handers and about 70% of left-handers have left-hemisphere dominance for language. In people who lack left-hemisphere processing, language development in the right hemisphere retains phonemic and semantic abilities, but it is deficient in syntactic competence (Gazzaniga & Hutsler, 1999).

The left hemisphere is important not only in language but also in movement. People with apraxia—disorders of skilled movements—often have had damage to the left hemisphere. These people have lost the ability to carry out familiar purposeful movements such as forming letters when writing by hand (Gazzaniga & Hutsler, 1999; Heilman, Coenen, & Kluger, 2008). Another role of the left hemisphere is to examine past experiences to find patterns. Finding patterns is an important step in the generation of hypotheses (Wolford, Miller, & Gazzaniga, 2000).

The right hemisphere is largely “mute” (Levy, 2000). It has little grammatical or phonetic understanding. But it does have good semantic knowledge. It also is involved in practical language use. People with right-hemisphere damage tend to have deficits in following conversations or stories. They also have difficulties in making inferences from context and in understanding metaphorical or humorous speech (Levy, 2000). The right hemisphere also plays a primary role in self-recognition. In particular, the right hemisphere seems to be responsible for identifying ones own face (Platek et al, 2004).

In studies of split-brain patients, the patient is presented with a composite photograph that shows a face that is made up of the left and right side of the faces of two different persons (Figure 2.5 ▪). They are typically unaware that they saw conflicting information in the two halves of the picture. When asked to give an answer about what they saw in words, they report that they saw the image in the right half of the picture. When they are asked to use the fingers of the left hand (which contralaterally sends and receives information to and from the right hemisphere) to point to what they saw, participants choose the image from the left half of the picture. Recall the contralateral association between hemisphere and side of the body. Given this association, it seems that the left hemisphere is controlling their verbal processing (speaking) of visual information. The right hemisphere appears to control spatial processing (pointing) of visual information. Thus, the task that the participants are asked to perform is crucial in determining what image the participant thinks was shown.

Gazzaniga (Gazzaniga & LeDoux, 1978) does not believe that the two hemispheres function completely independently but rather that they serve complementary roles. For instance, there is no language processing in the right hemisphere (except in rare cases of early brain damage to the left hemisphere). Rather, only visuospatial processing occurs in the right hemisphere. As an example, Gazzaniga has found that before split-brain surgery, people can draw three-dimensional representations of cubes with each hand (Gazzaniga & LeDoux, 1978). After surgery, however, they can draw a reasonable-looking cube only with the left hand. In each patient, the right hand draws pictures unrecognizable either as cubes or as three-dimensional objects. This finding is important because of the contralateral association between each side of the body and the opposite hemisphere of the brain. Recall that the right hemisphere controls the left hand. The left hand is the only one that a split-brain patient can use for drawing recognizable figures. This experiment thus supports the contention that the right hemisphere is dominant in our comprehension and exploration of spatial relations.

Gazzaniga (1985, 2011) has argued that the brain, and especially the right hemisphere of the brain, is organized into relatively independent functioning units that work in parallel. According to Gazzaniga, each of the many discrete units of the mind operates relatively independently of the others. These operations are often outside of conscious awareness. Although these various independent and often subconscious operations are taking place, the left hemisphere tries to assign interpretations to these operations. Sometimes the left hemisphere perceives that the individual is behaving in a way that does not intrinsically make any particular sense. For example, if you see an adult staggering along a sidewalk at night in a way that does not initially make sense, you may conclude he is drunk or otherwise not in full control of his senses. The brain thus finds a way to assign some meaning to that behavior.

In addition to studying hemispheric differences in language and spatial relations, researchers have tried to determine whether the two hemispheres think in ways that differ from one another. Levy (1974) has found some evidence that the left hemisphere tends to process information analytically (piece-by-piece, usually in a sequence). She argues that the right hemisphere tends to process it holistically (as a whole).

Lobes of the Cerebral Hemispheres

The cerebral hemispheres and cortex can be divided into four parts. They are not distinct units. Rather, they are largely arbitrary anatomical regions divided by fissures. Particular functions have been identified with each lobe, but the lobes also interact. The four lobes, named after the bones of the skull lying directly over them (Figure 2.6 ▪), are the frontal, parietal, temporal, and occipital lobes. The lobes are involved in numerous functions. Our discussion of them here describes only part of what they do.

▪ Figure 2.6 Four Lobes of the Brain.

The cortex is divided into the frontal, parietal, temporal, and occipital lobes. The lobes have specific functions but also interact to perform complex processes.

The frontal lobe, toward the front of the brain, is associated with motor processing and higher thought processes, such as abstract reasoning, problem solving, planning, and judgment (Stuss & Floden, 2003). It tends to be involved when sequences of thoughts or actions are called for. It is critical in producing speech. The prefrontal cortex, the region toward the front of the frontal lobe, is involved in complex motor control and tasks that require integration of information over time (Gazzaniga, Ivry, & Mangun, 2013).

The frontal lobe contains the primary motor cortex, which specializes in the planning, control, and execution of movement, particularly of movement involving any kind of delayed response. If your motor cortex were electrically stimulated, you would react by moving a corresponding body part. The nature of the movement would depend on where in the motor cortex your brain had been stimulated. Control of the various kinds of body movements is located contralaterally on the primary motor cortex. A similar inverse mapping occurs from top to bottom. The lower extremities of the body are represented on the upper (toward the top of the head) side of the motor cortex, and the upper part of the body is represented on the lower side of the motor cortex.

Information going to neighboring parts of the body also comes from neighboring parts of the motor cortex. Thus, the motor cortex can be mapped to show where, and in what proportions, different parts of the body are represented in the brain (Figure 2.7 ▪). Maps of this kind are called homunculi (homunculus is Latin for “little person”) because they depict the body parts of a person mapped on the brain.

The three other lobes are located farther away from the front of the head. These lobes specialize in sensory and perceptual activity.

The parietal lobe, at the upper back portion of the brain, is associated with somatosensory processing. The primary somatosensory cortex receives information from the senses about pressure, texture, temperature, and pain. It is located right behind the frontal lobe's primary motor cortex. If your somatosensory cortex were electrically stimulated, you probably would report feeling as if you had been touched. The parietal lobe also helps you perceive space and your relationship to it—how you are situated relative to the space you are occupying (Culham, 2003; Gazzaniga, Ivry, & Mangun, 2013). It is also involved in consciousness and paying attention. If you are paying attention to what you are reading, your parietal lobe is activated.

▪ Figure 2.7 Homunculus of the Primary Motor Cortex.

This map of the primary motor cortex is often termed a homunculus (from Latin, “little person”) because it is drawn as a cross section of the cortex surrounded by the figure of a small upside-down person whose body parts map out a proportionate correspondence to the parts of the cortex.

From looking at the homunculus (see Figure 2.7), you can see that the relationship of function to form applies in the development of the motor cortex. The same holds true for the somatosensory cortex regions. The greater need we have for use, sensitivity, and fine control in a particular body part, the larger the area of cortex generally devoted to that part. For example, we humans are tremendously reliant on our hands and faces in our interactions with the world. We show correspondingly large proportions of the cerebral cortex devoted to sensation in, and motor response by, our hands and face. Conversely, we rely relatively little on our toes for both movement and information gathering. As a result, the toes represent a relatively small area on both the primary motor and somatosensory cortices.

The temporal lobe is located below the parietal lobe, directly under your temples. It is associated with auditory processing (Han et al., 2011; Murray, 2003) and comprehending language. Some parts are more sensitive to sounds of higher pitch, others to sounds of lower pitch. The auditory region is primarily contralateral. Both sides of the auditory area have at least some representation from each ear. If your auditory cortex were stimulated electrically, you would report having heard some sort of sound.

The temporal lobe is also involved in retaining visual memories. For example, if you are trying to keep in memory Figure 2.6, then your temporal lobe is involved. The temporal lobe also matches new things you see to what you have retained in visual memory.

The occipital lobe is associated with visual processing (De Weerd, 2003b). The occipital lobe contains numerous visual areas, each specialized to analyze specific aspects of a scene, including color, motion, location, and form (Gazzaniga, Ivry, & Mangun, 2013). When you go to pick strawberries, your occipital lobe helps you find the red strawberries in between the green leaves.

Projection areas are the areas in the lobes in which sensory processing occurs. These areas are referred to as projection areas because the nerves contain sensory information going to (projecting to) the thalamus. It is from here that the sensory information is communicated to the appropriate area in the relevant lobe. Similarly, the projection areas communicate motor information downward through the spinal cord to the appropriate muscles via the peripheral nervous system (PNS).

The visual cortex is primarily in the occipital lobe. Some neural fibers carrying visual information travel ipsilaterally from the left eye to the left cerebral hemisphere and from the right eye to the right cerebral hemisphere. Other fibers cross over the optic chiasma (from Greek, “visual X” or “visual intersection”) and go contralaterally to the opposite hemisphere (Figure 2.8 ▪). In particular, neural fibers go from the left side of the visual field for each eye to the right side of the visual cortex. Complementarily, the nerves from the right side of each eye's visual field send information to the left side of the visual cortex.

The brain is a complex structure, and researchers use a variety of expressions to describe which part of the brain they are speaking of. Figure 2.6 explains some other words that are frequently used to describe different brain regions. These are the words rostral, ventral, caudal, and dorsal. They are all derived from Latin words and indicate the part of the brain with respect to other body parts.

▪ Figure 2.8 The Optic Tract and Pathways to the Primary Visual Cortex.

Some nerve fibers carry visual information ipsilaterally from each eye to each cerebral hemisphere; other fibers cross the optic chiasma and carry visual information contralaterally to the opposite hemisphere.

• Rostral refers to the front part of the brain (literally the “nasal region”).

• Ventral refers to the bottom surface of the body/brain (the side of the stomach).

• Caudal literally means “tail” and refers to the back part of the body/brain.

• Dorsal refers to the upside of the brain (it literally means “back,” and in animals the back is on the upside of the body).

The brain typically makes up only one-fortieth of the weight of an adult human body. Nevertheless, it uses about one-fifth of the circulating blood, one-fifth of the available glucose, and one-fifth of the available oxygen. It is the supreme organ of cognition. Understanding both its structure and function, from the neural to the cerebral levels of organization, is vital to an understanding of cognitive psychology. The recent development of the field of cognitive neuroscience, with its focus on localization of function, reconceptualizes the mind-body question discussed in the beginning of this chapter. The question has changed from “Where is the mind located in the body?” to “Where are particular cognitive operations located in the nervous system?” Throughout the text, we return to these questions in reference to particular cognitive operations and discuss these operations in more detail.

Neuronal Structure and Function

To understand how the entire nervous system processes information, we need to examine the structure and function of the cells that constitute the nervous system. Individual neural cells, called neurons, transmit electrical signals from one location to another in the nervous system (Carlson, 2006; Shepherd, 2004). The greatest concentration of neurons is in the neocortex of the brain. The neocortex is the part of the brain associated with complex cognition. It is also the part of the cerebral cortex that evolved most recently. This tissue can contain as many as 100,000 neurons per cubic millimeter (Churchland & Sejnowski, 2004). The neurons tend to be arranged in the form of networks, which provide information and feedback to each other within various kinds of information processing (Vogels, Rajan, & Abbott, 2005).

▪ Figure 2.9 The Composition of a Neuron.

The image shows a neuron with its various components. The information arrives at the dendrites and then is transferred through the axon to the terminal buttons.

Neurons vary in their structure, but almost all neurons have four basic parts, as illustrated in Figure 2.9 ▪. These include a soma (cell body), dendrites, an axon, and terminal buttons.

The soma contains the nucleus of the cell (the center portion that performs metabolic and reproductive functions for the cell). It is responsible for the life of the neuron and connects the dendrites to the axon. The dendrites are branchlike structures that receive information from other neurons, and the soma integrates the information. Learning is associated with the formation of new neuronal connections. The axon is a long, thin tube that extends (and sometimes splits) from the soma and responds to the information, when appropriate, by transmitting an electrochemical signal, which travels to the terminus (end), where the signal can be transmitted to other neurons.

Axons are of two basic, roughly equally occurring kinds, distinguished by the presence or absence of myelin. Myelin is a white, fatty substance that surrounds some of the axons of the nervous system, which accounts for some of the whiteness of the white matter of the brain. The more an axon is myelinated, the faster signals can be transmitted - the speed can reach 100 meters per second (equal to about 224 miles per hour). The myelin is distributed in segments broken up by nodes of Ranvier. Nodes of Ranvier are small gaps in the myelin coating along the axon, which increase conduction speed even more by helping to create electrical signals, also called action potentials, which are then conducted down the axon. The degeneration of myelin sheaths along axons in certain nerves is associated with multiple sclerosis, an autoimmune disease. It results in impairments of coordination and balance. In severe cases, this disease is fatal.

The terminal buttons are small knobs found at the ends of the branches of an axon that do not directly touch the dendrites of the next neuron. Rather, there is a small gap, the synapse. The synapse serves as a juncture between the terminal buttons of one or more neurons and the dendrites (or sometimes the soma) of one or more other neurons (Carlson, 2006). Synapses are important in cognition. Rats show increases in both the size and the number of synapses in the brain as a result of learning (Federmeier, Kleim, & Greenough, 2002). Decreased cognitive functioning, as in Alzheimer's disease, is associated with reduced efficiency of synaptic transmission of nerve impulses (Selkoe, 2002). Signal transmission between neurons occurs when the terminal buttons release one or more neurotransmitters at the synapse. Neurotransmitters are chemical messengers that transmit information across the synaptic gap to the receiving dendrites of the next neuron (von Bohlen und Halbach & Dermietzel, 2006).

Scientists have identified more than 100 transmitter substances, but it seems likely that more remain to be discovered. Medical and psychological researchers are working to discover and understand neurotransmitters. In particular, they wish to understand how the neurotransmitters interact with drugs, moods, abilities, and perceptions. Although we know much about the mechanics of impulse transmission in nerves, we know relatively little about how the nervous systems chemical activity relates to psychological states. Despite the limits on present knowledge, we have gained some insight into how several of these substances affect our psychological functioning.

Three types of chemical substances appear to be involved in neurotransmission:

• monoamine neurotransmitters

• amino-acid neurotransmitters

• neuropeptides

Acetylcholine is associated with memory functions, and the loss of acetylcholine through Alzheimer's disease has been linked to impaired memory functioning in Alzheimer's patients (Hasselmo, 2006). Acetylcholine also plays an important role in sleep and arousal. When someone awakens, there is an increase in the activity of so-called cholinergic neurons in the basal forebrain and the brainstem (Rockland, 2000)

Dopamine is associated with attention, learning, and movement coordination. Dopamine also is involved in motivational processes, such as reward and reinforcement. Schizophrenics show high levels of dopamine. This fact has led to the “dopamine theory of schizophrenia,” which suggests that high levels of dopamine may be partially responsible for schizophrenic conditions. Drugs used to combat schizophrenia often inhibit dopamine activity (von Bohlen und Halbach & Dermietzel, 2006).

In contrast, patients with Parkinson's disease show low dopamine levels, which leads to the typical trembling and movement problems associated with Parkinson's. When patients receive medication that increases their dopamine level, they (as well as healthy people who receive dopamine) sometimes show an increase in pathological gambling. Gambling is a compulsive disorder that results from impaired impulse control. When dopamine treatment is suspended, these patients no longer exhibit this behavior (Abler et al, 2009; Drapier et al, 2006; Voon et al, 2007). These findings support the role of dopamine in motivational processes and impulse control.

Serotonin plays an important role in eating behavior and body-weight regulation. High serotonin levels play a role in some types of anorexia. Specifically, serotonin seems to play a role in the types of anorexia resulting from illness or treatment of illness. For example, patients suffering from cancer or undergoing dialysis often experience a severe loss of appetite (Agulera et al, 2000; Davis et al, 2004). This loss of appetite is related, in both cases, to high serotonin levels. Serotonin is also involved in aggression and regulation of impulsivity (Rockland, 2000). Drugs that block serotonin tend to result in an increase in aggressive behavior.

The preceding description drastically oversimplifies the intricacies of constant neuronal communication. Such complexities make it difficult to understand what is happening in the normal brain when we are thinking, feeling, and interacting with our environment. Many researchers seek to understand the normal information processes of the brain by investigating what is going wrong in the brains of people affected by neurological and psychological disorders. In the case of depression, for example, in the early 1950s a drug (iproniazid, a monoamine oxidase inhibitor) intended to treat tuberculosis was found to have a mood-improving effect. This finding led to some early research on the chemical causes of depression. Perhaps if we can understand what has gone awry—what chemicals are out of balance—we can figure out how processes normally work and how to put things back into balance. One way of doing so might be by providing needed neurotransmitters or by inhibiting the effects of overabundant neurotransmitters.

Receptors in the brain that normally are occupied by the standard neurotransmitters can be hijacked by psychopharmacologically active drugs, legal or illegal. In such cases, the molecules of the drugs enter into receptors that normally would be for neurotransmitter substances endogenous in (originating in) the body.

CONCEPT CHECK

1. Name some of the major structures in each part of the brain (forebrain, midbrain, and hindbrain) and their functions.

2. What does localization of function mean?

3. Why do researchers believe that the brain exhibits some level of hemispheric specialization?

4. What are the four lobes of the brain and some of the functions associated with them?

5. How do neurons transmit information?

Viewing the Structures and Functions of the Brain

Scientists can use many methods for observing the human brain and theorizing how it functions. These methods include both postmortem studies and in vivo techniques. Each technique provides important information about the structure and function of the human brain. Even some of the earliest postmortem studies still influence our thinking about how the brain performs certain functions. The recent trend, however, is to focus on techniques that provide information about human mental functioning as it is occurring. This trend is in contrast to the earlier trend of waiting to find people with disorders and then studying their brains after they died. Because postmortem studies are the foundation for later work, we discuss them first. We then move on to the more modern in vivo techniques.

Postmortem Studies

Postmortem studies and brain dissections have been done for centuries. Even in the twenty-first century, researchers often use dissection to study the relation between the brain and behavior. In the ideal case, studies start during the lifetime of a person. Researchers observe and document the behavior of people who show signs of brain damage while they are alive (Wilson, 2003). Later, after the patients die, the researchers examine the patients' brains for lesions—areas where body tissue has been damaged, such as from injury or disease. Then the researchers infer that the lesioned locations maybe related to the behavior that was affected. The case of Phineas Gage, discussed in Chapter 1, was explored through these methods.

Through such investigations, researchers may be able to trace a link between an observed type of behavior and anomalies in a particular location in the brain. An early example is Broca's famous patient, Tan (so named because that was the only syllable he was capable of uttering). Tan had severe speech problems. These problems were linked to lesions in an area of the frontal lobe (Broca's area). This area is involved in certain functions of speech production. In more recent times, postmortem examinations of victims of Alzheimer's disease (an illness that causes devastating losses of memory; see Chapter 5) have led researchers to identify some of the brain structures involved in memory (e.g., the hippocampus, described earlier in this chapter). These examinations also have identified some of the microscopic aberrations associated with the disease process (e.g., distinctive tangled fibers in the brain tissue). Although lesioning techniques provide the basic foundation for understanding the relation of the brain to behavior, they are limited in that they cannot be performed on the living brain. As a result, they do not offer insights into more specific physiological processes of the brain. For this kind of information, we need to study live nonhuman animals.

Studying Live Nonhuman Animals

Scientists also want to understand the physiological processes and functions of the living brain. To study the changing activity of the living brain, scientists must use in vivo research. Many early in vivo techniques were performed exclusively on animals. For example, Nobel Prize-winning research on visual perception arose from in vivo studies investigating the electrical activity of individual cells in particular regions of the brains of animals (Hubel & Wiesel, 1963, 1968, 1979; see Chapter 3).

To obtain single-cell recordings, researchers insert a thin electrode next to a single neuron in the brain of an animal (usually a monkey or cat). They then record the changes in electrical activity that occur in the cell when the animal is exposed to a stimulus. In this way, scientists can measure the effects of certain kinds of stimuli, such as visually presented lines, on the activity of individual neurons. Neurons fire constantly, even if no stimuli are present, so the researcher must find the stimuli that produce a consistent change in the activity of the neuron. This technique can be used only in laboratory animals, not in humans, because no safe way has yet been devised to perform such recordings in humans.

A second group of animal studies includes selective lesioning—surgically removing or damaging part of the brain—to observe resulting functional deficits (Al'bertin, Mulder, & Wiener, 2003; Tee, Rajkumar, & Dawe, 2014; Mohammed, Jonsson, & Archer, 1986). Researchers recently have found neurochemical ways to induce lesions in animals' brains by administering drugs that destroy only those cells that use a particular neurotransmitter. Some drugs' effects are reversible, so that conductivity in the brain is disrupted only for a limited amount of time (Gazzaniga, Ivry, & Mangun, 2013).

A third way of conducting research with animals is by employing genetic knockout procedures. By using genetic manipulations, animals can be created without certain kinds of brain cells or receptors. Comparisons with normal animals then indicate what the function of the missing receptors or cells may be.

Studying Live Humans

Obviously, many of the techniques used to study live animals cannot be used on human participants. Therefore, generalizations to humans based on these studies are somewhat limited. However, an array of less-invasive imaging techniques for use with humans has been developed. These techniques—electrical recordings, static imaging, and metabolic imaging—are described in this section.

Electrical Recordings

The brain transmits signals through electrical potentials. When recorded, this activity appears as waves of various widths (frequencies) and heights (intensities). Electroencephalograms (EEGs) are recordings of the electrical frequencies and intensities of the living brain, typically recorded over relatively long periods (Picton & Mazaheri, 2003). Through EEGs, it is possible to study brainwave activity indicative of changing mental states such as deep sleep or dreaming. To obtain EEG recordings, electrodes are placed at various points along the surface of the scalp. The electrical activity of underlying brain areas is then recorded. The information, therefore, is not localized to specific cells. The EEG is sensitive to changes over time. For example, EEG recordings taken during sleep reveal changing patterns of electrical activity involving the whole brain. Different patterns emerge during dreaming versus deep sleep. EEGs are also used to diagnose epilepsy because they can indicate whether seizures appear in both sides of the brain at the same time, or whether they originate in one part of the brain and then spread.

To relate electrical activity to a particular event or task (e.g., seeing a flash of light or listening to sentences), EEG waves can be measured when participants are exposed to a particular stimulus. An event-related potential (ERP) is the record of a small change in the brains electrical activity in response to a stimulating event. The fluctuation typically lasts a mere fraction of a second. ERPs provide good information about the time-course of task-related brain activity. In any one EEG recording, there is a great deal of “noise”—that is, irrelevant electrical activity going on in the brain. ERPs cancel out the effects of noise by averaging out activity that is not task-related. Therefore, the EEG waves are averaged over a large number (e.g., 100) of trials to reveal the ERPs. The resulting wave forms show characteristic spikes related to the timing of electrical activity, but they reveal only general information about the location of that activity (because of low spatial resolution as a result of the placement of scalp electrodes).

The ERP technique has been used in a wide variety of studies. Some studies of mental abilities such as selective attention have investigated individual differences by using ERPs (e.g., Troche et al, 2009). ERP methods are also used to examine language processing. One study examined children who suffered from developmental language impairment and compared them with those who did not. The children were presented with pictures and a sound or word, and then had to decide whether the picture, on the one hand, and the sound or word, on the other, matched. For example, in a matching pair, a picture of a rooster would be presented with either the sound “cock-a-doodle-doo” or the spoken word “crowing.” A mismatch would be the picture of the rooster presented with the sound “ding dong” or the spoken word “chiming.” There was no difference between the two groups when they had to match the picture with the sound. The children with language impairment had greater difficulty matching the picture with the spoken word. The results confirmed the hypothesis that children with language impairment may have weak language networks (Cummings & Ceponiene, 2010).

An EEG.

ERP can be used to examine developmental changes in cognitive abilities. These experiments provide a more complete understanding of the relationship between brain and cognitive development (Taylor & Baldeweg, 2002).

The high degree of temporal resolution afforded by ERPs can be used to complement other techniques. For example, ERPs and positron emission tomography (PET) were used to pinpoint areas involved in word association (Posner & Raichle, 1994). Using ERPs, the investigators found that participants showed increased activity in certain parts of the brain (left lateral frontal cortex, left posterior cortex, and right insular cortex) when they made rapid associations to given words. As with any technique, EEGs and ERPs provide only a glimpse of brain activity. They are most helpful when used in conjunction with other techniques to identify particular brain areas involved in cognition.

Static Imaging Techniques

Psychologists use still images to reveal the structures of the brain (see Figure 2.10 ▪ and Table 2.2 ▪). The techniques include computed tomography (CT or CAT) scans, angiograms, and magnetic resonance imaging (MRI) scans. X-ray-based techniques (angiogram and CT scan) allow for the observation of large abnormalities of the brain, such as damage resulting from strokes or tumors. They are limited in their resolution, however, and cannot provide much information about smaller lesions and aberrations.

▪ Figure 2.10 Brain Imaging Techniques.

Various techniques have been developed to picture the structures—and sometimes the processes—of the brain.

Unlike conventional X-ray methods that only allow a two-dimensional view of an object, a CT scan consists of several X-ray images of the brain taken from different vantage points that, when combined, result in a three-dimensional image.

The aim of an angiography is not to look at the structures in the brain, but rather to examine the blood flow. When the brain is active, it needs energy, which is transported to the brain in the form of oxygen and glucose by means of the blood. In angiography, a dye is injected into an artery that leads to the brain, and then an X-ray image is taken. The image shows the circulatory system, and it is possible to detect strokes (disruption of the blood flow often caused by the blockage of the arteries through a foreign substance) or aneurysms (abnormal ballooning of an artery), or arteriosclerosis (a hardening of arteries that makes them inflexible and narrow).

Table 2.2 Cognitive Neuropsychological Methods for Studying Brain Functioning

Method

Procedure

Suitable for Humans?

Advantages

Disadvantages

Single-cell recording

Thin electrode is inserted next to a single neuron. Changes in electrical activity occurring in the cell are then recorded.

No

Rather precise recording of electrical activity

Cannot be used with humans

Electroencephalograms (EEG)

Changes in electrical potentials are recorded via electrodes attached to scalp.

Yes

Relatively noninvasive

Imprecise

Event-related potential (ERP)

Changes in electrical potentials are recorded via electrodes attached to scalp.

Yes

Relatively noninvasive

Does not show actual brain images

Positron emission tomography (PET)

Participants ingest a mildly radioactive form of oxygen that emits positrons as it is metabolized. Changes in concentration of positrons in targeted areas of the brain are then measured.

Yes

Shows images of the brain in action

Less useful for fast processes

Functional magnetic resonance imaging (fMRI)

Creates a magnetic field that induces changes in the particles of oxygen atoms. More active areas draw more oxygenated blood than do less active areas in the brain. The differences in the amounts of oxygen consumed form the basis for fMRI measurements.

Yes

Shows images of the brain in action; more precise than PET

Requires individual to be placed in uncomfortable scanner for some time

Transcranial magnetic stimulation (IMS)

Involves placing a coil on a person's head and then allowing an electrical current to pass through it. The current generates a magnetic field. This field disrupts the small area (usually no more than a cubic centimeter) beneath it. The researcher can then look at cognitive functioning when the particular area is disrupted.

Yes

Enables researcher to pinpoint how disruption of a particular area of brain affects cognitive functioning

Potentially dangerous if misused

Magnetoencephalography (MEG)

Involves measuring brain activity through detection of magnetic fields by placing a device over the head.

Yes

Extremely precise spatial and temporal resolution

Requires expensive machine not readily available to researchers

Functional transcranial Doppler sonography (fTCD)

Ultrasound measures the velocity of blood flow in the brain.

Yes

Excellent temporal resolution, suitable for children

Limited spatial resolution

Near-infrared spectroscopy (NIRS)

A sensor on the forehead measures blood flow in the prefrontal cortex and amount of oxygen in the blood.

Yes

Portable, inexpensive, suitable for children

Instruments need to be finely tuned and sensitive

The MRI scan is of great interest to cognitive psychologists (Figure 2.11 ▪). The MET reveals high-resolution images of the structure of the living brain by computing and analyzing magnetic changes in the energy of the orbits of nuclear particles in the molecules of the body. There are two kinds of MRIs: structural MRIs and functional MRIs. Structural MRIs provide images of the brains size and shape, whereas functional MRIs visualize the parts of the brain that are activated when a person is engaged in a particular task. MRIs allow for a much clearer picture of the brain than CT scans. A strong magnetic field is passed through the brain of a patient. A scanner detects various patterns of electromagnetic changes in the atoms of the brain. These molecular changes are analyzed by a computer to produce a three-dimensional picture of the brain. This picture includes detailed information about brain structures. For example, MRI has been used to show that musicians who play string instruments such as the violin or the cello tend to have an expansion of the brain in an area of the right hemisphere that controls left-hand movement (because control of hands is contralateral, with the right side of the brain controlling the left hand, and vice versa; Munte, Altenmuiler, & Jancke, 2002). We tend to view the brain as controlling what we can do. This study is a good example of how what we do—our experience—can affect the development of the brain.

MRI also facilitates the detection of lesions, such as lesions associated with particular disorders of language use, but it does not provide much information about physiological processes. The two techniques discussed in the following section, however, do provide such information.

▪ Figure 2.11 Magnetic Resonance Imaging (MRI).

An MRI machine can provide data that show which areas of the brain are involved in different kinds of cognitive processing.

Metabolic Imaging

Metabolic imaging techniques rely on changes that take place within the brain as a result of increased consumption of glucose and oxygen in active areas of the brain (Baars & Gage, 2012). The basic idea is that active areas in the brain consume more glucose and oxygen than do inactive areas during some tasks. An area specifically required by one task ought to be more active during that task than during more generalized processing and thus should require more glucose and oxygen (Purves, Cabeza, Huettel, LaBar, Piatt, & Woldorff, 2012). Scientists attempt to pinpoint specialized areas for a task by using the subtraction method. This method uses two different measurements: one that was taken while the subject was involved in a more general or control activity, and one that was taken when the subject was engaged in the task of interest. The difference between these two measurements equals the additional activation recorded while the subject is engaged in the target task as opposed to the control task. The subtraction method thus involves subtracting activity during the control task from activity during the task of interest. The resulting difference in activity is analyzed statistically. This analysis determines which areas are responsible for performance of a particular task above and beyond the more general activity. For example, suppose the experimenter wishes to determine which area of the brain is most important for retrieval of word meanings. The experimenter might subtract activity during a task involving reading of words from activity during a task involving the physical recognition of the letters of the words. The difference in activity would be presumed to reflect the additional resources used in retrieval of meaning.

There is one important caveat to remember about these techniques: Scientists have no way of determining whether the net effect of this difference in activity is excitatory or inhibitory (because some neurons are activated by, and some are inhibited by, other neurons' neurotransmitters). Therefore, the subtraction technique reveals net brain activity for particular areas. It cannot show whether the area's effect is positive or negative. Moreover, the method assumes that activation is purely additive—that it can be discovered through a subtraction method without taking into account interactions among elements.

This description greatly oversimplifies the subtraction method. But it shows at a general level how scientists assess physiological functioning of particular areas using imaging techniques.

PET scans measure increases in oxygen consumption in active brain areas during particular kinds of information processing (O'Leary et al, 2007; Raichle, 1998, 1999). To track their use of oxygen, participants are given a mildly radioactive form of oxygen that emits positrons as it is metabolized (positrons are particles that have roughly the same size and mass as electrons, but that are positively rather than negatively charged). Next, the brain is scanned to detect positrons. A computer analyzes the data to produce images of the physiological functioning of the brain in action.

PET scans can assist in the diagnosis of disorders of cognitive decline such as Alzheimer's by searching for abnormalities in the brain (Jack, Barrio, & Kepe, 2013; Patterson et al, 2009). PET scans have been used to show that blood flow increases to the occipital lobe of the brain during visual processing (Nakamura et al, 2000; Posner et al, 1988). PET scans also are used for comparatively studying the brains of people who score high versus low on intelligence tests. When high-scoring people are engaged in cognitively demanding tasks, their brains seem to use glucose more efficiently—in highly task-specific areas of the brain. The brains of people with lower scores appear to use glucose more diffusely, across larger regions of the brain (Haier et al, 1992). Likewise, a study has shown that Broca's area as well as the left anterior temporal area and the cerebellum are involved in the learning of new words (Groenholm et al, 2005).

PET scans have been used to illustrate the integration of information from various parts of the cortex (Castelli et al, 2005; Posner et al, 1988). Specifically, PET scans were used to study regional cerebral blood flow during several activities involving the reading of single words. When participants looked at a word on a screen, areas of their visual cortex showed high levels of activity. When they spoke a word, their motor cortex was highly active. When they heard a word spoken, their auditory cortex was activated. When they produced words related to the words they saw (requiring high-level integration of visual, auditory, and motor information), the relevant areas of the cortex showed the greatest amount of activity.

PET scans are not highly precise because they require a minimum of about half a minute to produce data regarding glucose consumption. If an area of the brain shows different amounts of activity over the course of time measurement, the activity levels are averaged, potentially leading to conclusions that are less than precise.

Functional magnetic resonance imaging (fMRI) is a neuroimaging technique that uses magnetic fields to construct a detailed representation in three dimensions of levels of activity in various parts of the brain at a given moment in time. This technique builds on MRI, but it uses increases in oxygen consumption to construct images of brain activity. The basic idea is the same as in PET scans, but the fMRI technique does not require the use of radioactive particles. Rather, the participant performs a task while placed inside an MRI machine. This machine typically looks like a tunnel. When someone is wholly or partially inserted in the tunnel, he or she is surrounded by a doughnut-shaped magnet. An fMRI creates a magnetic field that induces changes in the particles of oxygen atoms. More active areas draw more oxygenated blood than do less active areas in the brain. So shortly after a brain area has been active, a reduced amount of oxygen should be detectable in this area. This observation forms the basis for fMRI measurements. These measurements then are computer analyzed to provide the most precise information currently available about the physiological functioning of the brains activity during task performance.

This technique is less invasive than PET. It also has higher temporal resolution—measurements can be taken for activity lasting fractions of a second, rather than only for activity lasting minutes to hours. One major drawback is the expense of fMRI. Relatively few researchers have access to the required machinery and testing of participants is time consuming.

The fMRI technique can identify regions of the brain active in many areas, such as vision (Engel et al, 1994; Kitada et al, 2010), attention (Cohen et al, 1994; Samanez-Larkin et al, 2009), language (Gaillard et al, 2003; Stein et al., 2009), and memory (Gabrieli et al, 1996; Wolf, 2009). For example, fMRI has shown that the lateral prefrontal cortex is essential for working memory. This is a part of memory that processes information that is actively in use at a given time (McCarthy et al, 1994). Also, fMRI methods are used to examine brain changes in specific patient populations, including people with schizophrenia and epilepsy (Detre, 2004; Weinberger et al, 1996).

A related procedure is pharmacological MRI (phMRI). The phMRI combines fMRI methods with the study of psychopharmacological agents. These studies examine the influence and role of particular psychopharmacological agents on the brain. PhMRIs have been used to examine the role of agonists (which strengthen responses) and antagonists (which weaken responses) on the same receptor cells. These studies have allowed for the examination of drugs used for treatment. The investigators can predict the responses of patients to neurochemical treatments through examination of the persons brain makeup. Overall, these methods aid in the understanding of brain areas and the effects of psychopharmacological agents on brain functioning (Baliki et al, 2005; Easton et al, 2007; Honey & Bullmore, 2004; Kalisch et al., 2004).

Another procedure related to fMRI is diffusion tensor imaging (DTI). DTI examines the restricted dispersion of water in tissue and, of special interest, in axons. Water in the brain cannot move freely, but rather, its movement is restricted by the axons and their myelin sheaths. DTI measures how far protons have moved in a particular direction within a specific time interval. This technique has been useful in the mapping of the white matter of the brain and in examining neural circuits. Some applications of this technique include examination of traumatic brain injury, schizophrenia, brain maturation, and multiple sclerosis (Ardekani et al., 2003; Beyer, Ranga, & Krishnan, 2002; Cookey, Bernier, & Tibbo, 2014; Ramachandra et al., 2003; Sotak, 2002; Sundgren et al., 2004).

A recently developed technique for studying brain activity bypasses some of the problems with other techniques (Walsh & Pascual-Leone, 2005). Transcranial magnetic stimulation (TMS) temporarily disrupts the normal activity of the brain in a limited area. Therefore, it can imitate lesions in the brain or stimulate brain regions. TMS requires placing a coil on a persons head and then allowing an electrical current to pass through it (Figure 2.10). The current generates a magnetic field. This field disrupts the small area (usually no more than a cubic centimeter) beneath it. The researcher can then look at cognitive functioning when the particular area is disrupted. This method is restricted to brain regions that lie close to the surface of the head. An advantage to TMS is that it is possible to examine causal relationships with this method because the brain activity in a particular area is disrupted and then its influence on task-performance is observed; most other methods allow the investigator to examine only correlational relationships by the observation of brain function (Gazzaniga, Ivry, & Mangun, 2013; Gazzaniga & Mangun, 2014). TMS has been used, for example, to produce “virtual lesions” and investigate which areas of the brain are involved when people grasp or reach for an object (Koch & Rothwell, 2009). It is even hypothesized that repeated magnetic impulses (rTMS) can serve as a therapeutic means in the treatment of neuropsychological disorders such as depression or anxiety disorders (Pallanti & Bernardi, 2009).

Magnetoencephalography (MEG) measures brain activity from outside the head (similar to EEG) by picking up magnetic fields emitted by changes in brain activity. This technique allows localization of brain signals so that it is possible to know what different parts of the brain are doing at different times. It is one of the most precise of the measuring methods. MEG is used to help surgeons locate pathological structures in the brain (Baumgartner, 2000). A recent application of MEG involved patients who reported phantom limb pain. In cases of phantom limb pain, a patient reports pain in a body part that has been removed, for example, a missing foot. When certain areas of the brain are stimulated, phantom limb pain is reduced. MEG has been used to examine the changes in brain activity before, during, and after electrical stimulation. These changes in brain activity corresponded with changes in the experience of phantom limb pain (Kringel-bach et al., 2007).

A number of other techniques recently have been developed. One problem that researchers had in the past was that they could locate which parts of the brain are active in a given task by using fMRI and look at the exact timing of processes in the brain using MEG, but it was hard to find a technique that combined the advantages of both techniques. In 2014, researchers at Massachusetts Institute of Technology (MIT) combined the time and location information gained by those two methods by integrating the results using a special computational technique. Thus, in the future, questions about when and where the brain processes visual information will be addressed in more detail (Cichy, Pantazis, & Oliva, 2014).

Functional transcranial Doppler sonography (fTCD).

Another technology that only recently has been developed is functional transcranial Doppler sonography (fTCD). It uses ultrasound technology to track the velocity of blood flow in the brain. Because the blood flow can be monitored on a continuous basis, the resolution of fTCD is superior to techniques such as PET. It is noninvasive and easy to use, which makes it a good technique to use on children or people who have trouble cooperating with instructions (Lohmann, Ringelstein, & Knecht, 2006).

Near-infrared spectroscopy (NIRS), another technique developed rather recently, can monitor blood flow in the prefrontal cortex. It also can monitor the amount of oxygen in the blood. A sensor is attached to a persons forehead and measurements are taken, usually before, during, and after performing a task. Because attaching the sensor to the forehead is relatively easy and the subject can still move around within limits, this is another technique that works particularly well with children. Also, the instruments are portable for use in a variety of settings.

Current techniques still do not provide unambiguous mappings of particular functions to particular brain structures, regions, or even processes. Rather, some discrete structures, regions, or processes of the brain appear to be involved in particular cognitive functions. Our current understanding of how particular cognitive functions are linked to particular brain structures or processes allows us only to infer suggestive indications of some kind of relationship. Through sophisticated analyses, we can infer increasingly precise relationships. But we are not yet at a point at which we can determine the specific cause-effect relationship between a given brain structure or process and a particular cognitive function because particular functions may be influenced by multiple structures, regions, or processes of the brain. Finally, these techniques provide the best information only in conjunction with other experimental techniques for understanding the complexities of cognitive functioning. These combinations generally are completed with human participants, although some researchers have combined in vivo studies in animals with brain-imaging techniques (Dedeogle et al., 2004; Kornblum et al, 2000; Logothetis, 2004).

CONCEPT CHECK

1. In the investigation of the structure and functions of the brain, what methods of study can be used only in nonhuman animals, and what methods can be used in humans?

2. What are typical questions that are investigated with EEGs, PETs, and fMRIs?

3. Why is it useful to have imaging methods that display the metabolism of the brain?

4. What are the advantages and disadvantages of in vivo techniques compared with postmortem studies?

Brain Disorders

A number of brain disorders can impair cognitive functioning. Brain disorders can give us valuable insight into the functioning of the brain. As mentioned previously, scientists often write detailed notes about the condition of a patient and analyze the brain of a patient once the patient has died to see which areas in the brain may have caused the symptoms the patient experienced. Furthermore, with the in vivo techniques that have been developed over the past decades, many tests and diagnostic procedures can be executed during the lifetime of a patient to help ease patient symptoms and to gain new insight into how the brain works.

Stroke

Vascular disorder is a brain disorder caused by a stroke. Strokes occur when the flow of blood to the brain undergoes a sudden disruption. People who experience stroke typically show marked loss of cognitive functioning. The nature of the loss depends on the area of the brain that is affected by the stroke. The person may experience paralysis, pain, numbness, a loss of speech, a loss of language comprehension, impairments in thought processes, a loss of movement in parts of the body, or other symptoms.

Two kinds of stroke may occur (NINDS Stroke Information, 2009). An ischemic stroke usually occurs when a buildup of fatty tissue occurs in blood vessels over a period of years, and a piece of this tissue breaks off and gets lodged in arteries of the brain. Ischemic strokes can be treated by clot-busting drugs. The second kind of stroke, a hemorrhagic stroke, occurs when a blood vessel in the brain suddenly breaks. Blood then spills into surrounding tissue. As the blood spills over, brain cells in the affected areas begin to die. This death is either from the lack of oxygen and nutrients or from the rupture of the vessel and the sudden spilling of blood. The prognosis for stroke victims depends on the type and severity of damage. Symptoms of stroke appear immediately on the occurrence of stroke.

Typical symptoms include the following (NINDS Stroke Information, 2009):

• numbness or weakness in the face, arms, or legs (especially on one side of the body)

• confusion and difficulty speaking or understanding speech

• vision disturbances in one or both eyes

• dizziness, trouble walking, or loss of balance or coordination

• severe headache with no known cause

BELIEVE IT OR NOT: Brain Surgery Can Be Performed While You Are Awake!

Can you imagine having major surgery performed on you while you are awake? It's possible, and indeed sometimes it is done. When patients who have brain tumors or who suffer from epilepsy receive brain surgery, they are often woken up from the anesthesia after the surgeons have opened their skull and exposed the brain. This way the surgeons can talk to the patient and perform tests by stimulating the patient's brain to map the different areas of the brain that control important functions such as vision or memory. The brain itself lacks pain receptors, and when doctors stimulate a patient's brain during open-brain surgery while the patient is awake, the patient does not feel any pain. You can nevertheless get a headache, but that is because the tissue and nerves that surround the brain are sensitive to pain, not the brain itself. The communication with the patient enhances the safety and precision of the procedure as compared with brain surgery that is performed solely on the basis of brain scans that were performed using imaging technologies discussed in this chapter.

Brain Tumors

Brain tumors, also called neoplasms, can affect cognitive functioning in serious ways. Tumors can occur in either the gray or the white matter of the brain. Tumors of the white matter are more common (Gazzaniga, Ivry & Mangun, 2009).

Two types of brain tumors can occur. Primary brain tumors start in the brain. Most childhood brain tumors are of this type. Secondary brain tumors start as tumors somewhere else in the body, such as in the lungs. Brain tumors can be either benign or malignant. Benign tumors do not contain cancer cells. They typically can be removed and will not grow back. Cells from benign tumors do not invade surrounding cells or spread to other parts of the body. If, however, they press against sensitive areas of the brain, they can result in serious cognitive impairments. They also can be life-threatening, unlike benign tumors in most other parts of the body. Malignant brain tumors, unlike benign ones, contain cancer cells. They are more serious and usually threaten the victims life. They often grow quickly. They tend to invade surrounding healthy brain tissue. In rare instances, malignant cells may break away and cause cancer in other parts of the body. Following are the most common symptoms of brain tumors (What You Need to Know about Brain Tumors, 2009):

• headaches (usually worse in the morning)

• nausea or vomiting

• changes in speech, vision, or hearing

• problems balancing or walking

• changes in mood, personality, or ability to concentrate

• problems with memory

• muscle jerking or twitching (seizures or convulsions)

• numbness or tingling in the arms or legs

The diagnosis of brain tumor typically is made through neurological examination, CT scan, or MM. The most common form of treatment is a combination of surgery, radiation, and chemotherapy.

Head Injuries

Head injuries result from many causes, such as a car accident, contact with a hard object, or a bullet wound. Head injuries are of two types. In closed-head injuries, the skull remains intact, but there is damage to the brain, typically from the mechanical force of a blow to the head. Slamming ones head against a windshield in a car accident might result in such an injury. In open-head injuries, the skull does not remain intact but rather is penetrated, for example, by a bullet.

Head injuries are surprisingly common. Roughly 1.4 million North Americans suffer such injuries each year. About 50,000 of them die, and 235,000 need to be hospitalized. About 2% of the U.S. population needs long-term assistance in their daily living because of head injuries (National Center for Injury Prevention and Control, 2009b). Snowboarder Kevin Pearce sustained a traumatic brain injury while training for the 2010 winter Olympic Games in Vancouver. He spent almost a month in intensive care and then spent another three months in hospital rehabilitation, needing to learn again how to walk and speak. His recovery continues even years after the accident. He has shifted his career from snowboarding to educating the public about brain injuries and raising money to improve the lives of those affected by brain injuries.

Loss of consciousness is a sign that there has been some degree of damage to the brain as a result of the injury. Damage resulting from head injury can include spastic movements, difficulty in swallowing, and slurring of speech, among many other cognitive problems. Immediate symptoms of a head injury include the following (National Center for Injury Prevention and Control, 2009a):

• abnormal breathing

• disturbance of speech or vision

• pupils of unequal size

• weakness or paralysis

• dizziness

• neck pain or stiffness

Cognitive symptoms can vary widely, depending on the area of the brain that is affected. Patients may experience concentration problems, may have difficulty understanding others or speaking and putting their own thoughts in words, may find it hard to understand abstract concepts, or may have trouble remembering things.

CONCEPT CHECK

1. Why is the study of brain disorders useful for cognitive psychologists?

2. What are brain tumors, and how are they diagnosed?

3. What are the causes of strokes?

4. What are some of the symptoms of head injuries?

Key Themes

In Chapter 1, we reviewed seven key themes that pervade cognsitive psychology. Several of them are relevant here.

Biological versus behavioral methods. The mechanisms and methods described in this chapter are primarily biological. And yet, a major goal of biological researchers is to discover how cognition and behavior relate to these biological mechanisms. For example, they study how the hippocampus enables learning. Thus, biology, cognition, and behavior work together. They are not in any way mutually exclusive. They answer related, but not identical, questions (Uttal, 2014).

Nature versus nurture. One comes into the world with many biological structures and mechanisms in place. But nurture acts to develop them and enable them to reach their potential. The existence of the cerebral cortex is a result of nature, but the memories stored in it derive from nurture. As stated in Chapter 1, nature does not act alone. Rather, its marvels unfold through the interventions of nurture.

Applied versus basic research. Much of the research in biological approaches to cognition is basic. But this basic research later enables us, as cognitive psychologists, to make applied discoveries. For example, to understand how to treat and, hopefully, help individuals with brain damage, cognitive neuropsychologists first must understand the nature of the damage and its pervasiveness. Many modern antidepressants, for example, affect the reuptake of serotonin in the nervous system. By inhibiting reuptake, they increase serotonin concentrations and ultimately increase feelings of well-being. Interestingly, applied research can help basic research as much as basic research can help applied research. In the case of antidepressants, scientists knew the drugs worked before they knew exactly how they worked. Applied research in creating the drugs helped the scientists understand the biological mechanisms underlying the success of the drugs in relieving symptoms of depression.

SUMMARY

1. What are the fundamental structures and processes within the brain? The nervous system, governed by the brain, is divided into two main parts: the central nervous system, consisting of the brain and the spinal cord, and the peripheral nervous system, consisting of the rest of the nervous system (e.g., the nerves in the face, legs, arms, and viscera).

2. How do researchers study the major structures and processes of the brain? For centuries, scientists have viewed the brain by dissecting it. Modern dissection techniques include the use of electron microscopes and sophisticated chemical analyses to probe the mysteries of individual cells of the brain. Additionally, surgical techniques on animals (e.g., the use of selective lesioning and single-cell recording) often are used. On humans, studies have included electrical analyses (e.g., electroencephalograms and event-related potentials), studies based on the use of X-ray techniques (e.g., angiograms and computed tomograms), studies based on computer analyses of magnetic fields within the brain (magnetic resonance imaging), and studies based on computer analyses of blood flow and metabolism within the brain (positron emission tomography and functional magnetic resonance imaging) (Sousa, 2011).

3. What have researchers found as a result of studying the brain? The major structures of the brain may be categorized as those in the forebrain (e.g., the all-important cerebral cortex and the thalamus, the hypothalamus, and the limbic system, including the hippocampus), the midbrain (including a portion of the brainstem), and the hindbrain (including the medulla oblongata, the pons, and the cerebellum). The highly convoluted cerebral cortex surrounds the interior of the brain and is the basis for much of human cognition. The cortex covers the left and right hemispheres of the brain. They are connected by the corpus callosum. In general, each hemisphere contralaterally controls the opposite side of the body. Based on extensive split-brain research, many investigators believe that the two hemispheres are specialized: In most people, the left hemisphere primarily controls language. The right hemisphere primarily controls visuospatial processing. The two hemispheres also may process information differently.

Another way to view the cortex is to identify differences among four lobes. Roughly speaking, higher thought and motor processing occur in the frontal lobe. Somatosensory processing occurs in the parietal lobe. Auditory processing occurs in the temporal lobe, and visual processing occurs in the occipital lobe. Within the frontal lobe, the primary motor cortex controls the planning, control, and execution of movement. Within the parietal lobe, the primary somatosensory cortex is responsible for sensations in our muscles and skin. Specific regions of these two cortices can be mapped to particular regions of the body.