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Learning Objectives

After reading this chapter, you should be able to:

• Identify the contributions of some of the early contributors, such as Donald Hebb, to our understanding of neuroscience.

• Describe how temperamental variation reflects our neurobiological endowment.

• Discuss how various neurobiological models of personality use neurotransmitter systems to explain variations in personality.

• Characterize the role of serotonin in depres- sion and the controversy associated with the placebo effect.

• Explain how early trauma may impact neurobiological functions and lead to personality changes.

• Describe the degree to which research- ers believe personality characteristics are heritable.

• Explain how genes and the environment inter- act to determine phenotypic expression.

Neurobiological Models of Personality 4

Chapter Outline Introduction

4.1 Neuroscience and Personality

4.2 An Overview of the Nervous System • The Nervous System • Neurons—The Building Blocks of the Brain • Neurotransmitters • Structural Organization of the Brain • Specialization of the Brain

4.3 Using Neuroscience to Inform Our Understanding of Human Behavior • The Brain and Personality • Dreaming • The Unconscious • The Fight or Flight Response • Attachment and Separation • Stress Response Syndrome and Emotional

Trauma

• Describe what we have learned from twin studies and how recent work has begun to examine the contributing role of the pre-birth environment (placenta/chorion).

• Describe the emerging field of epigenetics and explain how epigenetic processes can impact the development of personality.

• Characterize how neuroscience has merged with other sub-disciplines in psychology to further our understanding in those areas.

• Identify some of the commonly employed methods of assessment in the field of neuroscience.

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CHAPTER 4

Introduction During the fall season, most of us will face the decision to either get immunized for the flu or not. Some are diligent about doing so every year, despite the fact that the flu shot will not protect them against all flu viruses (just those estimated to be most prevalent that year). Others opt against doing so, sometimes for reasons as simple as not perceiving themselves to have sufficient time to stop by a phar- macy or doctor’s office. Although this decision may appear trivial, for someone who is pregnant (especially in the early stages), the decision may have tremen- dous implications for the unborn child and his or her life trajectory. During early fetal development, neurogenesis (the creation of new neurons) is near its peak, with estimates of approximately three million new neurons developing per min- ute (Purves & Lichtman, 1985). Because this is such a critical period of develop- ment and tremendous growth, it is not surprising to find that exposure to viruses during this developmental period can be especially problematic for the fetus. For example, research suggests that women who contract influenza during pregnancy will have children with a significantly higher chance of developing schizophrenia later in life (e.g., Brown, 2006). Recent large-scale genetic studies have uncovered

Introduction

4.4 Temperamental Substrate of Personality • Thomas and Chess’s Classification of

Temperament

4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models • Eysenck’s Three-Factor Model • Buss and Plomin’s Model • Depue’s Three-Factor Model • Cloninger’s Unified Biosocial Theory of

Personality • Siever’s Dimensional Model • Application of Neurobiological Models

4.6 Studying the Genetic Basis of Human Behavior and Personality • Considering the Chorionic Status of

Monozygotic Twins • Molecular Genetics and Personality • Converging Branches of Neuroscience • Emerging Branches of Neuroscience:

Epigenetics • Contributions Beyond Psychology and

Future Directions

4.7 Assessment Methods in Neurobiological Psychology • Electrical Stimulation of the Brain • Single-Cell Recording • Neuroanatomical Studies • Brain Lesioning and Functional

Neurosurgery • Case Studies of Neurological Disorders • Neuropsychological Testing • Electroencephalography (EEG) and

Neuroimaging • Current Challenges and Future Direc-

tions in Neurobiological Assessments

Summary

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CHAPTER 4 4.1 Neuroscience and Personality

strong evidence for numerous other neurobiological/genetic risk factors for the development of schizophrenia, all of which play an important role in the mani- festation of this disease (e.g., Bray, Leweke, Kapur, & Meyer-Lindenberg, 2010). What this illustration suggests is the potential dramatic impact of neurobiological factors on later life functioning.

Can we accurately predict the impact of neurobiological factors through genetic mapping or advanced imaging techniques? Are any of these neurobiological fac- tors alterable, and how are they expressed genetically? How strong are the asso- ciations between neurobiology and personality variables? The current chapter will consider these questions, after first introducing the field of neuroscience and some of the basic workings of the brain.

4.1 Neuroscience and Personality

Neuroscience emerged as a discipline in the 1960s and is now a rapidly growing multidisci-plinary science. Neuroscience evolved from anatomy, physiological psychology, medicine, and neuropsychology. One of the earliest and most significant contributors was Donald Hebb, who published his landmark book, The Organization of the Brain: A Neuropsychological Theory, in 1949. Many current neurobiological models of personality are based on this early work, which effectively characterized how the brain learns and how it changes when learning occurs (i.e., “neuroplasticity”), with a focus on the strengthening of neuronal connections. Neuroscience offers new approaches to personality, using recent technological advances that focus on how the brain functions at the neurobiological level. As one of the later arrivals on the scientific landscape, neuroscience strives to understand how the brain, with its biochemical messengers and complex tangle of neurons, gives rise to consciousness and behavior.

Like psychology, it explores the many factors that shape our behavior, but the focus is clearly on the contribution of the nervous system (Weiner & Craighead, 2010). Recent research also sug- gests that neuroscience may shed light on central themes that have arisen in the field of per- sonality, such as the nature of human consciousness and existence, the continuum of emotions that we experience, temperamental variations, our biological response to attachment, and the consequences of other social interactions, as well. For example, evidence now suggests that part of the reason teenagers are sometimes impulsive and thrill-seeking may be related to the fact that their brains are not fully developed until about age 23 (Dobbs, 2011). Because the sheath that surrounds the nerves in teenage brains is not fully developed, their cognitive and emotional processing may be less effective. Thus, while a psychodynamic account might look to the parental relationships to explain impulsivity, neuroscientific models might focus on the brain’s structure or brain chemistry to explain the outcomes.

The human brain is a phenomenal evolutionary development whose complexity is just beginning to be understood in and of itself, let alone in relation to personality. When we consider our own personality and the major factors that have influenced it, it’s easy to conceive of how our social, familial, and other environmental factors may have impacted us. For example, if we experienced abuse of some kind, that may stand out as a salient experience and we may remember how it impacted our character (i.e., either in an adverse manner or in how we adaptively coped). Or

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CHAPTER 4 4.2 An Overview of the Nervous System

perhaps we can easily recall how we seem to mimic a parent’s behavior and approach at handling stress. However, we are less likely to think about the influential factors that were present even before we were born, stamped into our DNA, and sending us on a trajectory that we played no role in choosing. “At the heart of the mind–body debate is the puzzle of how a mass of tissue and the firing of brain cells can possibly produce a mind that is aware of itself and that can experience the color orange, the feeling of pride, and a sense of agency” (Robins, Norem, & Cheek, 1999, p. 456).

Moreover, even though we often think of biological contributions as static, emerging research suggests that even the most fundamental biological processes, such as genes and their expres- sion, are actually responsive to the social environment. This emerging field is called human social genomics (also called “epigenetic” responses; e.g., Slavich & Cole, 2013). Specifically, it appears that some genes are especially responsive to social and environmental regulation (e.g., Idagh- dour et al., 2010). Moreover, it is not the social/environmental events themselves, but rather how the individual subjectively experiences it that appears most important. For example, even though there may be a common social threat, such as alcohol abuse, genetic expression may be influ- enced by the person’s sensitivity to that threat (e.g., O’Donovan, Slavich, Epel, & Neylan, 2013), or their interpretation of the threat (i.e., perceiving it as a threat or challenge; Blascovich, Mendes, Hunter, & Salomon, 1999), or even the perception of social support to deal with a threat (e.g., Eisenberger et al., 2011). In essence, this reflects the merging of personality and neurobiology, as these genetic expressions can become stable individual differences (e.g., Cole et al., 2007), and this also introduces a new conceptualization of genetic-environmental interactions (see Slavich & Cole, 2013, for a review). Thus, all theories of personality, explicitly or otherwise, now recognize the neurobiological foundation of personality, and this perspective is fundamental to personality theory (Corr, 2006).

4.2 An Overview of the Nervous System

In the following sections, we provide a brief review of the nervous system and some of its functions. The Nervous System The human body is regulated and controlled by the nervous system (see Figure 4.1) through a series of positive and negative feedback loops. It is made of up two primary systems: the central nervous system and the peripheral nervous system. The central nervous system (CNS) is com- prised of the brain and the spinal cord. The peripheral nervous system (PNS) is a bundle of nerves whose primary role is to connect the CNS (brain and spinal cord) to the rest of the body.

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CHAPTER 4 4.2 An Overview of the Nervous System

Figure 4.1: The organization of the nervous system

The nervous system is highly interconnected and the understanding of these systems allows for a better understanding of their influence on personality.

The PNS is then divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system has both sensory and motor pathways, with the sensory pathways send- ing input to the brain and spinal cord, while the motor pathways send information from the brain and spinal cord to the muscles and glands. As the name implies, the autonomic nervous system is self-governing, meaning we have little conscious control over its functioning. The autonomic nervous system can then be further divided into the sympathetic nervous system, which controls arousal (e.g., increased heart rate, blood pressure, breathing, dilation of pupils, etc.), and the parasympathetic nervous system, which controls the calming response (e.g., decreased heart rate, blood pressure, breathing, constriction of pupils, etc.).

Neurons—The Building Blocks of the Brain The specialized cells that make up the central nervous system are tiny cells called neurons. Neu- rons are the essential building blocks of the brain, and it is estimated that there are upwards of 100 billion neurons in the human brain and 16 to 23 billion neurons in the cerebral cortex alone, depending on such factors as age and gender (Pakkenberg & Gundersen, 1997; Williams & Herrup, 1988). Their most important function is to communicate information (Squire et al., 2003).

Nervous System

Peripheral Nervous System cranial nerves, spinal nerves

Central Nervous System brain, spinal cord

Somatic Nervous System voluntary

Autonomic Nervous System involuntary

Sympathetic Nervous System

arousal

Parasympathetic Nervous System calming response

skeletal muscles cardiac muscles smooth muscles

glands

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CHAPTER 4 4.2 An Overview of the Nervous System

Figure 4.2: Depiction of a neuron

Each component of the neuron has a specific function in sending and receiving information.

Neurons consist of three major structures (see Figure 4.2): the soma or cell body; dendrites, which are hair-like structures that emanate from the cell body, often with many tree-like branches; and an elongated portion termed the axon. Neurons are connected to other neurons by dendrites and axons. Neural transmission ordinarily proceeds from the cell body outward along the axon and across a space (termed a synapse) to the dendrites of an adjoining/nearby neuron (Carnevale & Hines, 2006).

Neurotransmitters Neurotransmitters are endogenous chemicals (i.e., they are naturally occurring in the human body), and they carry information to other cells across the synaptic gap (see Figure 4.3). The synaptic gap is the space between two neighboring neurons where the neurotransmitters are released when a neuron is activated. Within the synaptic gap, there can be a complex exchange of more than 100 neurotransmitters, including dopamine, monoamine oxidase, serotonin, and acetylcholine, and each neuron can release neurotransmitters (by firing) up to 1,000 times per second.

Dendrite Soma

Axon

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CHAPTER 4 4.2 An Overview of the Nervous System

Figure 4.3: The neurochemical process of neuronal communication

These neighboring neurons are able to share information using a complex process that involves transferring information as an electrical impulse within the sending (presynaptic) neuron and as a chemical message between neurons.

Various neurotransmitters are associated with different emotional and behavioral response ten- dencies and have been implicated in neurological and psychiatric disorders. For example, genetic variability in two neurotransmitters, dopamine and serotonin, can predict risk-taking behavior (Heitland, Oosting, Baas, Massar, Kenemans, & Böcker, 2012), thereby suggesting that certain individuals may require and seek out higher levels of stimulation (Golimbet, Alfimova, Gritsenko, & Ebstein, 2007).

Different types of cells secrete different neurotransmitters; some may be excitatory (lead to neu- ral firing) and others inhibiting (prevent neural firing). Neurotransmitters appear to work in differ- ent areas of the nervous system and have a different effect according to where they are activated. Scientists have identified more than 100 different neurotransmitters, and more continue to be discovered. For a list of some of the neurotransmitters and their primary functions, see Table 4.1. Neurotransmitters play a central role in all human action, and they are also thought to play an integral role in understanding both neurological and psychological disorders, such as Parkinson’s disease and depression.

Synaptic cleftNeurotransmitter

molecule

Postsynaptic membrane

Receptor site

Presynaptic neuron

Presynaptic neuron

Presynaptic membrane

Postsynaptic neuron

Postsynaptic neuron

Neural impulse

Neural impulse

Axon

Axon

Dendrites

Synaptic vesicles

Axon terminal

Neurotransmitter molecule

Postsynaptic membrane

Receptor site

Synaptic cleft

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CHAPTER 4 4.2 An Overview of the Nervous System

What is the rationale for considering clinical constructs such as depression within the context of personality research? Personality traits are closely related to mood states, both conceptually and from a functional standpoint. For example, a mood state is seen as somewhat transient, lasting from several minutes to upwards of several weeks or even months. Personality is thought to be more durable, but there is no clear delineation between how long a state lasts relative to a person- ality trait. Therefore, research focused on understanding the neurobiology of clinical conditions is likewise shedding light on personality functioning.

Table 4.1: Primary neurotransmitters and their functions

Neurotransmitter Function

Dopamine Controls arousal levels in many parts of the brain and is vital for controlling motor activity. When levels are severely depleted, as in Parkinson’s disease, people may find it impossible to control voluntary movements. Overly high levels seem to be implicated in schizophrenia and may give rise to hallucinations.

Serotonin Associated with the regulation of mood, sleep, and appetite. Serotonin has a profound effect on mood and anxiety: High levels of it (or sensitivity to it) are associated with serenity and optimism. Serotonin is also involved in many other physiological functions including sleep, pain, appetite, and blood pressure.

Acetylcholine (ACh) Controls activity in brain areas connected with attention, learning, and memory. People with Alzheimer’s disease typically have low levels of ACh in the cerebral cortex; drugs that boost its action may improve memory in such patients.

Gamma-aminobutyric acid (GABA)

Though technically an amino acid, GABA is often classified as a neurotransmitter. It balances the brain by inhibiting over-excitation (i.e., decreasing the neuron’s action potential), induces relaxation and sleep, controls motor and visual functioning, and is related to symptoms of anxiety.

Noradrenaline Mainly an excitatory chemical that induces physical and mental arousal and heightens mood. Noradrenaline is centrally involved in reactions to stress and panic.

Glutamate As the brain’s major excitatory neurotransmitter, glutamate is vital for forging links between neurons that are the basis of learning and long- term memory.

Enkephalins and endorphins

Endogenous opioids that, like the opiate drugs, modulate pain, reduce stress, and promote a sensation of happiness and well-being. They also depress physical functions like breathing.

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Structural Organization of the Brain The brain is a structure (see Figure 4.4) that looks like a somewhat larger version of your closed fist with your thumb inside. The forward part of your fist with its closed fingers represents the forebrain. Its thin outer shell is the cerebral cortex. The brain divides naturally into two halves, called cerebral hemispheres. The hemispheres are connected by a thick band of fibers called the corpus callosum, which allows for communication between the left and right hemispheres. Your thumb, inside your fist, is the midbrain: it includes the limbic system, which is mainly concerned with emotional processes and memory. It is often referred to as the old mammalian brain because it appeared early in mammal evolution. In this analogy, your wrist is your brain stem (basal gan- glia), which is part of the hindbrain. The hindbrain is sometimes referred to as the reptilian brain because it is thought to be the first evolutionary structure among animal species. This region of the brain is responsible for basic physiological functions, such as breathing and eating. The divi- sions are somewhat of a simplification but are nevertheless instructive (Panksepp, 1998). Follow- ing evolutionary lines, the hindbrain was first to develop; the midbrain was next; and the cerebral cortex covering the brain and accounting for higher mental activities developed last (MacLean, 1990; see also Striedter, 2005, for another perspective).

Figure 4.4: The major structures of the brain

Forebrain

Midbrain

Hindbrain

Spinal cord

The figure depicts the approximate location and relative sizes of the major structures of the brain.

Viewed from the outside, deep crevasses (fissures) divide the cerebral cortex into four regions, termed lobes (see Figure 4.5): the frontal (front of the brain, behind your forehead), parietal (mid section), temporal (bottom section), and occipital (back of brain). Each lobe has primary functions associated with it, but there is also considerable neuroplasticity, meaning that some functional changes can occur with time. Neural plasticity will naturally occur as we develop, but it can be demonstrated in response to brain trauma, where the functions of one part of the brain are taken over by another part of the brain (a phenomenon known as migration of functioning). The latter is more likely to occur, or at least to a greater degree, in the brains of younger individuals; however, recent findings suggest that it can also occur and be enhanced in older adults by having them engage in demanding cognitive tasks (e.g., Delahunt et al., 2009).

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CHAPTER 4 4.2 An Overview of the Nervous System

Each hemisphere of the brain contains four lobes, and each lobe has specific functions. This figure shows the left hemisphere, but the right hemisphere has the same four lobes.

Figure 4.5: The four lobes of the brain

Frontal lobe

Temporal lobe

Parietal lobe

Occipital lobe

The frontal lobe is very important in our ability to plan complex sequences of behavior and engage in rational thinking. The parietal lobe is concerned mainly with sensation relating to touch. The temporal lobe is primarily concerned with language, speech, and hearing. Broca’s area and Wer- nicke’s area are specific parts of the temporal lobe involved in language (Damasio, 1999). Finally, the occipital lobes, located at the very back of the brain, are involved in vision (they contain the visual cortex.).

Another important brain structure, the cerebellum, is located at the back and bottom of the brain. It is a rounded structure that is linked to other regions of the brain by thick bundles of nerve fibers. When functioning normally, it regulates signals involving movements, thoughts, and emotions from other parts of the brain. The cerebellum is arranged in an unusual configuration: It consists of stacks of fanlike, highly compacted neurons.

Specialization of the Brain One of the distinguishing features of the brain is that it is not fully symmetrical in functioning (Gazzaniga, Ivry, & Mangun, 2002; Geschwind, 1979). That is, the two hemispheres of the brain do not share all tasks equally—a phenomenon referred to as lateralization. For example, most individuals have a dominant hemisphere for certain activities. For motor responses, the dominant hemisphere is usually the opposite of your dominant hand. The way the brain is wired, the right side of your body is controlled by your left hemisphere; the left side, by your right hemisphere. For the majority of us—because only about 10% of humans are left handed—the left hemisphere is dominant for motor activities.

Other research on the functions of the hemispheres suggests that the left hemisphere may be more involved than the right in language and logical thinking. The right hemisphere is somewhat more involved in musical aptitude and may be more adept at processing the nonverbal aspects of language, such as recognizing tones. It is also considered the intuitive, emotional, and artistic hemisphere. However, there is enormous overlap in the functions of the two hemispheres.

Broca’s Area

Early in the 20th century, Pierre Broca, a famous brain investigator, noticed that damage to a specific area of the left frontal lobe of the cortex (which is now called Broca’s area) resulted in aphasia—speech disorder. Speech of affected patients was slow and labored, with impaired artic- ulation. He went on to discover that damage to the right frontal lobe left speech intact. What is striking is that patients with what is now labeled Broca’s aphasia can speak only with great dif- ficulty, but they are able to sing with ease (Schlaug, Norton, Marchina, Zipse, & Wan, 2010).

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CHAPTER 4 4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

Wernicke’s Area

Carl Wernicke, another eminent pioneer, studied another area of the cerebral cortex, the tem- poral lobe. Damage in this area of the brain (now called Wernicke’s area) also leads to speech dysfunction, but of a different sort. The speech of patients with Wernicke’s aphasia is grammati- cally normal but demonstrates semantic deviations. The words chosen are often inappropriate or include nonsense syllables (Kolb & Whishaw, 2003).

4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

All aspects of the nervous system interact in important ways, many of which are outside of our control and outside of our awareness. The importance of these interconnections is that their complexity speaks to some of the issues central to the understanding of personal- ity. For example, does personality change due to brain injury? Is the concept of the unconscious informed by autonomic responses that occur outside of our awareness? Can neuroscience provide a new perspective on attachment and separation? We examine these and other questions here.

The Brain and Personality When the brain is injured from trauma (such as a car accident) or organic disease (such as tumors or Alzheimer’s dementia) or from ruptured cerebral blood vessel (stroke), the individual may dem- onstrate dramatic changes in personality. Neuropsychologists can often determine the focal point of a brain injury by the behavioral, social, and emotional consequences (sequelae) of the injury. For example, a patient who suffered from a blow to the head and is unable to talk may have suf- fered damage to Broca’s area of the brain, as mentioned earlier.

There is considerable evidence that damage to various parts of the brain results in different effects on emotional responses. For example, right hemisphere lesions can undermine emotional regula- tion as well as compromising the ability to recognize emotional responses in others (Geschwind, 1979). Lesions in the left side of the brain are often accompanied by depression; in contrast, those with right cerebral damage sometimes seem unconcerned with their condition.

There have been some interesting cases of severe head injuries resulting in altered personality functioning. Of course, there is a limit to the number of cases that we can study because not everyone who experiences a severe head trauma survives, especially in previous centuries. One of the more famous cases in the study of neuroscience was that of Phineas Gage (1823–1860). In a railway accident, a steel rod shot into Gage’s skull and through his frontal cortex. Amazingly, he survived. He was leading a reasonably normal life within four months, but his character had changed dramatically. The local physician who treated Gage described him as impatient and ver- balizing “grossest profanity.” Those who knew him prior to the accident concluded that Gage was “no longer Gage.” The damage to the frontal cortex had significantly reduced his inhibitions, and he routinely engaged in socially inappropriate behavior.

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CHAPTER 4 4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

Recent research has similarly found alterations to the brain produce alterations to personality. One cross- sectional design examined the per- sonality change associated with the neurobiological alterations that occur with early Alzheimer’s demen- tia (Pocnet, Rossier, Antonietti, & von Gunten, 2013). Findings showed decreased openness to new experi- ence (creativity) and conscientious- ness. These findings were consistent with a review of the literature show- ing large and consistent decrease in conscientiousness and openness to new experience (along with reduced agreeableness and increased neu-

roticism) associated with advancing symptoms of Alzheimer’s dementia (Robins Wahlin & Byrne, 2011). Moreover, a similar pattern of personality change also emerged for those with frontotem- poral lobar degeneration (Mahoney, Rohrer, Omar, Rossor, & Warren, 2011).

Dreaming Most of us recall at least some of our dreams—especially those that are lucid (rare dreams where dreamers know they are dreaming) or have strong emotional content. Dreaming is a sign that our brain is at work even while we sleep. Although other theoretical perspectives focus on the dream content and assume that it reveals intrapsychic conflicts, the neurobiological perspective offers an alternate explanatory framework.

The brain can be very active during sleep, with almost as much brain activity during certain aspects of sleep (rapid eye movement sleep, or REM) as is seen during the wake state. Controlled by nuclei in the brainstem, sleep involves a sequence of physiological states. The fact that the brainstem is centrally implicated in controlling dreams is consistent with the belief that dreams occur in all vertebrates. This also highlights the importance of dreaming, as functions that are more widely observed across different species are thought to be more central to survival.

Some research focuses on the mechanism of dream recall rather than the occurrence of the dream. The literature suggests that the neurophysiological mechanisms involved in the encoding and recall of memories (e.g., mediated by hippocampal nuclei), is comparable in both wakefulness and sleep. Moreover, the temporo-parieto-occipital junction and ventromesial prefrontal cortex appear to be especially important to dream recall (De Gennaro, Marzano, Cipolli, & Ferrara, 2012). Research also suggests that brain volume and structure of the hippocampus–amygdala are related to dreaming.

Everett Collection/SuperStock

The entry and exit points of Gage’s skull are depicted here, showing the parts of the brain impacted by the rod.

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CHAPTER 4 4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

The biological explanations for dreams are a far cry from the ideas forwarded by theorists such as Freud and Jung. Neuroscientific explanations distill the dream down to its basic neurochemical reactions and appear to leave little if any room for what we would traditionally refer to as per- sonality. Importantly, although these models provide an important account of the experience of dreaming, the neurobiological evidence does not provide any insight with respect to the dream content (only occurrence). Thus, there may be room at the table for all perspectives when it comes to fully understanding dreams, a domain that has traditionally fallen within the field of personality psychology (see Application Exercise 1 in this chapter for a more detailed consider- ation of this issue).

The Unconscious Neuroscience has made significant contributions to our understanding of the unconscious, and much of the research in this area builds upon the findings reported in Chapter 2 on the cognitive unconscious. Both imaging studies and examinations of the consequences of brain lesions have established that word meaning is processed by the left hemisphere (Damasio, Grabowski, Tranel, Hichwa, & Damasio, 1996). This converges with the material presented earlier in this chapter where we identified the major speech and comprehension centers as being in the left hemisphere.

As noted in Chapter 2, when a study uses briefly presented stimuli and masking, it is possible for stimuli to not be consciously perceived (e.g., Bar & Biederman, 1998). These unconscious stimuli can decrease reaction times (speed up) the subsequent recognition of other conscious stimuli that are semantically related (Dehaene et al., 2001). Neuroscientific research has employed functional magnetic resonance imaging (fMRI) to identify the regions of the brain that respond to the uncon- scious stimuli; the left fusiform gyrus and left precentral gyrus have been implicated (Dehaene et al., 1998, 2001). Electrophysiological studies have likewise identified evoked potentials associated with the influence of masked primes (e.g., Kiefer, 2002). These studies indicate that unconscious processing can be mapped and associated with a specific pattern of responding.

Neurobiological evidence that the brain is able to respond to stimuli without conscious awareness is an important step to validating the existence and role of the unconscious, and its contributions to our personality. Given the controversies associated with the unconscious over the years, such findings are relevant to establishing an explanatory framework that is separate from, or in addi- tion to, that provided by theorists from other perspectives in the field of personality (see Kato & Kanba, 2013; Modell, 2012).

The Fight or Flight Response An important unit of interconnected brain structures of the midbrain and the limbic system is responsible for rapidly responding to danger. This system, termed the hypothalamic-pituitary- adrenal axis (HPA or HTPA axis), includes the hypothalamus, a tiny brain structure, and the pitu- itary and adrenal glands, as well as the limbic system. These are all connected by pathways of neurons in a ring of structures that play a vital role in emotional responding (Sapolsky, 2004). The limbic system is also likely to be a major component of learning complex tasks that require analysis and synthesis. It includes small, almond-like structures called the amygdalae (amygdala in the sin- gular), which are responsible for emotional response in the face of danger. Also part of the limbic system and connected to the amygdala is the hippocampus, which is implicated in memory and is responsible for creating maps of the external world; these are used for rapid pattern recognition.

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CHAPTER 4 4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

One of the essential functions of the limbic system is to regulate the fight-flight response, which was first identified by Walter Cannon (1939; see also Corr, 2006). This response is essential to human adaptation. It is thought to have evolved because of the need for a rapid response system to danger. The advantage of this limbic system structure is that it bypasses the frontal lobes of the brain (responsible for executive functions), providing a direct connection between the brain and muscular systems, thus allowing for immediate reaction when faced with serious danger. It would not be wise to stop and ponder the situation when confronted by a saber tooth tiger, for example; “run first and think later” makes more evolutionary sense. Interestingly, researchers have also indicated that a brief freeze response typically precedes the fight-flight response, during which time the organism is in a heightened state of awareness and their senses engage in information gathering to prepare for the next response (see Adenauer, Catani, Keil, Aichinger, & Neuner, 2009). The addition of the concept of freezing is in keeping with the finding that the first reaction to a threat is usually a decrease in heart rate (Bradley, Codispoti, Cuthbert, & Lang, 2001).

The limbic system is implicated in many stress-related disorders. When there is chronic over- activation of the limbic system, such as might result from continued stress, trauma, or neglect, an organism can experience a state of disequilibrium called allostatic loading (McEwen & Seeman, 2003), a concept that was referred to in Chapter 3. In this state of chronic stress, a number of neurochemical reactions occur, including an increase in the production of stress hormones and steroids. Over time, this can lead to physical and mental disorders, such as PTSD, mood disorders, and anxiety.

Attachment and Separation Although there is very rapid brain growth until age 2, the prefrontal cortex of the brain does not develop fully until adulthood. After age 2, synaptic growth begins to slow, and cells that are not used experience a programmed form of death referred to as neural pruning (Grigsby & Stevens, 2000, p. 290). These findings from neuroscience have important implications for human attach- ment and its influence on our development.

The social world influences the expression of our genes and, through a complex process called epigenesis (see Chapter 3 for a neo-analytic use of this term), may even alter our genes during our lifetime. For example, there is evidence that trauma early in life, resulting from a disruption in attachment through loss, illness, or separation, leads to hormonal and other physiological distur- bances. These changes may alter the trajectory of development (Siegel, 1999).

There is also evidence that there may be sensitive periods for certain kinds of learning. Sensitive periods are times of development when learning is most likely to occur because the indi- vidual is biologically primed for learning a particular behavioral pattern. After—or before—these periods, learning may be more difficult. For example, if you who grew up in a bilingual household, you easily learned two languages. Those who did not learn a second language early in life gener- ally have a much more difficult time doing so later. And in the same way that there appears to be a sensitive period for language learning, there may be sensitive periods for the formation of attachments. Lack of appropriate experiences during these periods may influence our later capac- ity for intimacy with others. Interestingly, similar periods of heightened learning are seen in other species, though the timing for such learning is less flexible, and these are called critical periods.

The literature also suggests that while all stress responses have some common features, specific stress responses may be seen in those with a vulnerability for that particular stressor. For example, research suggests that stress in the form of relationship threats (i.e., separation from an intimate

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CHAPTER 4 4.3 Using Neuroscience to Inform Our Understanding of Human Behavior

partner) can be marked by spikes in cortisol (a steroid hormone, more specifically a glucocorticoid) and these are most evident in men with anxious attachment styles (Powers, Pietromonaco, Gun- licks, & Sayer, 2006). Thus, when the partners of anxiously attached individuals travel, they tend to have higher cortisol levels (Diamond, Hicks, & Otter-Henderson, 2008), presumably because the time away from their partner is more likely to be seen as a threat to the relationship.

As noted in Chapter 3, attachment in other species can be informative to understanding the pro- cess of attachment in humans, especially when dealing with species who have are more neurobio- logically similar. One common aspect to all of the attachment-separation research is that the end result is to create a very focal stress reaction (i.e., stress due to separation). Thus, briefly reviewing the neurobiology of stress is useful.

Stress Response Syndrome and Emotional Trauma Hans Selye borrowed the term stress from the field of engineering and incorporated it within biol- ogy in the 1930s. He used the term to describe a physiological response that is inadequate to an environmental demand (Selye, 1956). Selye suggests that, like the last heavy truck whose added weight destroys the bridge, one more source of psychological stress added to many other stress- ors might have serious and long-lasting consequences.

Seyle’s contribution, in the form of his theory of the General Adaptation Syndrome (GAS), was a major and enduring one. The theory explains that there are three stages in our response to stress (Cooper & Dewe, 2004):

1. alarm, when the flight-fight response is activated (recall that this is the sympathetic nervous system);

2. resistance, when the stressor persists and the body tries to adapt to the strain; and 3. exhaustion, where the body becomes depleted, the immune system impaired, and the

individual is unable to function.

Robert Sapolsky (2004), in his book Why Zebras Don’t Get Ulcers, writes that by ruminating over or re-living a stressful event, humans have the distinct capacity to create a downward cycle in which the effects of glucocorticoids on the human body are debilitating when experienced at high levels or for long periods of time. This contrasts with other species, such as a zebra, which after escaping (or before being chased by) a predator, appears not to be especially concerned and is not marked by the ruminative worry commonly displayed in humans.

The effects of stress on both physiological and psychological functions have been well documented. Chronic stress can result in a disturbance to our immune system as well as a disruption of per- sonality functioning. As Kramer (1993) explains, “Pain, isolation, confinement, and lack of control can lead to structural changes in the brain and can kindle progressively more autonomous acute symptoms” (p. 117). For example, psychological stress causes reductions in certain hormones such as beta-endorphin, glucocorticoid, and prolactin. Also, the effects of sexual abuse produce consis- tently higher levels of cortisol and more easily triggered cortisol responses to stimulation, which have been linked to higher levels of depression and post-traumatic stress disorder.

Emotional trauma is another way of conceptualizing stress. Trauma is a severe emotional response to an overwhelming event, such as rape, assault, natural disasters, torture, and psychological abuse. Symptoms can include flashbacks, relational disturbances, somatic (bodily) complaints, and unpredictable emotions. More subtle forms of what is termed relational trauma early in

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CHAPTER 4 4.4 Temperamental Substrate of Personality

life—for example, neglect and caregiver abuse—can adversely affect limbic system development (Schore, 2003).

High emotional arousal associated with traumatic experience has been found to be a consistent element of many severe personality disorders as well as of major depression (Levitan et al., 1998). Conversely, too little emotional activation can also have a profound effect on various aspects of personality. The National Institute of Mental Health’s (1995) report summarizing experimental and clinical studies on post-traumatic stress disorder describes the impact on a variety of neural systems, but especially the limbic system of the brain. It is clear from the accruing evidence that trauma can have a permanent impact on the attachment system and can lead to later personality disorders and psychological disturbances (Beebe & Lachmann, 2002).

Neuroscientists have found evidence that the limbic system is part of a complex of interconnected brain regions related to emotion (Sapolsky, 2004). When animals and humans experience acute stress, they can often recover with time. But in certain situations, acute or chronic low-level stress can sensitize the limbic system, activating the stress-response circuits in the brain. Harlow showed that among infant monkeys, stress from attachment disruption is a factor in later psychopathol- ogy. And developmental psychologists have shown that disrupting attachment even briefly leads to profound changes in the infant’s attachment system.

Personality development is influenced by a number of factors, including genetic predisposition and neonatal development, but emotionally traumatic events can kindle certain neuronal path- ways that then become sensitized and overact in given situations. In this context, kindling refers to the repeated stimulation of brain circuits, which can induce epilepsy and personality changes (Panksepp, 1998). Thus, kindling may lead to actual changes in limbic structures.

It seems clear that stress interacts with our neurobiology and impacts our personality and our development.

4.4 Temperamental Substrate of Personality

Temperament is a largely biological—hence inherited—dimension that can also be influenced by maternal health and neonatal factors, such as maternal substance abuse, depression, ill-ness, and malnutrition. Temperament is the substrate of personality that provides us with the genetic encoding that shapes much of our personality.

Temperament influences our personality development by providing the parameters that our envi- ronment will shape into our unique self. As an analogue, height is largely genetically determined. But the nutrition, or the malnutrition, provided by the environment is what determines your final height—in addition to the possibility of growth-stunting illness, disease, or glandular malfunction, which could conceivably make you much shorter or taller than expected. Temperament, too, is influenced by a plethora of biological and prenatal factors, such as genetic predisposition, and prenatal influences, including maternal health, smoking, environmental toxins, and nutrition. Stress hormones and neurotransmitters have a substantial impact on temperamental variation. The study and classification of temperamental variation represents a major advance in develop- mental psychology with important implications for neurobiological models of personality. There have been many theoretical models forwarded, but we will here present one of the more influen- tial of these.

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CHAPTER 4 4.4 Temperamental Substrate of Personality

Thomas and Chess (1977) were early innovators in the study of temperament, suggesting that it has a pervasive influence on our personality development and that any comprehensive model of personality must account for this influence. Thomas and Chess’s classification system is especially useful in this regard.

Thomas and Chess’s Classification of Temperament Thomas and Chess (Chess & Thomas, 1986; Thomas & Chess, 1977; Thomas, Chess, & Birch, 1968) did important work observing and systematically rating several hundred infants from birth to early adolescence. They identified nine categories of temperament (Thomas & Chess, 1977, pp. 21–22):

• Activity level. This is the child’s level of motor activity reflected in the proportion of active and inactive periods during a typical day.

• Rhythmicity (regularity). This refers to the predictability of the child’s behaviors. • Approach or withdrawal. This dimension of temperament is evident in the nature of the

infant’s initial response to a new stimulus such as a new food, different toy, or strange person.

• Adaptability. This is reflected in responses to new or changed situations. • Threshold of responsiveness. This is indicated by the intensity of stimulation required to

evoke a visual, auditory, or tactile response. • Intensity of reaction. This is the energy level of response, regardless of its quality or

direction. • Quality of mood. Mood is reflected in pleasant, joyful, and friendly behavior or in

unpleasant, crying, and unfriendly behavior. • Distractibility. The effectiveness of extraneous environmental stimuli in interfering with

or in altering the direction of the ongoing behavior. • Attention span and persistence.

Attention span is defined by the length of time during which the child engages in a particular activity. Persistence refers to the continuation of an activity in the face of obstacles.

In their studies, Thomas and Chess observed that infants demonstrated rec- ognizable patterns even in the first few months. This was a critical finding that supported what most parents realize: Children are not born the same, and this can be explained by genetic variations. Some children have very demanding, dif- ficult temperaments from birth, whereas others are easily calmed and responsive to maternal input.

Based on their findings, Thomas and Chess were able to reduce their nine factors to two central dimensions of temperament: activity pattern and adaptability. Activity refers to whether a child is vigorous and continuously interactive with the environment or tends to be passive. Adaptability refers to a child’s positive approach to new stimuli in the environment. Some children tend to

Pojoslaw/iStock/Thinkstock

How much of personality is due to natural temperament versus what we learn from caregivers and the environment?

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CHAPTER 4

approach new stimuli with a high degree of flexibility and are able to respond to the changing demands of their environment; others tend to withdraw, often expressing negative moods when exposed to novel situations.

There are three major temperamental variations, explain Thomas and Chess: the easy child, the difficult child, and the slow-to-warm child. Jerome Kagan added two categories to Thomas and Chess’s descriptions: He identified infants who were distressed and inactive but cried a lot and others who were aroused and highly active but did not cry. He found that these temperamen- tal variations often predicted later difficulties such as anxiety and conduct disorder—a finding that supports the belief that infant temperament influences adult personality (Kagan & Snidman, 2004). Interestingly, such temperamental differences have also been documented in other spe- cies, such as “shy” rhesus monkeys (Suomi, 2009). Suomi notes that these behaviors and the pre- sumed biological causes are stable into adulthood and can be passed on to the next generation, but they can also be modified by environmental factors.

Thus, it appears that even complex interpersonal processes such as attachment and separation (discussed in Chapter 3), which are thought to be central in the early formation of personality (i.e., temperament) can be represented in neurobiological terms. However, simply representing personality constructs is not sufficient to justify the discussion of neurobiology in the field of per- sonality. Instead, it is necessary to also consider theoretical models that explicitly link personality to neuroscience, and that is the focus of the next section.

4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

Personality neuroscience is the branch of neurological sciences that investigates how pro-cesses in the brain influence interaction between environment and genes (DeYoung & Gray, 2009). Neurobiological models represent neuroscience’s initial attempts to develop neuro- biologically based models of personality showing how brain processes, and especially the activity of neurotransmitters, are linked to personality traits and variations in personality (DeYoung & Gray, 2009).

We will here review five important neurobiological models: (1) Eysenck’s three-factor model, (2) Buss and Plomin’s three-factor temperament model, (3) Depue’s three-factor model, (4) Clon- inger’s unified biosocial theory of personality, and (5) Siever’s dimensional model.

Eysenck’s Three-Factor Model Eysenck believed that differences in personality that could be observed around the world were due to biological variability. Eysenck stated that there were stable variations in biology that could predict important outcomes. He proposed three basic factors: (1) introversion/extraversion, (2) neuroticism/emotional stability, and (3) psychoticism/ego strength. Eysenck stated that the first two factors were relevant to the nonclinical population, whereas all three factors were relevant when considering variation in clinical populations.

1. Extraversion/Introversion. Eysenck linked this factor to activity in the ascending reticular activating system (ARAS). We will elaborate on this specific factor below because it garnered the most research support.

4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

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2. Neuroticism/Emotional Stability. Emotional stability/instability was thought to be a very basic emotional experience and was theoretically linked to activity in the amygdala.

3. Psychoticism/Ego Strength. For those in the nonclinical population, there was thought to be minimal variability on this factor, with virtually everyone exhibiting high ego strength.

As noted, the area receiving the most attention was the model linking activity in the ARAS to the trait of extraversion/introversion. Eysenck (1967; Strelau & Eysenck, 1987) worked on the assumption that the ARAS regulated the flow of information and stimulation to the brain, with some people allowing a great deal of stimulation to the brain, while others allow very little stimu- lation to the brain. Specifically, the former group was referred to as introverts, who were thought to have relatively weak inhibitory and strong excitatory tendencies, resulting in a high degree of cortical arousal. In contrast, extraverts were thought to have relatively strong inhibitory and weak excitatory tendencies, resulting in lower levels of cortical arousal. For this reason, Eysenck believed that extraverts were generally understimulated and therefore had to engage in behavior to achieve brain stimulation (e.g., a high number of social interactions and gravitating to other high-stimulus experiences). In contrast, Eysenck suggested that introverts are typically overstimu- lated and would therefore engage in behavior to minimize brain stimulation (e.g., avoiding social interactions and other forms of stimulation).

Although this theoretical model garnered much attention, the research did not fully support the theory as stated. It turns out that introverts and extraverts do not necessarily differ in how much stimulation enters the brain in general. Thus, in the absence of stimulation, there would not be any differences between the stimulation experienced by the brains of introverts and extraverts. However, research suggests that they do differ in their response to stimulation. Thus, the litera- ture provides at least partial support for the revised model (Bakan & Leckart, 1966; Bartol, 1975; Farley & Farley, 1967; Phillip & Wilde, 1970). Eysenck also hypothesized that depressant drugs elevate cortical inhibition, lower cortical excitation, and result in what is commonly characterized as extraverted behavior (Eysenck, 1960b). In general, these findings converge with more recent lines of research redefining extraversion as “sensation seekers” (Zuckerman, 1998) or focusing on other parts of the brain (i.e., not limiting themselves to the ARAS; e.g., Gray et al., 2005).

It should be noted that the models that follow have many of the same assumptions as Eysenck’s model, but they benefitted from more contemporary research and technology.

Buss and Plomin’s Model Buss and Plomin’s (1975, 1984) three-factor temperament model is designed to explain variations in personality. They believed that traits are largely inherited and are grounded in neurobiology. The three factors that define their model and are reflected in personality are (1) activity, (2) emo- tionality, and (3) sociability:

1. Activity. This factor is defined as the extent to which an individual tends to be tireless and constantly moving or lethargic and passive.

2. Emotionality. This factor is evident in the tendency to become easily emotionally aroused (displaying temper, mood swings, and high expressiveness) or slow to emotional arousal (calm, nonreactive).

3. Sociability. This factor is apparent in the need to be with others (finding social interac- tion gratifying) or appearing detached and uninterested in social discourse.

4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

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CHAPTER 4 4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

Various combinations of these factors account for different personality configurations. For exam- ple, an introvert is low on sociability and activity, but an extrovert is at the opposite pole on both (Millon & Davis, 1996b). An individual with a hysterical personality is high in sociability, emotion- ality, and activity; a depressive personality is low in sociability, emotionality, and activity. Each personality represents a unique combination of these three factors. Buss and Plomin’s research expands upon the work attempting to tie these factors into underlying neurobiological systems (Zentner & Bates, 2008). More recently, researchers have attempted to summarize, compare, and synthesize some the dominant models of personality and link them to child temperament (e.g., Zentner & Bates, 2008).

Depue’s Three-Factor Model Depue’s (1996) work presents a more direct attempt to link factors to the activity of neurotrans- mitters. Depue (1996) accounts for personality in terms of underlying neurobiological systems that he associates with three “superfactors” that have consistently been reported in the research to explain personality: (1) positive emotionality, (2) constraint, and (3) negative emotionality.

Positive Emotionality

Depue (1996; see also Depue & Collins, 1999) proposes that one of the major factors under- lying personality structure is positive emotionality. This is the ability to “experience feelings of incentive, effectance motivation, excitement, ambition, potency, positive affect, and well-being” (pp. 353–354). He describes three core processes involved: “(1) incentive-reward motivation, (2) forward locomotion as a means of supporting goal acquisition, and (3) cognitive processes” (p. 354). Being positive, suggests Depue, is closely related to dopaminergic systems (DA) within the brain. We know that the neurotransmitter dopamine is closely associated with reinforcement, and therefore with feelings of well-being (hence with positive emotions). Positive emotions clearly have a strong influence on our reactions and our personalities, and recent research provides some support for this theory, as it differentiates incentive-reward motivation (also referred to as extra- version) in terms of reactions to positive affective priming (e.g., Robinson, Moeller, & Ode, 2010).

Constraint

The second superfactor in this three-factor model is constraint, a factor sometimes referred to as (low) psychoticism or (high) ego strength. In a literal sense, a constraint is a restriction or a limitation. Hence, constraint is closely related to impulse control, the desire to avoid harm, and uneasiness when faced with new situations. The neurobiological correlate of impulsivity, explains Depue, appears to be the neurotransmitter serotonin (5-HT). In support of this contention, Brown, Goodwin, Ballenger, Goyer, and Mason (1979) found that men who were characteristically explo- sive and impulsive and had an aggressive life history were likely to have a low level of a major metabolite of 5-HT in their cerebrospinal fluid (CSF). Those with higher levels, it is suspected, need much more stimulation to react aggressively (e.g., Depue, 1996).

Related to this, low 5-HT is associated with violent suicidal behavior. Depue proposes that aggres- sion and suicidal behavior are two possible outcomes of a biochemical/behavioral trait evident in a low emotional threshold. In his review of both the animal behavior research and human studies, he proposes three characteristics of low 5-HT functioning: (1) emotional instability, (2) exagger- ated response to stimuli, and (3) irritability-hypersensitivity.

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CHAPTER 4 4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

Negative Emotionality

The third superfactor, negative emotionality, is often apparent in various negative emotions such as depression, hostility, anxiety, alienation, and sensitivity to distress. Depue (1996) hypothesizes that negative emotionality may be linked with the neurotransmitter norepinephrine (NE), as well as a number of other neurotransmitters.

In spite of the apparently close connection between neurotransmitters, emotions, and person- ality, Depue cautions that theories of personality based on suspected neurotransmitter actions are overly simplistic, as a complete explanation of personality requires the inclusion of many other factors.

Cloninger’s Unified Biosocial Theory of Personality Cloninger’s (1986a, 1986b) trait-based neurobiological model of personality proposes that there are three main characteristics, which are heritable: (1) novelty seeking, (2) harm avoidance, and (3) reward dependence. These characteristics, or personality dispositions, are associated with three neurotransmitter systems:

1. Novelty seeking. Novelty-seeking individuals actively pursue novel situations because of the excitement and feeling of exhilaration that these activities produce. This behavioral trait is related to the dopamine (DA) system. Individuals with high levels of dopamine are more likely to demonstrate this trait. Individuals with lower levels of this neurotransmit- ter are likely to be less active, more passive, and preoccupied with details.

2. Harm avoidance. Harm-avoidant individuals respond strongly to aversive stimuli and will therefore do what they can to minimize behaviors that might result in pain or other negative outcomes. This behavioral trait is associated with serotonin (the 5-HT system). Individuals with this trait are more likely to be inhibited.

3. Reward dependence. Reward dependence is the tendency to respond to stimuli that suggest a reward is forthcoming. This trait is associated with the noradrenergic system.

In Cloninger’s biosocial theory of personality, these three neurobehavioral predispositions— reward dependence, harm avoidance, and novelty seeking—set the parameters for the develop- ment of personality (Kramer, 1993). Various personality types are likely associated with these dif- ferent predispositions. Each system is hypothesized to be independent so that an individual might be high on one dimension but low on the others—or high on all three. For example, someone with a histrionic personality is likely high in novelty seeking and reward dependence but low in harm avoidance (Millon & Davis, 1996b).

Although it has some intuitive appeal, recent research has uncovered problems with Cloninger’s model. Specifically, Cloninger’s research has not replicated well, and the validity of the factors remains in doubt. In addition, there is evidence against the belief that single neurotransmitter systems are associated with these traits.

Siever’s Dimensional Model Siever’s (Siever & Davis, 1991; Siever, Klar, & Coccaro, 1985) neurobiological model of personality is termed dimensional because it proposes that personality predispositions exist on a continuum, as though ordered on a dimension ranging from one extreme to its opposite. Maladaptive person- ality represents one end of the dimension; at the opposite end is normal personality.

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CHAPTER 4 4.5 Personality Neuroscience: An Overview of the Theoretical Neurobiological Models

Siever proposes four neurobiological predispositions: (1) cognitive/perceptual organization, (2) impulsivity/aggression, (3) affective instability, and (4) anxiety/inhibition. For each of these neurobiological predispositions, inadequate or faulty neurobiological systems will be evident in different disorders and maladaptations:

1. Cognitive/perceptual organization. Individuals with inadequate neurobiological systems are likely to display schizophrenic disorders and other psychotic symptoms.

2. Impulsivity/aggression. On this dimension, individuals with faulty neurobiological systems will manifest poor impulse control and aggressive acting-out. These individuals will tend toward borderline and antisocial personality disorders.

3. Affective instability. Here, inadequate neurobiological systems may be apparent in emotional instability and inability to control emotions. This can become an obstacle to stable interpersonal relationships. Such individuals may develop borderline or histrionic personalities.

4. Anxiety/inhibition. Faulty neurobiological systems may be apparent in extreme anxiety that, if left unchecked, may develop into disorders such as avoidant and compulsive per- sonality disorder.

Each of the above-described models offers different theoretical organizations and an attempt to account for the broadest range of human behavior and to link findings to some of the dominant trait models of personality, such as the Big Five (e.g., Dyson, Olino, Durbin, Goldsmith, & Klein, 2012; the Big Five and other related models will be discussed in greater detail in Chapter 8). One of the challenges of this work is to account for all manifestations of personality, even though not all personality factors may be grounded in neurobiology (or at least not to the same degree). Although different theoretical perspectives have been offered, including some interesting unifying frameworks linking personality to neural networks (e.g., Read et al., 2010), it is the application of these theories that ultimately determines their acceptance.

Application of Neurobiological Models There are a number of ways that neurobiological models are being used to advance science and practice. For example, researchers studying early stimulation on infants (either excess or depriva- tion) suggest that there can be considerable long-term consequences. As an illustration, if certain neurotransmitters and neuronal pathways are not stimulated during important developmental periods, damage may result to the neurobiological substrate, leading to a range of possible nega- tive outcomes (Millon & Davis, 1996b). Furthermore, early intense levels of stimulation, such as those seen in trauma, may result in changes in neurophysiology and brain weight, with measur- able structural differences in some areas.

Probably the most notable application of neurobiological models has been in the field of psychia- try that, which for the most part, has left behind psychosocial treatments for mental disorders and has become increasingly biological in its assumptions and methods. Drugs are now the treatment of choice for most mental disorders (called pharmacotherapy). As a result of the widespread use of pharmacotherapy, some are questioning the benefit of such interventions, even suggesting that they may have created an epidemic of mental illness (Whitaker, 2010). Pharmacotherapy is used fairly extensively in the treatment of individuals with personality disorders, in spite of the fact that there is little research supporting its effectiveness. Some psychiatrists even use drugs to treat problems such as chronic shyness or rejection sensitivity; this is known as cosmetic psychophar- macology and it remains controversial.

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CHAPTER 4 4.6 Studying the Genetic Basis of Human Behavior and Personality

Other applications of neurobiological models include using EEG (brain wave) mapping to try to dis- cern personality patterns of individuals. Brain imaging is also being used to better understand the neurobiological correlates of various personality disorders, such as the psychopathic and border- line. Recordings of brain activity are also used in an attempt to determine a person’s truthfulness.

4.6 Studying the Genetic Basis of Human Behavior and Personality

The basis of heredity remained a mystery until the Nobel Prize winners J. D. Watson and Crick (1953) discovered the structure of DNA. Another major breakthrough occurred when sci-entists succeeded in reading and mapping the entire human genome—a map that contains approximately three billion characters of text found in DNA molecules (Ridley, 2000). The genome is the basis of heritability.

The way in which genes are expressed—that is, our apparent characteristics—is our phenotype; genotype refers to underlying genetic material. It is clear that genetic predisposition (genotype) sets the stage for personality development and makes a considerable contribution to individual differences (to phenotype; Plomin, DeFries, McClean, & McGuffin, 2001). But trying to sort out the relative contribution of genes and the environment is not a simple task. It is made much easier when researchers have access to a pool of individuals with identical or similar genetics, and with similar or very different environments. That pool is provided by a naturally occurring phenom- enon: that of twins, most of whom are reared in very similar environments, but some of whom are separated at birth and sometimes brought up in dramatically different circumstances. In compar- ing twins reared together and twins reared apart, it is possible to determine the extent to which genes can explain human behavior.

Heritability is the term that refers to the relative contribution of our genes or heredity. Studies of twins have been the standard approach for determining heritability of various factors including personality. More specifically, heritability is a statistical calculation describing the effect size of our genes and proportion of observed (phenotypic) variation that can be attributed to our genes (Plo- min & Caspi, 1999, p. 252). Twin studies have consistently suggested that genetic contribution (or heritability) can account for 50% of the variance in personality. Note, however, that this does not mean that genes determine 50% of our personality, and environment accounts for the other 50%. Measures of heritability refer to variance (variation) and not to absolute amount. So our genes might explain approximately 50% of the variation (differences) in traits such as aggressiveness or impulsivity when we are compared with others, but they do not account for half of our impulsivity or aggressiveness.

Still, explaining 50% of the variance in personality is a significant achievement, since behavior is determined by many factors. Most research in this area finds few factors that account for more than 10% of the variance for any given trait. These findings have been supported by many stud- ies comparing monozygotic (MZ) (i.e., identical twins who share 100% genetic make-up), and dizygotic (DZ) twins (fraternal twins who share 50% genetic make-up), and full siblings (who also share 50% genetic make-up). Since identical twins share the same genetic complement, compar- ing them with non-identical twins, siblings, and unrelated individuals is a highly informative way of examining the interaction of heredity and environment.

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Studies of twins reveal that the personalities of identical twins are significantly more similar than those of fraternal twins—and this seems to be the case for a variety of personality characteristics, including extroversion and introversion. Plomin and Caspi (1999) report, “Across dozens of self- report personality questionnaires, twin correlations are consistently greater for identical twins than for fraternal twins for other traits in addition to Extraversion and Neuroticism” (p. 252). Cit- ing a study by Loehlin (1992), the authors write that three of the big five factors (more on these factors in Chapter 8), measuring agreeableness, conscientiousness, and openness to new experi- ence, have heritability coefficients of approximately 0.40. However, the highest heritability coef- ficients are seen with neuroticism and extraversion, with these big five factors having heritability coefficients of approximately 0.60. Thus, when considering the role of genetics in personality, it appears that the findings vary depending on the specific trait or factor under consideration.

Twin studies have become the standard of practice in research attempting to generate heritabil- ity coefficients, as they provide a reasonably effective methodology for separating the effects of genetics from that of environment. As a result of this research, scientists have concluded that shared genetics are much more important than shared environments in predicting the personality overlap among family members (Plomin & Caspi, 1999). Shared environmental factors can refer to loss, social class, and parenting style, to name a few, which are assumed to be relatively common for all children in a family. Research on twins has determined that parental loss, for example, is a shared factor that makes children from the same family similar, because there is an increased likelihood of anxiety and depression as a result of parental death and divorce.

Considering the Chorionic Status of Monozygotic Twins As noted, twin studies are the workhorse methodology for assessing the role of genetic and envi- ronmental contributors to personality functioning. However, traditional twin research appears to be based on the as-yet-unproven assumption that MZ and DZ twins experience identical (or at least similar) prenatal conditions. Despite the tentative nature of this conclusion, this has not prevented researchers from making overly definitive conclusions regarding genetic hypotheses, even in professional journals (e.g., Rose, 1995). In order to address this shortcoming, research- ers (Phelps, Davis, & Schartz, 1997) have suggested the use of chorion (a membrane that exists between the fetus and mother) control studies to examine prenatal influences, by comparing monozygotic (MZ) twins who shared a single placenta and chorion with MZ twins who came from separate chorion and placenta. Importantly, anywhere from 66% to 75% of MZ twins come from a single placenta and chorion, and these are labeled monochorionic MZ twins. Approximately 25% to 33% of MZ twins are dichorionic; coming from two placenta and two chorions (see Figure 4.6). In contrast, virtually all dizygotic twins come from two placenta and chorions. These two groups allow for the exploration of environmental factors by looking at the discordance between MZ twins.

4.6 Studying the Genetic Basis of Human Behavior and Personality

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CHAPTER 4 4.6 Studying the Genetic Basis of Human Behavior and Personality

Figure 4.6: Dichorionic and monochorionic twins

According to Phelps and colleagues (Phelps et al., 1997), such chorion control studies have revealed greater dissimilarities in dichorionic MZ twins relative to monochorionic MZ twins with respect to birth weights and medical conditions. However, greater similarities were observed in personality variables. For example, in comparing monochorionic MZ twins to dichorionic MZ twins aged 4–6 years, the monochorionic twins were more similar than dichorionic twins on all person- ality measures, despite the fact that there were no differences between the groups on measures of cognitive functioning (Sokol et al., 1995). Importantly, these observed differences could not be due to genetics, as all twin pairs share 100% of their genetic make-up. Thus, it is possible that the pre-birth environment may be especially important to influencing personality, and it is possible that different pre-birth environments (i.e., in one placenta vs. in neighboring placenta) may even trigger different genetic expressions. When these findings are interpreted in this manner, they are consistent with current theories on human social genomics discussed earlier in this chapter (e.g., Slavich & Cole, 2013).

Interestingly, the differences emerging at ages 4–6 may not be present earlier in life, as a study comparing temperament found no differences between monochorionic and dichorionic MZ twins on such dimensions as irritability, activity level while asleep and awake, and reactivity (Riese, 1999). Obviously, given the age of the children tested, these temperament assessments were completed using observational data. When these findings are compared to earlier findings, it sug- gests that any emergent differences may need environmental involvement before manifesting.

Dr. Najeeb Layyous/Science Source/Photo Researchers

These images taken from a colored 3-D ultrasound scan of twin fetuses depict two chorionic arrangements, with the image on the left depicting the arrangement for most dizygotic and some monozygotic twins (i.e., dichorionic), and the image on the right depicting the arrangement for most monozygotic twins (i.e., monochorionic). Notice how one twin in the dichorionic arrangement appears smaller.

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Molecular Genetics and Personality Molecular genetics, which is the study of heredity at the level of genetic structure, has within the last two decades focused on identifying the specific genes that might be responsible for certain personality characteristics (Plomin & Caspi, 1999). Unfortunately, the search for specific genes is challenging. Research now indicates that a single gene is unlikely to account for a specific person- ality attribute. The heritability of personality traits is much more likely to involve the interaction of many genes, each with small variations in effect size. This means that detecting those genes is a difficult undertaking.

The multiple genes that shape complex traits are referred to as quantitative trait loci (QTLs). Plo- min and Caspi (1999) believe that the goal of this line of research is to find the combinations of genes that contribute various effect sizes to the variance of personality traits. Of course, finding the genes that predict a small amount of variance in personality traits will be especially difficult. For this reason, the genes that contribute minimally to trait heritability may never be identified (Plomin & Caspi, 1999; Visscher, Hill, & Wray, 2008).

New findings in molecular genetics also suggest that that some DNA sequences can change their position within the genome of mammals and appear to play a critical role in human develop- ment (e.g. Cowley & Oakey, 2013). These are now referred to as transposable elements, but were previously referred to as jumping genes when they were first identified over a half century ago (McClintock, 1950).

Converging Branches of Neuroscience Neuroscience has led to many new developments in related disciplines, many of which deepen our understanding of the neurobiological basis of behavior, learning, consciousness, and person- ality (Damasio, 1999). There is much overlap among these somewhat different new disciplines of neuroscience. All share similar tools and methods (these will be presented in detail in the last section of this chapter), and all deal with neurological and/or biological systems. The major differ- ences among them often relate to how they emerged from different areas of behavioral science. Among areas of study most relevant to the study of personality are cognitive neuroscience, affec- tive neuroscience, and interpersonal neuroscience.

Cognitive Neuroscience

Cognitive neuroscience is concerned with brain-based theories of cognitive development (Gaz- zaniga, Ivry, & Mangun, 1998). Blending neuroscience and cognitive science, researchers in this field investigate the neurobiological basis of learning (Gazzaniga, 1991). Some cognitive neuro- scientists also focus on the area of artificial intelligence, which is part of the field of computer sci- ence. Computer scientists and neuroscientists are attempting to build intelligent machines using computer modeling. More recently, cognitive neuroscience has been focusing on the importance of affect and the inseparability of cognitive and affective processes (Lane & Nadel, 2000). Find- ings from cognitive neuroscience shed light on the basic cognitive and perceptual processes that shape our personality.

The Human Brain Project is probably one of the most ambitious undertakings of cognitive neu- roscience, similar in scope in many ways to the Human Genome Project (an undertaking that suc- ceeded in mapping the entire human genetic structure). Headed by Henry Markum and based in

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Switzerland, the Human Brain Project is building software that uses basic biological rules to make a three-dimensional computer model designed to simulate activity of the human brain. So far, the Human Brain Project has built a massive computer called Blue Gene. It consists of four computers, each the size of a refrigerator, with more than 16,000 processors designed to simulate the action of neurons. Researchers hope that at some point this project may even be able to replicate con- sciousness (Kushner, 2011).

Affective Neuroscience

Another rapidly growing branch of neuroscience, which is shedding light on the emotional pro- cesses of personality, is affective neuroscience (Davidson, Scherer, & Goldsmith, 2003). The study of emotion (or affect) was not considered worthy of scientific inquiry until the later half of the 20th century.

Important books began to appear, such as The Nature of Emotion: Fundamental Questions by Paul Ekman and Richard Davidson (1994), early pioneers in the study of emotion. Ekman later went on to study the facial expression of emotion by carefully cataloguing the various macro- and micro- expressions of possible emotions using the 43 facial muscles, referred to as action units (Ekman & Rosenberg, 2005). The power of our emotional expressions is evidenced by the research showing that the physical act of smiling may, by itself, induce happiness, resulting in the exploration of the therapeutic benefits of smiling (Abel & Hester, 2002). It also appears that not all smiles are the same. Smiles that involve all of the muscles around the mouth and eyes, referred to as the Duch- enne smile (named after the physician Guillaume Duchenne, who studied the physiology of smil- ing) typically evidence the strongest association with self-rated happiness (e.g., Scherer & Ceschi, 2000). One interesting line of recent research focuses on the extent to which individuals can con- trol the physiological manifestations of a smile, even a Duchenne smile. Despite earlier beliefs to the contrary, more recent studies suggest that we can control such facial responses (Gunnery, Hall, & Ruben, 2012), and on a related theme, researchers are currently exploring the way in which we regulate our emotions, which is very important in trying to understand normal as well as patho- logical personality adaptations.

Stanley Greenspan (1997) believed that there is considerable evidence to suggest that emotions play a critical part in the creation and organization of the mind’s most crucial structures. For example, when an individual is the victim of early trauma, the level of emotional arousal may overwhelm the developing mind and alter the developmental structure of the brain. Greenspan also argues that everything from intellect to morality has its origins in the earliest emotional experiences and continues to influence us throughout our lives. For example, there is neurobiological evidence to sug- gest that physical touching stimulates hormones such as oxytocin, which fos- ters positive feelings of closeness and attachment.

Benjamin A. Peterson/Mother Image/mother image/Fuse/Thinkstock

Research suggests that physical contact can stimulate hormones to foster positive feelings that co-occur with physical closeness. This may demonstrate a neurobiological model for attachment.

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Affective neuroscientists are beginning to understand the influence of stress on our neurobiologi- cal system. One fruitful area of investigation is the effect of stress on our neuroendocrine system, which produces hormones, which in turn have a strong influence on our behavior. Testosterone, for example, is related to aggression, and other hormones such as adrenalin and cortisol prime us for action (Sapolsky, 2004). Elevated levels of stress hormones can have damaging effects on the hippocampus and amygdala, which are the emotional and memory centers of our brain. In fact, it may be that these hormones interfere with neurogenesis—the growth of new neurons—resulting in smaller hippocampal size (and medial prefrontal cortex) in individuals suffering from PTSD (e.g., Herringa, Phillips, Almeida, Insana, & Germain, 2012).

Interpersonal Neuroscience

Another fairly recent new discipline is interpersonal neuroscience. Related to affective neurosci- ence, but placing its emphasis squarely on the primacy of interpersonal experience, this branch of neuroscience has been popularized by the work of Daniel Siegel. He believes that our relationships have a powerful effect on our brain circuitry because the regions of the brain responsible for social perception and interpersonal communication are also critical for regulating body states, mem- ory, and emotional processes (Siegel, 1999, 2006). Siegel draws heavily on attachment theory to ground his neurobiologically based interpersonal model.

Of course, Siegal was not the first to make this connection. Well over a century ago, William James (1890) pointed out that intense emotional experiences may scar cerebral tissue and create last- ing changes in neural activity. Thus, the quality of attachments in childhood may have a profound effect on personality in adulthood by how they affect the physical structure of the brain. Insecure attachment may create an increased risk for psychological and social impairment.

There are some relatively new branches of neuroscience that are related to the mind-body con- nection and are thus salient to the study of personality. In Chapter 1 we briefly looked at the emerging field of epigenetics. Here we will examine that field in greater detail. We will also look at the emerging science around our understanding of the complex interactions of neuropeptides and their opiate receptors, which also have a strong relation to our moods and emotions.

Emerging Branches of Neuroscience: Epigenetics As noted earlier in this chapter, the discovery in 1953 by Watson and Crick of the structure of DNA led to the mapping of the human genome in 2000. This discovery was believed to provide us with a blueprint for all humans. Indeed, it has led to many advances for treating diseases and allowed us to study heritability in ways that were not possible before. But DNA is not completely precise, and the genome could not explain why two people with identical DNA could, in some cases, be quite different from each other. According to Carey (2012), DNA is less like a factory mold and more like a script. Factory molds will produce the exact same product over and over again. How- ever, the same script can tell very different versions of the same story depending on the directors, the actors, and the elements of production.

Scientists have been studying this phenomenon for years. It is not the focus of this text to delve into the molecular details of the science, but Carey (2012) provides a concise explanation that suits our purposes:

The DNA in our cells is not some pure unadulterated molecule. Small chemical groups can be added at specific regions of DNA. Our DNA is also smothered in special proteins. These proteins themselves can be covered with additional small

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chemicals. None of these molecular amendments change the underlying genetic code. But adding these chemical groups to the DNA or to the associated proteins, or removing them, changes the expression of the nearby genes. These changes in gene expression alter the function of cells, and the very nature of the cells them- selves. (p. 8–9)

Scientists have determined that these chemical processes are impacted by various environmental factors. Stress, nutrition, trauma, and exposure to toxic substances can all have an effect on the complex epigenetic dance that Carey describes. In fact, studies have shown that the microbiota that live in our gastrointestinal tracts can impact gene expression (Dalmasso, Nguyen, Yan, Laroui, Charania, & Ayyadurai, 2011). And we are still learning about how this affects our thoughts, feel- ings, and behavior. Epigenetics explains the differences in phenotype we sometimes see in the personalities of monozygotic twins, especially in the development of genetically linked personality disorders.

Neuropeptides and Opiate Receptors

We have already discussed the role of neurotransmitters in the regulation of mood and emotion. Another interesting development in the study of neurobiology and personality is the function of neuropeptides. In 1973, as a graduate student at Johns Hopkins, Dr. Candace Pert discovered the relationship between neuropeptides and opiate receptors that have revolutionized psychophar- macology and our understanding of mind-body medicine. Her work showed that “neuropeptides and their receptors form an information network within the body . . . neuropeptides and their receptors are a key to understanding how mind and body are interconnected and how emotions can be manifested throughout the body (Pert, 1986, p. 9).” Her work explained why people react with euphoria to drugs such as heroin. Heroin is an opiate that attaches to the opiate receptors in our cells. But that begged the question of why we had opiate receptors in the first place. Work by Pert and others have proven that our brains naturally produce more than 60 different chemical substances (called neuropeptides) that attach to these same receptors and affect our emotions, thereby implicating the pain receptors and neuropeptides in the manifestation of emotions.

Neuroscientists have long agreed that the limbic system (primarily the amygdala and the hypo- thalamus) are the parts of the brain most closely connected with emotions. Pert found that these areas have a 40-fold higher count of opiate receptors relative to other regions of the brain. Neuro- peptides and their receptors are also found in other areas of the body, such as the gastrointestinal tract (which may explain the term ‘gut feeling’) and the testes. In this respect, neuropeptides and receptors create a web of interconnectivity between the glands, immune system, and the brain, which may represent a “the biochemical substrate of emotion” (Pert, Ruff, Weber, & Herkenham, 1985, p. 820s). In addition, more recent studies have linked the neuropeptide/opiate recep- tors information network to behavioral dysfunctions (Inui, 2003) and eating disorders (Fetissov et al., 2008).

Pert’s body of work showed us that our emotions are not simply created by these chemical exchanges; rather, that through self-consciousness, we can override the system and create what she called “molecules of emotion” (Pert, 1997). So essentially, she is saying that we can influ- ence the quality of the tone of our neuropeptides by positive thinking—literally flooding our sys- tems with “happy” neuropeptides and thereby changing our thinking and feeling, and, by default, our personalities. Essentially, modern science is validating what William James said more than 100 years ago about the mind-body connection.

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CHAPTER 4 4.7 Assessment Methods in Neurobiological Psychology

Contributions Beyond Psychology and Future Directions With each new discovery and the development and expansion of highly synthesized theoretical models integrating neuroscientific findings with converging lines of research from various disci- plines, our understanding of personality has clearly increased. Neuroscientific and neurobiological models have been especially useful in their contributions to other theoretical models, providing a richer foundation for theory. Models that are not firmly anchored in biology and psychology, and that do not take social realities into account, will not accurately reflect the complex interactions that determine personality. Many theoreticians and researchers agree that all theories of person- ality should eventually be grounded in findings from neuroscience (a step that may be easier for some theories relative to others). Another distinct advantage of synthesizing the neurobiological perspective with other theories is that it avoids the problem of fragmentation, whereby one loses the interconnected aspect of each theoretical approach in terms of their influence on personality.

One challenge for the coming years will be how the neurobio- logical perspective handles the myriad of ethical issues that arise with advancing technologies and information sharing. It is inevita- ble that the genetic factors that predispose us to certain person- ality traits will be determined. We now have the technology to identify our genes. When, and if, science discovers how they are

linked with certain behavioral disorders, how will society react? The challenge will be to develop ethical guidelines for the use of this rapidly advancing technology of personality.

4.7 Assessment Methods in Neurobiological Psychology

As technology has improved and allowed for a more detailed examination of the brain, the field of neuroscience has progressed tremendously. Perhaps more than any other sub- discipline, the techniques used in this field have changed rapidly, thereby redefining what we know and can hypothesize regarding the brain’s involvement in the development of personal- ity. Some of these techniques are here reviewed, and we conclude with a brief overview of some of the potential problems with the assessment tools.

Electrical Stimulation of the Brain Electrical stimulation of the brain, using tiny electrodes, is sometimes used to map regions of the brain associated with different sensations and responses. For example, electrical stimulation of the temporal lobe produces specific memories. Although this process of activation by neural stimulation can alter the content of self-awareness, the implications of this research are as yet unclear. Still, neuroscientists have successfully demonstrated that stimulating certain regions of the brain can produce sensations, memories, and even emotions (e.g., Fried, Wilson, MacDonald, & Behnke, 1998).

Beyond the Text: Classic Writings

Renowned Harvard psychologist Steven Pinker has written a thoughtful essay for the New York Times, entitled “My Genome, My Self,” that reflects on the myriad of issues brought forth with the possibility of knowing your genetic composition. Read it at http://www.nytimes.com/2009/01/11/magazine /11Genome-t.html?pagewanted=1&_r=0&em

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CHAPTER 4 4.7 Assessment Methods in Neurobiological Psychology

Single-Cell Recording It is now possible to record activity in a single neuron in the brain, with this procedure broadly referred to as electrophysiology. This allows researchers to examine brain activity (e.g., the action potential) that occurs proximal to responses to different behaviors and stimuli. Studies are often conducted on species like the Aplysia snail, which have enormous neurons whose chemical com- position and functioning can be studied more easily than those of human neurons.

Neuroanatomical Studies We can add to our understanding of the brain by examining how brain injury and neurological disorders are reflected in behavioral, cognitive, and affective changes. Looking at neural anatomy in these cases allows researchers to create a map of brain function by correlating behavior with damage to particular brain regions (Robins et al., 1999). For example, neuroanatomical studies reveal that cerebellar damage is associated with impaired cognitive functioning in planning as well as in affect overregulation, which is apparent in lack of emotional response (flat affect).

Much of what we have learned from neuroanatomical studies comes from studying those who have suffered brain trauma in wars throughout the 20th and 21st centuries, where specific dam- aged regions of the brain (e.g., due to head trauma) were associated with certain behavioral changes that could be observed and documented (recall the story of Phineas Gage). In a revealing book, My Stroke of Insight: A Brain Scientist’s Personal Journey (2006), Dr. Jill Bolte Taylor describes her experience of having a stroke and what it was like to have her left, dominant hemisphere shut down, as well as the process of retraining one’s brain and regaining a level of functionality. This type of information can be much richer than the observational studies of animals who have had parts of their brain lesioned so that the resulting behavioral changes can be observed.

Brain Lesioning and Functional Neurosurgery Earlier in the 20th century, frontal lobotomies were sometimes performed on individuals with psychoses. This procedure dramatically altered the behavior and personality of the individual. It also demonstrated that destroying the frontal lobes resulted in a severe flattening of emotions and emotional insensitivity (R. Carter, 1998). Given the central role of emotions in personality, it is not surprising that this region of the brain appears to be especially central to personality function- ing. Obviously, the advantage when dealing with human examples is that one can have access to internal experiences (i.e., the thoughts and feelings of the patient) rather than simply relying on the behaviors, as would be the case when working with animals.

Case Studies of Neurological Disorders The study of neurological patients has provided fascinating information. Patients who have suf- fered strokes and accidents experience changes in personality. Likewise, in many neurological disorders such as autism, Parkinson’s, epilepsy, and Alzheimer’s, there may be a complete loss of the self and the appearance of new personality characteristics. For example, dementia of the Alzheimer’s type (AD) can be associated with paranoid tendencies in over a third of patients (e.g., Brink, 1983), and the paranoia appears to increase as AD symptoms progress (Ballard, Chithiramo- han, Bannister, Handy, & Todd, 1991).

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CHAPTER 4 4.7 Assessment Methods in Neurobiological Psychology

With Alzheimer’s dementia, the etiology involves loss of neuronal functioning (caused by, or coincident to, the accumulation of beta amyloid plaques), primarily in the hippocampus, an area known to be involved in the formation of memories. Thus, one reasonable assumption is that as memory functioning declines, individuals become less aware of what they have done (e.g., forget- ting where they put their money or something of value), and a possible result of the poor memory is that they can become suspicious of others (e.g., questioning who took their possessions). Some have also argued that the mechanism underlying paranoia is itself biological in nature. That is, there is a biological substrate of Alzheimer’s that is marked by paranoia (Wilkosz, Miyahara, Lopez, DeKosky, & Sweet, 2006). In either case, this provides some evidence of biological underpinnings of traits such as paranoia.

Neuropsychological Testing A number of tests, primarily paper-and-pencil, but also behavioral and computer-driven, have been developed to assess the brain’s functional abilities. These tests are typically administered and interpreted by a neuropsychologist whose training is in the area of brain and behavior rela- tionships. The tests are fully standardized (i.e., they must be administered, interpreted, and scored in the same way for everyone) and extensive normative data are available for compari- son (i.e., to see how others of the same age, education, race, etc.) perform on these tests. The neuropsychological tests are typically identified by the brain function that they primarily assess, including tests of memory, executive abilities, word finding, visual-spatial reasoning, and the like.

Electroencephalography (EEG) and Neuroimaging Various ways of measuring neural activity in response to stimulation (termed evoked potentials) and neuroimaging techniques are also useful tools in the neurosciences. Electrical signals can be measured with electroencephalography (EEG), which uses electrodes placed at various locations on the skull to record electrical patterns of brain activity. Evoked brain potential (ERP) is measured by presenting participants with specific stimuli and detecting resulting activity in the brain. The work of Eysenck in studying the relation between the reticular activating system and extraversion was largely based on EEG findings.

A variety of brain-imaging techniques afford scientists a window into the living brain. A few of these techniques follow (R. Carter, 1998).

• Magnetic resonance imagining (MRI): This technique magnetically aligns atomic parti- cles in the body, shoots them with radio waves, and records the radio waves that return. Computer software, computerized tomography (CT), then converts this information into three-dimensional images.

• Functional MRI (fMRI): This procedure goes beyond illuminating the basic anatomy, such as that captured with the regular MRI, by observing the activity of the brain in real time. The activity of neurons is fueled by glucose and oxygen metabolism. When an area of the brain is active, increased oxygen is utilized and rapid scanning with fMRI can show the flow of brain activity.

• Positron emission tomography (PET): In this method of brain scanning, radioactive isotopes are injected into the bloodstream and, similar to fMRI, brain areas that are activated can be seen in vivid color. Although impressive, the resolution is not as high as in fMRI. Researchers examining structural variations in a wide range of psychiatric condi- tions have used this technology.

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CHAPTER 4 4.7 Assessment Methods in Neurobiological Psychology

• Near-infrared spectroscopy (NIRS): This technique records the fuel being used up when certain areas of the brain are activated. Low-level light waves are aimed at the brain and the light reflecting back is measured. However, this method cannot get to the deepest layers of the brain.

• Magnetoencephalography (MEG): This technique is similar to measuring the evoked electrical potential of the EEG, but instead measures the magnetic field gen- erated by the electrical activity of the brain. Although prone to extraneous interference, it is fast and accurate in its representation of the brain.

• Single-photon emission computed tomography (SPECT): This technique uses gamma rays for imaging and pro- vides real three-dimensional data through the comput- erized reconstruction of two dimensional images from different perspectives. The technique is also similar to the PET scan because it involves the injection of radioac- tive tracer material visible to the gamma camera.

Current Challenges and Future Directions in Neurobiological Assessments As with any field of research, there is controversy with regard to the methods and the way they have been used. Some research- ers believe that showing pictures of the brain can be mislead- ing without the establishment of a strong empirical basis for their use, as this will help us to understand and interpret what is being imaged (see Robins et al., 1999). A challenge for the future is that the theoretical models keep pace with emerging technology.

Another important consideration is a standardization of these techniques. That is, when we think of employing one of these assessment techniques, the assumption is that there is one standard procedure for how to carry out the procedure and interpretation. However, there are different approaches to doing so. Consider, for a moment, capturing the brain’s reac- tion to a particular stimulus. Researchers must decide how to best capture this reaction and, if there are different ways of doing so, whether they would be expected to provide similar or different information. As an example, the brain’s reaction to a stimulus could be quantified in terms of: (1) the speed with which the brain responds (e.g., the elapsed time between the onset of the stimulus and the onset of measurable brain change), (2) the extent or intensity of the brain’s response (e.g., how many regions or what percent- age of the brain is responding to the stimulus), or (3) the duration of the brain’s response to the stimulus (e.g., the elapsed time between the onset of the measurable brain response to the cessation of that response). These reflect just some examples of how the brain’s response can be quantified, and interpretive difficulties arise when each approach provides different

Mikhail Basov/ iStockphoto/ Thinkstock; National Institute of

Mental Health, National Institutes of Health, Department of Health and

Human Services; Dr. Giovanni Dichiro, Neuroimaging Section, National

Institute of Neurological Disorders and Stroke/National Cancer Institute

Some of the more advanced imaging techniques are (a) MRI, (b) fMRI, and (c) PET scans, with their respective outputs depicted here.

a.

b.

c.

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outcomes. Thus, technology alone does not solve all of our problems. The role of theory is especially important in understanding how each of these approaches might contribute to our understanding of the brain’s response, and even in deciding whether one method of quantifica- tion should take precedence over other approaches.

When researchers are called upon to collect data from multiple sites, these issues are espe- cially important. For example, researchers involved in nationwide consortium studies examining Alzheimer’s dementia have created specific instructions for how to carry out and interpret MRIs.

Summary

Current neurobiological models attempt to account for personality by linking biologically based variation to psychological factors. Certain neurotransmitters are associated with vari-ous personality traits and may predispose the individual toward specific personality types. The examination of specific neurotransmitters, such as serotonin, has been useful in better under- standing their link to long-term mood states and traits.

Five distinct theoretical models were reviewed in this chapter: (1) Eysenck’s three-factor model, (2) Buss and Plomin’s three-factor temperament model, (3) Depue’s three-factor model, (4) Clon- inger’s unified biosocial theory of personality, and (5) Siever’s dimensional model. As seen with Eysenck’s work, sensitivity in the ascending reticular activating system may be more likely to evi- dence introverted behavior (and those with less sensitivity may be more likely to be extraverted).

Neurobiological evidence has contributed to our understanding of many different issues central to understanding personality, offering new insights into dreams, the unconscious, the process of attachment, and even our response to stress (flight or flight).

The neurobiological effects of trauma on personality are well documented. Behavioral geneticists are interested in isolating the underlying genetic mechanisms for certain personality traits, although the way they are expressed, termed phenotypes, is influenced by the environment. A moderate degree of variance in personality (approximately 50% of the variation in traits) may be attributed to genetic factors, though this appears to vary depending on the trait under consideration.

The tools of assessment within the neurobiological model are especially important to its contribu- tions to personality science, and have played a central role in both defining the field and shaping its future, though ethical and standardization challenges persist.

Key Terms

activity A child’s level of interaction with the environment, on a range from vigorously active to passive.

adaptability A child’s positive or negative approach to new stimuli in the environment.

affective neuroscience A growing branch of neuroscience that is shedding light on the emotional processes of personality, studying, for example, facial expression and the parallel responses in the brain.

ascending reticular activating system (ARAS) Area that Eysenck proposed regulates the flow of information and stimulation to the brain and impacts extraverted behavior.

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CHAPTER 4 Key Terms

autonomic nervous system The part of the nervous system that controls automatic functions.

axon The elongated portion of a neuron that is involved in sending a message.

Broca’s area Brain region that controls move- ments associated with speech production; damage to this area results in slow, labored speech.

central nervous system The part of the nervous system comprising the brain and spinal cord.

cerebellum Brain structure that regulates signals involving movements, thoughts, and emotions from other parts of the brain.

cognitive neuroscience A type of neuroscience concerned with brain-based theories of cogni- tive development.

critical period A period of development where the organism is most likely to be able to learn. This window for learning is less flexible than a sensitive period.

dendrites Hair-like structures that emanate from the soma of a neuron and are largely responsible for receiving messages.

dichorionic Twins that develop in separate placentas and chorions.

dizygotic (DZ) Fraternal twins who share 50% of their genetic makeup.

functional MRI (fMRI) Brain imaging technique that captures brain activity in real time.

genotype Underlying genetic material, includ- ing that which affects personality.

heritability A statistical calculation describ- ing the effect of genes and the proportion of observed variation that can be attributed to genes.

Human Brain Project Cognitive neuroscience project that aims to create a three-dimensional computer to simulate activity of the human brain.

interpersonal neuroscience Related to affec- tive neuroscience, but placing its emphasis on the primacy of interpersonal experience, this branch of neuroscience focuses on relation- ships; it considers the ways that the regions of the brain responsible for social perception and interpersonal communication are also critical for regulating body states, memory, and emo- tional processes.

magnetic resonance imaging (MRI) Three- dimensional imaging technique that uses magnets and radio waves to map regions of the body.

magnetoencephalography (MEG) Brain imag- ing technique that measures the magnetic field generated by the electrical activity of the brain.

monochorionic Twins that develop in a single placenta and chorion.

monozygotic (MZ) Identical twins who share 100% of their genetic makeup.

near-infrared spectroscopy (NIRS) Brain- imaging technique that uses low-level light waves to record energy used in certain areas of the brain.

neurogenesis The creation of new neurons.

neurons Specialized cells that make up the nervous system and function to communicate information.

neuroplasticity The ability of brain regions to change function over time.

neuropsychological tests Assessments admin- istered and interpreted by neuropsychologists to assess the functional abilities of the brain.

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CHAPTER 4 Key Terms

neurotransmitters Naturally occurring chemi- cals that carry information to other cells across the synaptic gap between neurons.

parasympathetic nervous system The part of the nervous system that controls the calming responses.

peripheral nervous system The part of the nervous system that connects the central ner- vous system to the rest of the body.

personality neuroscience Branch of neuro- logical sciences that investigates how brain processes influence the interactions between the environment and genes, and how these processes are linked to personality traits and variations in personality.

pharmacotherapy Therapy that uses drugs to treat mental disorders.

phenotype An observable characteristic related to both genetic and environmental influences.

positron emission tomography (PET) Brain imaging technique that uses radioactive iso- topes to capture active regions of the brain.

sensitive period A period of development when learning is most likely to occur because of biological priming for learning a certain behavioral pattern.

single-photon emission computed tomography (SPECT) Brain-imaging technique that uses gamma rays to construct three-dimensional images from two-dimensional images.

soma The cell body of a neuron.

somatic nervous system The part of the nervous system that controls sensation and movement.

stress This term entered the fields of psychol- ogy and biology when Selye (1956) began using it to mean “a physiological response that is inadequate to an environmental demand.”

sympathetic nervous system The part of the nervous system that controls arousal.

synaptic gap The space between two neurons where neurotransmitters are released.

Wernicke’s area Brain region that controls lan- guage comprehension; damage to this area often results in speech that is grammatically normal (there are complete sentences), but semantically deviant (the words chosen do not make sense).

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