Neurotransmitters are chemicals in the brain. Serotonin is a
neurotransmitter which has been linked to aggression by inhibiting responses to
stimuli which can lead to aggressive responses. Low levels of serotonin have
been associated with increased aggression.
Mann et
al (1990) did a study to support this by giving 35 healthy male participants a
drug which decreases the levels of serotonin in the brain. They then filled out
a questionnaire on hostility and aggression and it was found that aggression
levels had increased since the drug treatment. This supports the fact that
serotonin is linked to aggression as when the participants had lower levels of
serotonin than usual their aggression level was higher in all participants
which suggested that the serotonin change was the reason for higher aggression
levels and not an extraneous variable.
Mann’s
study used a self-report method of gaining information from the participants.
This reduces the validity of the study as participants could have given answers
which they thought were socially desirable or what Mann wanted to hear and not
truthful ones which means the conclusions Mann drew form the study could be
based on invalid evidence.
Raleigh
et al (1991) also conducted a supporting study into serotonin as a factor of
aggression where he found that when monkeys were fed on a diet high in
tryptophan, which increases levels of serotonin, their aggression levels
dropped compared to that of monkeys fed a diet not high in tryptophan. This
supports serotonin as a factor in aggression as a change in serotonin levels in
the monkeys changed their aggression levels.
Raleigh’s
study however is lacking in external validity because it was carried out on
animals. It cannot be fully generalized to humans as it cannot be proved that
we have the same psychological makeup and therefore our brains may not work in
the same way as theirs. This is a big weakness in animal studies and means that
this study is not as supporting of serotonin as a factor of aggression as
studies that have been carried out on humans.
Another
neurotransmitter which is said to affect aggression is dopamine and high levels
of this have been linked to high levels of aggression. There has however no
conclusive evidence to show a causal role of dopamine in aggression, research
suggests it may be a consequence instead. Couppis and Kennedy (2008) did a
study which supported dopamine as more a consequence than a causal factor of
aggression by finding that in mice, a reward pathway in the brain becomes
engaged in response to aggression and that dopamine is a positive reinforce in
this pathway. This suggests that it may be involved in aggression in some way
however not actually be a factor for it. This study has the same problems with
external validity as Raleigh’s study as it was carried out on mice not humans.
Testosterone
is a male sex hormone which is thought to influence aggression due to its
action in the areas of the brain which are involved in controlling
aggression. Archer (1991) did a
supporting study where he analysed 230 males over five studies and found a
positive correlation between aggression and testosterone levels. This would
show that testosterone was a factor involved in aggression however as it was a
correlational study it can show a relationship between the two but not a
causation which means that this study cannot show that testosterone is a cause
of aggression.
Dabbs
et al (1987) also did a study to support testosterone as a factor of aggression
by measuring salivary testosterone levels in violent and nonviolent criminals.
He found that those with the highest testosterone levels had a predominantly
violent and aggressive history whereas those with the lowest had committed only
nonviolent crimes. He found similar results when doing the same experiment on
non-criminal communities. This supports testosterone as a factor for aggression
as the most aggressive people were found to have the most testosterone across
many communities which suggests that it is testosterone having this effect and
not another extraneous variable.
Most studies concerning testosterone and aggression have a huge gender bias. As
testosterone is a male sex hormone the majority of studies into the effects of
testosterone on aggression are carried out solely on males which means that the
results cannot be generalized to females.
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