Chapter 7 THE NEUROSCIENCE OF PERSONALITY
- Meditation is a way that you could be healthier and happier. Although some religious and
cultural traditions embrace meditation as a powerful spiritual practice, modern medical
research has traditionally scoffed at alternative treatments.
- Overall, the data suggest that regular meditation fundamentally changes how our brains work
and that its activation is related both to the emotions we feel and to how we respond to
stressful events. The researchers surmised that meditation makes people more open to
experiencing positive emotions and less reactive to negative emotions with the overall effect of
decreasing their anxiety and improving immune functioning- all of this without drugs!
- When it comes to understanding our biological functioning and personality, it’s like the question
of which came first, the chicken or the egg: Does your physiology determine our personality, or
does our personality determine our physiology?
- We may be born with a certain physiology that may cause us to develop certain traits, but the
environment can modify aspects of our personality. Perhaps the best way to think of our
physiology is as a package of potentialities for personality traits that may be devekoped,
discouraged, or even modified by our experiences.
- However, at the same time research such as the meditation study suggests that our behavior
also affects our physiology.
What is Neuroscience and How Do We study it?
- Researchers who explore the neuroscience behind personality focus on the brain and the
- The nervous system is made up of the central nervous system and the peripheral nervous
- The central nervous system includes the brain and the spinal cord whereas the peripheral
nervous system includes the somatic nervous system, which controls movements of the
muscles, and the autonomic nervous system which regulates smooth muscles (e.g., inner
organs), cardiac muscle, and glands.
- The autonomic nervous system is further divided into the sympathetic division and the
- The sympathetic division mobilizes energy (e.g., for fight or flight), whereas the
parasympathetic division supports systems that replenish the body’s energy stores (e.g.,
salivation, digestion, ect).
- The brain is protected by a bath of cerebrospinal fluid (CSF) that cushions the delicate brain and
also flows through spaces in the brain called ventricles. CSF is similar to blood plasma, and is
continually produced, circulated and reabsorbed through the brain and the ventricles.
- The brain contains a number of structures and systems that control everything from thinking,
reasoning, learning, and memory, to breathing, sleeping and eating , to movement and the
processing of sensory information, to the experience of emotions. Because all of these parts are
crucial for basic functioning, we should not expect to see large differences among people.
- However, individual can vary in all kinds of ways, from how they may respond to stress (e.g.,
heart palpitations, sweating) to what they think is happy or sad, to how they respond to
hormones and drugs.
- Researchers hypothesize that differences in bodily responses, brain structure, brain activity and
biochemical activity are all related to individual differences in personality. Bodily Responses
- When our body responds to arousing events in the environment it is the autonomic nervous
system that responds. When aroused, the sympathetic division responds by increasing heart
rate, blood pressure, blood flow to the extremities, respiration, sweating, and muscle activity.
- Sweating is measured by galvanic skin response (GSR) which is a measure of skin conductance
or how quickly a slight electrical current passes through two points on the skin. The faster the
conductance of the current, the more moisture is present that indicates greater arousal.
- Muscle activity is measured by electromyography (EMG) or myoelectric activity, which
estimates the electrical impulses of the muscles during contraction and relaxation. EMG is often
used in biofeedback to train people to perceive muscle contractions so that they can learn to
relax their muscles.
- In the past, the only way of studying differences in brain structure and cells was through
dissecting the brain after death. During an autopsy the brain may be removed and sections of
tissues preserved for cytological (cell) study.
- Today, through the advent of more sophisticated techniques we can study the structure of a
living human brain through noninvasive procedures.
- For example, computerized tomography (CT), called a CT scan, takes a high-resolution x-ray
picture of the brain By looking at thin cross sections of the brain- often less than a millimeter!-
we can detect abnormalities or differences in the brain tissue. (This same technique was once
called computer axial tomography [CAT] or CAT scan).
- Magnetic resonance imaging (MRI): a high-resolution three-dimensional picture of the brain
tissue obtained by the use of radio frequency waves. First, a strong magnetic field causes the
nuclei of some atoms to resonate. Then radio frequency waves are used to detect the activity of
these atoms. Because hydrogen atoms are present in all tissues but in varying concentrations,
the pattern of resonance formed by the hydrogen atoms forms a multidimensional picture of
- Both CT scans and MRIs can detect only static pictures of the brain- that is, pictures of brain
structure at one moment in time.
- Measures of brain activity are ways of looking for differences in brain structures while the brain
is stimulated. Often, participants are given a mental task to work on or other stimuli to react to
while measures of brain activity are taken.
- One early technique of studying brain activity is cortical stimulation. Using either electrodes
implanted in the brain or direct electrical stimulation of parts of the brain, the patient is awake
and can report on sensations as various parts of the brain are being stimulated.
- Today, we are able to sue less invasive procedures.
- For instance, in an electroencephalogram (EEG) electrodes are placed on the scalp to monitor
electrical activity of the brain.
- When electrical activity of the brain or other part of the nervous system is measured in response
to a specific stimulus, this is called an evoked potential (EP).
- Both EEGs and EPs indicate amount of brain activity in response to a stimulus. However, the
newer techniques identify the exact location of brain activity.
- In positron emission tomography (PET), called a PET scan, a slightly radioactive glucose like
substance with a very short half-life (rate of breakdown) is injected into the brain and the person is placed in a scanner similar to a CT scanner. Active regions of the brain use up more
glucose than inactive regions and, with the aid of computer enhancement, scans of these rgions
appear in different colors related to their activity level.
- The most detailed view of brain activity at a cellular level comes from functional magnetic
resonance imaging (fMRI)
- Functional magnetic resonance imaging (fMRI): a high-resolution three-dimensional picture of
brain activity over time using blood oxygen levels. Color enhancement is used to identify
amount of activity across many regions of the brain.
- Though the use of fMRI for personality research is on the rise, there are some notable problems with
fMRI research. One problem is timing of response. When viewing a stimulus, our thoughts react within
milliseconds whereas blood flow takes about 2 seconds. This makes it difficult to pinpoint the precise
area that fired at the exact moment of a thought or reaction.
- Another problem is that the procedure is time-intensive and the equipment expensive so that often
experiments use only a small number of participants Small sample sizes make it difficult to find a
reliable and significant effect.
- A third problem called the nonindependence error is that researchers may unintentionally bias their
results by not independently selecting which brain areas to correlate wit, say, personality
characteristics or other variables.
- Lastly, confounds such as time of day and nervousness of participants can also affect the results of
- One of the newest techniques for studying brain activity is transcranial magnetic stimulation
- Transcranial magnetic stimulation (TMS): using an electrical current to disrupt or enhance
neuron functioning to pinpoint with greater accuracy than other techniques an exact area of brain
- With TMS a brief electrical current passes through a coil placed on the head. The magnetic field
disrupts the regular activity of the neurons, sometimes impairing and sometimes enhancing
function. By carefully mapping parts of the brain that are stimulated and noting what kind of
functioning is disrupted, researchers are able to pinpoint with greater accuracy than cortical
stimulation or EP the exact area affected.
- There is one major problem with interpreting the results of brain scan research: what exactly
does it mean when an area reacts in response to certain stimuli? According to critics of brain
localization techniques, it could mean a number of things.
Neurotransmitters are chemicals released by neurons to inhibit or excite the next neuron into
- Neurotransmitter help transmit signals through the nervous system. Some important
neurotransmitters are norepinephrine, epinephrine, dopamine, and serotonin.
- These all have a similar molecular structure, so that drugs that affect one tend to affect all of
them. Norepinephrine (noradrenaline) and epinephrine (adrenaline) are also considered stress
- They help the body deal with threat by increasing blood flow to the muscles which increases
heart rate and blood pressure.
- Dopamine is related to feelings of pleasure and helps regulate movement, learning, attention,
- Serotonin is involved with mood regulation, arousal, the control of sleeping and eating and pain
regulation. Depression, anxiety and other mood disorders are related to how the body
processes serotonin. - The enzyme monoamine oxidase (MAO) regulates, to some degree, the availability of dopamine,
norepinephrine, and epinephrine in the system.
- Norepinephrine and serotonin may also be related to symptoms of depression.
- Antianxiety drugs work by mimicking another neurotransmitter, gamma-aminobutryric acid
(GABA), an inhibitory neurotransmitter.
- Researchers may study neurotransmitters and the systems that process them by having
participants engage in a task or activity and monitor the fluctuations in these chemicals.
- When it is impossible to directly measure the level of neurotransmitters- as with
norepinephrine, for example- researchers indirectly monitor how the neurotransmitter is being
used by measuring known byproducts of neurotransmitter metabolism.
- Another way is through a challenge test in which researchers administer a drug that is known to
either increase or decrease a neurotransmitter’s functioning and monitoring the impact of this
new substance on reactions presumed to be related to the neurotransmitters.
Research Methods Illustrated: Correlational Designs II: Scatterplots, Correlations, and the
Alleged ‘Voodoo Science” of fMRI Studies.
Scatterplots or scattergram: a two-dimensional graph that shows the relationship between two
- They show the scatter or spread of the data.
- Many brain-imaging studies will use scatterplots to illustrate their results. Each point represents
a participant in the study.
- The line through the clouds of points is called a linear regression line and it estimates our best
guess of how we can predict y-values from x-values.
Neurological Theories of Personality
- Hans Eysenck noted that even as we recognize that a substaintial portion of our personality is
inherited ‘there must be biological intermediaries between DNA and personality, and these
intermediaries should be specified by theory and investigated’. These biological intermediaries,
what Eysenck’s technology was not sufficiently advanced in 1947 to detect, are physiological
- Despite bigger and better and less invasive techniques and even with the ability to decode the
smallest gene, protein, and neurotransmitter, scientists are not able to find consistent
physiological differences that relate in a clear way to differences in personality characteristics.
- It may be that our techniques are not up to the task or it may be that aspects of the human
nervous system interact in complicated ways that we have yet to untangle.
- Maybe biology has the biggest impact at a broader, more general level of personality, called
- Temperament: a set of personality characteristics that are
1. Relatively stable across the life span
2. Expressed through general energy level
3. Present from early childhood
4. Similar in other species of animals
5. Present at birth, at least in a general way
6. Determined by genetic factors
7. Changeable with maturation and experience In their search for the biological basis of personality nearly all major personality typologies
converge on three primary temperaments, or clusters of related personality traits:
Extraversion: Positive emotion, reward sensitivity, social rewards, sociability, approach.
Neuroticism: Negative emotion, anxiety, punishment sensitivity, withdrawal.
Impulsivity: Psychoticism, lack of constraint, sensation seeking, novelty seeking, lack of
conscientiousness, lack of agreeableness.
- There has been striking similarity in the various models that researchers have proposed. For
example, Eysenck’s Psychoticism, Extraversion , and Neuroticism model (PEN model), the five-
factor model, the Big Five, Grays RST and Cloninger all posit at least two of these three
dimensions as part of their theories.
- However, both the FFM and the Big Five split Eysenck’s Psychoticism factor into Agreeableness
Table 7.2 Correspondence Among Three Personality Clusters and Major Trait Theories
Theory Extraversion Neuroticism Impulsivity
Eysenck Extraversion Neuroticism Psychoticism
Gray Behavioural Approach Behavioral Inhibition
Five Factor Extraversion Neuroticism Low Conscientiousness
Cloninger Reward Dependence Harm Avoidance Novelty Seeking
Eysenck’s PEN Model
- When Eysenck first started working in the 1940s, he was unusual in his desire to build a
personality theory based on experimental findings. Further, he believed that a comprehensive
theory should explain how people developed their personalities as well as predict consequences
and outcomes of various personalities.
- The three dimensions—Psychoticism, Extraversion, and Neuroticism—form the PEN model. This
model is used to describe personality. People can be high or low on each of the three factors.
Overview of Eysenck’s Three Dimensions
People who are high in this factor, extroverts, tend to be sociable, popular, optimistic, and
Those low in extroversion- introverts- tend to be quite, introspective, reserved and reliable,
and to have a few close friends.
Essentially, extraversion refers to how outgoing people are, to both the social and the
Neuroticism is contrasted with emotional stability.
People high in this factor tend to be distressed, insecure, and upset in many areas of life.
They are chronically worried, nervous and moody, hold a low opinion of themselves, and
find it difficult to get back on an even keel after an upsetting experience.
In contrast, emotionally stable people are even-tempted, calm, relaxed, carefree, unworried
and somewhat unemotional and return to their natural state quickly after an emotional
experience. 3. Psychoticism
We think of Psychoticism as being antisocial and contrast it with ego control
People high in Psychoticism tend to be loners, egocentric, troublesome, manipulative,
impulsive, uncooperative, hostile and withdrawn and do not fit in anywhere.
In contrast, people low in Psychoticism tends to be altruistic, socialized, empathetic and
conventional. They care about others and are able to control their impulses to a greater
extent than those high in psychoticism.
- Eysenck drew on at least three pieces of evidence to support his view that these differences in
personality are genetic and biological.
1. First, cross-cultural universality in traits implies a strong biological component. After all, we
would expect that large differences in culture and environment would produce different kinds of
personality factors. The fact that three factors of Psychoticism, Extraversion and Neuroticism
occur in such diverse culture suggests a biological, rather than cultural explanation.
2. Second, people show tremendous consistency in these three traits over time, despite changing
environments. Responses and habits might change over time and situations, but traits do not.
3. The third piece of evidence is that robust finding that Extraversion, Neuroticism and
Psychoticism each have moderate heritability. As Eysenck state, “genetic factors cannot directly
influence behavior or cognitions, of course and the intervening variables must inevitably be
physiological, neurological, biochemical or hormonal in nature”.
- Although Eysenck suspected that arousal and attention were involved with all three of his
factors, he admitted that the research evidence did not suggest a clear hypothesis for a
biological explanation of psychoticism.
Neurology of Extraversion
- Eysenck thought that the main difference between introverts and extraverts had to do with
arousal and on that score he was right. He considered two possibilities: that introverts and
extraverts differed in arousal level or in arousability.
- Eysenck thought that introverts had greater cortical arousal than extraverts, particularly in the
ascending reticular activating system (ARAS), a pathway transmitting signals from the limbic
system and hypothalamus to the cortex. The ARAS processes the more cerebral aspects of
arousal or emotion. Activation in the ARAS can make a person alert and mentally sharp or
sluggish and mentally dull.
- Because of their hypothesized overaroused baseline conditions, introverts act more restrained
and inhibited. They avoid conditions that would aggravate their already overstimulated
conditions, preferring to stay to themselves and engaging in more quite activities.
- In contrast, the system of extraverts, Eysenck reasoned, lets in too little stimulation so that their
underaroused condition leads them toward more stimulating and unrestrained behaviors.
- Basically, extraverts are more outgoing and engaged with the world to raise their naturally low
level of arousal. In this way, both extraverts and introverts attempt to regulate their own
arousal striving to find their comfort zone: an optimal level of arousal.
- Over 1000 studies have been conducted testing Eysenck’s theory of arousal with no success,
claiming that his hypothesis in not true.
- However, there is a significance difference in how extraverts and introverts respond to
moderate stimulation, suggesting that the key difference between them is in their arousability
or sensory reactivity. - Arousability: in physiology, how reactive people are to stimulation; an important difference
between extraverts and introverts.
- One study found that people studying in the quite study spaces of their college library- spaces
with individual carrels, small tables- tended to be introverted. Extraverted preferred to study in
the noisy but highly sociable areas of the library.
- People’s noise preferences and performance outcomes depend on their optimal level of arousal
as determined by their personality.
Neurology of Neuroticism
- Eysenck hypothesized that physiological arousal could also account for individual differences in
- he thought that Neuroticism had to do with stability or instability of the sympathetic nervous
system (i.e. those parts of the brain that are involved in emotional regulation such as the
hippocampus, amygdala, cingulum, septum and hypothalamus)
- Basically, the vulnerability of people high in Neuroticism to negative emotions such as fear and
anxiety was due to an extra sensitive emotional or drive system.
- Extraversion and Neuroticism are similar in that both involve arousal; however, the big
difference is in the valence or quality of that arousal.
- Extraversion is marked by positive arousal such as excitement and energy, whereas Neuroticism
is marked by negative arousal such as fear and anxiety.
- People high in Neuroticism show an increase in heart rate in response to an intense stimulus. So
do introverts. However, people high in Neuroticism but not introverts show greater startle
response to fearful pictures.
- These findings suggest that people high in Neuroticism may be more sensitive to negative
emotions in particular and not to arousing situations in general, the way that introverts are.
- All in all, there is no support for Eysenck’s hypothesis that Neuroticism is related to activation in
the sympathetic nervous system.
Reinforcement Sensitivity Theory (RST)
- An alternative theory was proposed by Jeffrey Gray.
- For Gray, personality is the variation in the functioning of brain systems.
- Gray’s idea was to
1. Identify brain-behavior system that accounted for imp