ArticleAllemand, M., Steiger, A. E., & Hill, P. L. (2013). Sta.docx

Article
Allemand, M., Steiger, A. E., & Hill, P. L. (2013). Stability of
personality traits in adulthood: Mechanisms and implications.
GeroPsych: The Journal of Gerontopsychology and Geriatric
Psychiatry, 26(1).
· The full-text version of this article is available through the
EBSCOhost database in the Ashford University Library. In this
article, the authors discuss the the Five Factor model and the
stability of personality traits over time in adulthood.
Hurley, D. (2013). Trait vs. fate. Discover 34(4) p. 48-55.
Retrieved from the EBSCOhost database.
· In this article, the author discusses the research done by
Meaney and Szyf on the genetic effects of life experiences,
including the experiences of of parent and grandparents.
Weaver, I. C., Cervoni, N., Champagne, F., D'Alessio, A.,
Sharma, S., Seckl, J., Dymov, S., Szyf, M., & Meaney, M.
(2004). Epigenetic programming by maternal behavior. (Links
to an external site.)Links to an external site.Nature
Neuroscience, 7(8). p847-854.
· This article describes how the licking and nursing behaviors
(rated as attentive to nonattentive) impacts the physiology and
behavior of their offspring.
Webster, M. (2013). The great rat mother switcheroo (Links to
an external site.)Links to an external site. [Blog post].
Retreived from http://www.radiolab.org/story/261176-the-great-
mother-switcheroo/
· This blog provides an easy to understand discussion of the
epigenetic experiments discussed in the Hurley and Weaver, et
al. articles.
Multimedia
1. Walters, Pat. (Producer). (2012, November 19).
Inheritance (Links to an external site.)Links to an external site.
[Audio podcast]. Retrieved from

http://www.radiolab.org/story/251876-inheritance/
· This podcast includes the information from The great rat
mother switcheroo blog and provides an easy to understand
discussion of the epigenetic experiments discussed in the two
assigned articles.
Recommended Resources
Article
1. Susser, E., Hoek, W. H., & Brown A. (1998).
Neurodevelopmental disorders after prenatal famine: The story
of the Dutch famine studyLinks to an external site.. American
Journal of Epidemiology 147(3), 213-216. Retrieved from
http://aje.oxfordjournals.org
· The authors of this article provide an overview of the Dutch
Famine Study, one of the original epigenetic studies.
Multimedia
1. Griffen, C. [Courtney Griffen]. (2012, February 23).
Epigenetics and the influence of our genesLinks to an external
site. [Video file]. Retrieved from
https://youtu.be/JTBg6hqeuTg
· In this video, Courtney Griffen discusses the interchange of
genes and environment as well as the role of epigenetics in the
expression of those genes in our environment. Her presentation
includes a discussion of the structure of DNA and the role of
histones and epigenetics markers in human cells. This video has
a transcriptLinks to an external site..
2. Obenauer, W. (2015, June 6). The big five personality
model (Links to an external site.)Links to an external site..
[Video file]. Retrieved from
htps://www.youtube.com/watch?v=gtiRNxd_qL4
3. Peterson, J. B. (2017, March 11). 2017 Personality 14:
Introduction to traits/psychometrics/the big 5. (Links to an
external site.)Links to an external site. [Video file]. Retrieved
from https://www.youtube.com/watch?v=pCceO_D4AlY
4. The health-and-fitness. (2016, August 17). Understanding the

big five personality traits with examples (Links to an external
site.)Links to an external site.. [Video file]. Retrieved from
https://www.youtube.com/watch?v=8Jjyc-htz50
Interactive Modules
1. University of Utah Health Sciences: Learn.Genetics Genetic
Science Learning Center. (2015).Lick your rats (Links to an
external site.)Links to an external site. [Interactive activity].
Retrieved from
http://learn.genetics.utah.edu/content/epigenetics/rats/
· This interactive activity allows the students to explore in a
game-like environment the scientific studies that have been
done on mother rats. This activity contains the same content as
the required readings for this week.
Website
1. Truity Psychometrics LLC. (n.d.). The big five personality
test (Links to an external site.)Links to an external site.
[Measurement instrument]. Retrieved from
http://www.truity.com/test/big-five-personality-test
· This web resource provides an online assessment based on the
Big Five Personlity theory. It is an opportunity for students to
apply the theory to their own personalities to assess its value
and accuracy.
First Post
Company executives must do their best to create the most value
for all stakeholders within their company. There are both
internal and external factors that can help build a company's
worth and impact a company's stock price. Analysis and
comparison among other companies is a tool used by financial
analyst's in order to figure out these internal and external
factors. Valuation by comparables is one of these tools that can
be used. Brealey, Myers, & Marcus (2018) defines valuation by
comparables: "when financial analysts need to value a business,

they often start by identifying a sample of similar firms. They
then examine how much investors in these companies are
prepared to pay for each dollar of assets or earnings" (p. 204).
This is just one tool that is utilized to determine whether a
company puts forth the highest value for stakeholders.
Comparably Company Analyses or Comps is another tool that is
also used to value a company. There are many advantages and
disadvantages to using this tool. Some of these advantages
include: easy to calculate, easy to communicate across market
participants, determines a benchmark value for multiples used
in valuation, and provides a useful way to assess market
assumptions of fundamental characteristics baked into
valuations (Comparable Company Analysis, n.d.). However,
there are some disadvantages to this tool, such as the fact that it
is easily influenced by temporary market conditions and can be
difficult to find appropriate comparable companies for reasons
like too few companies to compare.
Utilizing these tools to build a company's worth is a smart and
strategic move. Silva (n.d.) does a great job at providing insight
on making strategic decisions as a business owner. He states
"Obtaining a business valuation is one of the most important
things you can do to gain a competitive edge and increase your
company’s current and future value." Using the tools to analyze
the strengths and weaknesses of a company can provide a
different perspective in order to ensure success.
References
Brealey, R. A., Myers, S. C., & Marcus, A. J. (2018).
Fundamentals of Corporate finance (9th ed.). New York, NY:
McGraw-Hill.
Comparable Company Analysis. (n.d.). Retrieved February 05,
2018, from http://www.streetofwalls.com/finance-training-
courses/investment-banking-technical-training/comparable-
company-analysis/

Silva, F. (n.d.). Business Valuation: The Strategic Decision
Making Tool. Retrieved February 05, 2018, from
http://www.prairiecap.com/business-valuation-the-strategic-
decision-making-tool
Second Post
While financial statements can give potential investors a great
deal of information about the financials of a company, this
information may or may not tell the whole story. Yes, the
financial statements allow investors to measure the performance
of the company by evaluating different indicators such as the
earnings per share (EPS) or the price to earnings (P/E) ratios
but there are some cases where companies that do not have any
profits or when there is a rapid increase in revenues which
render certain simple valuation methods useless (Zarzecki,
2010). For this reason, other aspects of the company must be
examined as well. Information such as the size and quality of
the company, common competitors, marketing strategies,
management structure, type of customer base, and future
outlook are all factors that play a distinctive role in the
perceived valuation of the company by potential investors.
As we have learned, one of the main goals of a corporation’s
financial managers is to increase market value. Since there is
no sure-fire way of increasing market value, implementing some
fundamental strategies can prove to be effective in creating the
greatest opportunity to increase the value.
While there are many decisions that executives face in terms of
increasing a company’s value, one of the most complex is when
and where to invest their capital. In making these decisions, the
opportunity cost of capital or the minimum acceptable rate of
return must be considered (Brealey, Myers, & Marcus, 2018,

p.30). Risky investment projects can prove to be rewarding if
the rate of return yields a higher rate than the cost of capital,
thus increasing value. On the other hand, less risky investments
tend to be safer and more stable but at the cost of a smaller rate
of return. Although high risk investments can seem attractive,
the goal of the company is to remain profitable and smart
decisions must be made to balance the risks and ensure the
survival of the company, not only in the short-term, but more
importantly, the long-term.
References
Brealey, R. A., Myers S. C., & Marcus, A. J. (2018).
Fundamentals of Corporate Finance. New York, NY: McGraw-
Hill.
Zarzecki, D. (2010). Valuing internet companies. selected
issues. Folia Oeconomica Stetinensia, 9(1), 105.
http://dx.doi.org.ezproxy.liberty.edu/10.2478/v10031-010-0015-
5
John Foxx/Stockbyte/Thinkstock
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
• 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
Lec81110_04_c04_097-132.indd 99 5/21/15 12:38 PM
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.
Lec81110_04_c04_097-132.indd 100 5/21/15 12:38 PM
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
Lec81110_04_c04_097-132.indd 101 5/21/15 12:38 PM
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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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
Lec81110_04_c04_097-132.indd 103 5/21/15 12:38 PM
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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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
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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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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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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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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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
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CHAPTER 4
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
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CHAPTER 4 4.5 Personality Neuroscience: An Overview of the
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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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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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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CHAPTER 4
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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CHAPTER 4
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
Personality
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CHAPTER 4
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.
Personality
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CHAPTER 4
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

Personality
Lec81110_04_c04_097-132.indd 124 5/21/15 12:38 PM
CHAPTER 4
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.

ArticleAllemand, M., Steiger, A. E., & Hill, P. L. (2013). Sta.docx

ArticleAllemand, M., Steiger, A. E., & Hill, P. L. (2013). Sta.docx

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ArticleAllemand, M., Steiger, A. E., & Hill, P. L. (2013). Sta.docx