Biological systems and processes in
Evolutionary/genetic perspectives do not generally account for the biological
mechanisms between genes and personality.
Theorists use biological processes in an attempt to fill in the gap between
personality and genetics by inferring, theorizing and researching
biological links with behaviour
Anatomical approach examine functions of various structures of brain.
The biochemical approach examines hormones & neurotransmitters.
This is a complex, difficult area of personality with no clear and
simple answers. At a second year level, the expectation here is to get
your head around the basic principles that have been proposed. Also,
look for places where you can link the theories to each other and to
other perspectives of personality. In this way, the content of the
biological perspective is most likely to make sense and become part of
your understanding of human psychology.
Eysenck: Extraversion and Neuroticism
One of the pioneers in attempting to relate personality to biology was
the British psychologist Hans Eysenck (e.g. 1967, 1987). His theory is
complex and has evolved over the years, but one of its basic assumptions
is that the human brain has excitatory and inhibitory neural mechanisms.
A basic assumption is that the human brain has excitatory and inhibitory
Excitatory --> individual alert, awake, aroused
Inhibitory mechanisms --> sleepy, drowsy, sluggish
Balance between the two produces level of psychological arousal at any
Eysenck hypothesised balance regulated by ARAS
Ascending Reticular (aka Reticulocortical) Activating System which is a
structure in the brain stem.
Research suggests that function of ARAS is to regulate the amount of
information or stimulation that goes into the brain. It activates and
deactivates higher parts of the brain (cerebral cortex) and is involved
in maintaining alertness and concentration and in controlling the
Eysenck stated each individual’s ARAS functions differently:
- ARAS that lets in LOTS of stimulation --> introvert
- ARAS that cuts brain off from stimulation --> extrovert
This may seem counterintuitive at first but think about it. A person
whose ARAS causes him/her to be to be chronically overraroused is an
INTROVERT. If you are getting lots of sensory input you AVOID
stimulation as you already have more than you need. So, avoid loud
noises, social stimulation, noisy parties and exciting situations.
However, a person whose ARAS causes him/her to be to be chronically
underaroused is an EXTRAVERT. He or she will CRAVE stimulation looking
for sociable situations, loud parties and may be a sensation seeker.
The resting level of ARAS activity is higher for introverts than
- naturally more aroused
- prone to overarousal
- stimulus shy
- naturally underaroused
- seek arousal
- stimulus hungry
Evidence for ARAS theory
- Animal research
- Laboratory research
- extraverts chose louder noise
- extraverts take more pauses during in a repetitive task (due to
- Drugs: introverts require more depressant to get 'unalert'
- Saliva production (Lemon Juice Test)
THE LEMON JUICE DEMONSTRATION
- It has been reported that introverts produce more saliva than do
extraverts (Corcoran, 1964, in Phares, 1991):
- Tie a thread to the centre of a double-tipped cotton swab so that it
hangs perfectly horizontal
Person swallows three times then put one end of the swab on the tongue,
holding it there for 30 seconds
- Then 4 drops of lemon juice are placed on the tongue. After swallowing
the person places the other end of the swab on the same portion of
tongue for 30 seconds.
- Swab will remain horizontal for extraverts, hang down on the lemon juice
end for introverts (indicating a relatively large amount of saliva
produced in response to the lemon juice)
- Nonetheless, other more sophisticated tests give conflicting results.
Eysenck’s theory is an impressive effort to conceptualize and test brain
functioning and personality. It is the oldest modern comprehensive
attempt to create model of personality based on biological processes. It
was however developed prior to modern methods of testing brain
functioning, thus may be wrong in some respects. And it is certainly
likely to be an oversimplification. The ARAS is a not as GENERAL a
system as was first thought. It does not just turn neural stimulation to
the brain on and off like a tap (Zuckerman, 1991). Differing levels of
arousal across different parts of the brain are typical.
Gray's BAS/BIS Theory
Many theorists in this area believe that there is a set of brain
structures that cause animals to move towards things they desire. We are
going to focus on the work of neuropsychologist Jeffrey Gray (e.g.
1981). Gray has tried to improve on Eysenck’s theory. Gray extrapolated
the findings of his early research on animals to human personality.
Gray, like Eysenck, proposes that personality is based on the
interaction of two basic systems in the brain:
1. The first system is the Behavoural Approach system (BAS): this is the
approach motivation system or the GO system. The approach system causes
one to be both sensitive to potential rewards and motivated to seek
those rewards. Attraction to a person or a chocolate cake and a desire
to approach the person or cake comes from this system (BEHAVIOURAL
2. The second system is the Behavioural Inhibition System (BIS): this is
the avoidance motivation or STOP system. This is the system that causes
one to be sensitive to potential punishment and motivated to avoid those
punishments. Fear of rejection by someone you fancy or fear of a snake
and the motivation to avoid these things comes from this system.
• BAS / BIS independent
• Behavioural Approach/Activation System
• positive emotions (hope, joy) (anticipation of good events)
• high BAS (reactivity) 'impulsive'
• low BAS (reactivity) 'not impulsive'
• leads to sociopathy if no inhibition (whereas Eysenck says it is a
combination of extraversion and emotional instability)
Work by Richard Davidson (1992, 1995) has shown that positive feelings
involve activity in the left frontal lobe of the cortex. Higher levels
of frontal activity have been found to occur in adults presented with an
incentive. Davidson and colleagues (p. 163) assert that 1. The tendency
to experience happiness relates to the Behavioural Approach System and
2. That the system is partly based in the left frontal cortex.
BIS: behavioural inhibition system
• inhibits movement towards goals
• responsive to cues of punishment or danger
• high BIS high trait anxiety
• low BIS low trait anxiety
• leads to anxiety-based disorders (which Eysenck says are a combination
of high introversion and emotional instability)
• Research on cortical activity shows an increase in activity in the
RIGHT frontal areas of the cortex when people are anxious, fearful or
Biological bases of disorders
oversensitive BIS - highly anxious
oversensitive BIS or undersensitive BAS - depression
overactive BAS or BIS deficits - antisocial
Hormones & Personality
Uses endocrine system, rather than brain processes, to explain
Our body chemistry also influences our personality. Several studies have
revealed a link between hormone levels and aggression for example (e.g.
Berman, Gladue, & Taylor, 1993; Van Goozen, Frijda, & Van de Poll,
1995). See Farrington 1994.
Females have 40 nanograms of testerone in each deciliter of their blood;
males have 300 to 1000 nanograms of testosterone per deciliter of blood
Mothers exposed to male hormone during pregnancy had children who were
more likely to self-report aggression as a way of dealing with
interpersonal conflict, as opposed to their same sex siblings (Reinisch,
1981). This was found for both boys and girls, and suggests that
hormonal influences alone may impact upon aggressiveness. One caveat
however is that this study used self-report measures of aggression.
In a study by Dabbs and Morris (1990), men higher in testosterone were
found to be more likely to abuse alcohol and drugs, assault people, be
dominant, have large numbers of sexual partners, be single, or divorced
if married, and have trouble with teachers, parents, classmates whilst
growing up. Mostly these effects were stronger for low SES, perhaps
because high SES socializes out undesirable behaviours.
As mentioned, females also produce testosterone. In a study by Dabbs,
Ruback, Frady, Hopper and Sgoritas (1988) female prisoners who had
committed violent crimes which were unprovoked were founder to have
higher levels of testosterone than females who had committed violent
crimes due to provocation or had committed non-violent crimes.
It should be noted however that the findings on the links between
testosterone and aggression are by no means conclusive. It has been
suggested, for example, that increased testosterone level may be the
result of aggression rather than the cause of it (Zuckerman, 1991).
Levels of testosterone are altered by situational factors, e.g.
increases following success at a competitive event, sexual intercourse,
and decreases following failure.
Another hormone implicated in personality is cortisol. People who suffer
from severe stress, anxiety and depression tend to have very high levels
of cortisol in their system. This would appear to be a RESULT of stress
and depression rather than a CAUSE of it.
Neurotransmitters and personality
Communication between neurons in the brain is based upon substances
called neurotransmitters. Some of the neurotransmitters you may be
familiar with are epinephrine, norepinephrine, dopamine and serotonin.
Norepinephrine for example is likely to be involved in both anxiety and
High levels of norepinephrine have for example been associated with
anxiety-proneness, dependency and sociability. On the other hand, low
levels of norepinephrine are associated with disinhibition & impulsivity
Criminals have been found to have low levels of epinephrine and
The neurotransmitter, dopamine, is implicated in bodily movements,
amongst other things. A lack of dopamine is associated with Parkinson’s
disease (l-dopa and Sacks).
The enzyme MAO which I mentioned early and which regulates the breakdown
of the neurotransmitters serotonin, norepinephrine and dopamine has been
found to be implicated in aggression, extraversion, sensation seeking,
such that low levels of this enzyme lead to increased levels of
aggression, extraversion, and sensation seeking.
Another neurotransmitter, serotonin has a role in the inhibition of
behavioural & emotional impulses. Low serotonin levels are implicated
with obsessive worry, depression, irrational anger, and chronic
pessimism. Marazzitti, et al. (1993) found that highly aggressive
individuals had reduced levels of serotonin when compared with controls.
High serotonin levels are associated with compulsive behaviours and
obsessive tidiness. However the workings of serotonin are extremely
complex and not fully understood. Dean Hamer, who has researched
serotonin extensively, suggests that serotonin is a chemical that ABETS
rather than alleviates anxiety and depression. Serotonin levels have
been linked to aggression such that when serotonin levels rise so to
does aggression (Wright, 1995).
Burger, J. M. (1993). Personality (3rd ed.) Pacific Grove, CA:
Carver, C.S., & Scheier, M.F. (2000). Perspectives on Personality
(4th ed.) Needham Heights, MA: Simon & Schuster.
Funder, D. C. (1997). The personality puzzle. New York: W. W.
Ornstein, R. (1993). The Roots of the Self: Unraveling the mystery of
who we are. New York: HarperSanFrancisco.
Phares, J.E. (1991). Introduction to Personality (3rd ed.). New
York: Harper Collins.
Ridley, M. (1999). Genome: The autobiography of a species in 23
chapters. London: Fourth Estate.