Neural AO1
Serotonin
Serotonin is thought to reduce aggression by inhibiting
responses to emotional stimuli that might otherwise lead to
an aggressive response. Low levels of serotonin in the brain
have been associated with an increased susceptibility to
impulsive behaviour, aggression and even violent suicide.
Some drugs are thought to alter serotonin levels and thus
increase aggressive behaviour. Man et al (1990) gave 35
healthy subjects dexfenfluramine, which is known to deplete
serotonin. Using a questionnaire to assess hostility and
aggression levels, they found that dexfenfluramine treatment
in males (but not females) was associated with an increase in
hostility and aggression. This demonstrates a clear link
between lower levels of serotonin and aggressive behaviour.
Dopamine
There is some evidence that a link between high levels of
dopamine and aggressive behaviour exists. Lavine (1997)
claims that increases in dopamine activity via the use of
amphetamines have also been associated with increases in
aggressive behaviour. Antipsychotics which reduce dopamine
activity in the brain have been shown to reduce aggressive
behaviour in violent delinquents (Buitelaar, 2003). This
demonstrates a clear link between higher levels of dopamine
and aggressive behaviour.
Hormonal AO1
Testosterone
The male sex hormone testosterone is thought to influence
aggression from young adulthood onwards due to its action
on brain areas involved in controlling aggression. Dabbs et al
(1987) measured salivary testosterone in violent and nonviolent criminals. Those with the highest testosterone levels
had a history of primarily violent crime whereas those with
lowest levels had committed only non-violent crimes.
Students of non-prison population have found similar trends.
Lindman (1987) found that young males who behaved
aggressively when drunk had higher testosterone levels than
those who did not act aggressively.
LT3 - Neural and Hormonal Mechanisms in Aggression
Commentary/Supportive Evidence (AO2)
(3/4 pieces for 24 mark question)
 Evidence from non-human studies
One strength of research into the link between lower levels of serotonin and aggressive behaviour is that supportive
evidence comes from non-human studies.
Raleigh et al (1991) conducted a study on vervet monkeys. They found that individuals fed on experimental diets
high in tryptophan (which increases serotonin levels) exhibited decreased levels of aggression. Individuals fed on
diets that were low in tryptophan exhibited increased aggressive behaviour.
This is a strength because it suggests that the difference in aggression could be attributed to serotonin levels.
As a consequence this increases the credibility of the research into the link between serotonin and aggressive
behaviour.
 Evidence from Antidepressants
A further strength of the research into the link between serotonin and aggression is that supportive evidence comes
from research using antidepressants.
Bond (2005) established that low levels of serotonin are associated with low impulse control and aggressive
behaviour. Drugs that clinically raise serotonin levels (SSRIs) produce a concurrent lowering in aggression.
This is a strength because it further establishes a link between lowered levels of serotonin and aggression indicating
that this neurotransmitter (or lack of) plays a vital role in displays of aggressive behaviour.
As a consequence, the credibility of the research into the link between serotonin and aggression is strengthened.
MAID (A03)
(At least one AID paragraph in each essay)
Reductionism vs Holism
One issue with the research into neural and
hormonal mechanisms of aggression is that it is
reductionist.
This is because it reduces the complex behaviour of
aggression down to simple neurotransmitter and
hormonal imbalances in the brain.
Whilst this allows for aggression to be studied in
great detail, it does not consider other factors that
may contribute to aggressive behaviour in humans.
For example the complexity of human social
behaviour is ignored. The processes of social
learning theory and deindividuation have been
shown to have an impact on aggressive behaviour.
This casts doubt on the explanatory power of
neural and hormonal mechanisms in its attempt to
explain aggression. In order to truly understand this
complex behaviour, the individual as a whole must
be taken into account.
 Meta-analysis
One issue with the research into the effect of dopamine on aggression is that the link between this neurotransmitter
and aggressive behaviour is still unclear.
Scerbo and Raine (1993) carried out a meta-analysis into neurotransmitter levels in antisocial children and adults.
They reported a consistent link between lower levels of serotonin and aggression. However they found no
significant rise or fall in levels of dopamine.
Whilst this provides strong empirical support for the link between serotonin and aggression, it suggests that the role
of dopamine in aggression may be more complex.
As a consequence this reduces the credibility of the claim that dopamine levels have an impact on aggression.
 Inconsistent Evidence
One weakness of research into the link between testosterone levels and aggression is that there are several issues
with the supporting evidence.
Albert et al (1993) argued that the research into this link is largely unreliable. In addition most studies showing
positive correlations have involved small samples of men within prisons, using either self-report measures of
aggression or judgements based solely on the crimes committed.
This carries with it a wealth of issues such as population validity (only using male prisoners), social desirability (lying
on their questionnaires) or lack of control over extraneous variables (not considering the circumstances in which the
crimes were committed).
L: As a consequence this casts doubt over the credibility of the research into the link between testosterone and
aggression.
Gender Bias:
One issue with the research into the link between
testosterone and aggression is that it is gender bias.
For example most studies have involved only male
participants, failing to investigate the effect
testosterone has on females.
A small area of research by Archer (2005) into this
has established that the association between
testosterone and aggression is actually higher for
female than male samples.
This lends credibility to the assumption that
increased testosterone does in fact lead to
aggression.
However it reduces the explanatory power of the
original research since it fails to consider the effect
of testosterone on aggression in females.