AGGRESSION – NEURAL MECHANISMS IN AGGRESSION
THE LIMBIC SYSTEM HYPOTHALAMUS SEROTONIN HYPOTHALAMUS SUPPORT
The limbic system is a primitive area Despite its small size, the Serotonin is a neurotransmitter, and in Support for the hypothalamus has been
where violent impulses can arise. hypothalamus plays a pivotal role in an found in animal research.
normal levels exerts a calming,
astounding number of functional and inhibitory effect on neuronal firing of A researcher found that stimulating the
It is a collection of structures (including behavioural activities that are essential the brain lateral area of the hypothalamus in cats led
the hippocampus, hypothalamus and
for day to day survival of the individual to predatory aggression, hunting
amygdala) which play a central role in Serotonin typically inhibits the firing of behaviour. It was also found that rage
animal (or person) and for continuing
regulating emotional behaviour aggression was elicited by stimulation of
survival of its species. the amygdala.
including aggression the medial hypothalamus; this involves
PREFRONTAL CORTEX Low levels of serotonin (particularly in arching of the back, teeth baring and
AMYGDALA
the prefrontal cortex) remove this hissing. This suggests that different types
A region which governs ‘higher order’ of aggression are controlled by different
Has a key role in how humans assess functioning including planning and inhibitory effect with the individual less
environmental threats and challenges. brain areas.
decision making This area helps to able to control impulsive and
It is part of the brain that controls fear, regulate impulses and may help to aggressive behaviour Nevertheless, in humans it is likely that
anger and other emotional responses. inhibit aggressive behaviour Low higher brain areas also play a part in
It perceives threats and triggers ANS activity of this area means you aren’t aggression, since human aggression
flight/flight response. receiving high order functioning appears to be linked to social behaviour
and cognition. X animal studies
PREFRONTAL CORTEX RESEARCH AMYGDALA RESEARCH Responders’ brains were scanned by FMRI. was used to assess hostility and aggression
It was found that when responders levels and found that among males hostility
A researcher provided evidence for In humans, an amygdalectomy reduces and aggression levels increased after
rejected unfair offers (aggressive reaction
aggression being the result of a aggression in previously violent individuals; treatment of the drug. However, the
to social provocation) scans revealed a fast
malfunctioning prefrontal cortex. PET scans however, a side effect of this is the loss of methodology can be criticised for collecting
emotion, initiative and enthusiasm. It is and heightened response by the amygdala.
of 41 convicted murderers showed data using self-report rather than a more
abnormally low levels of activity in the therefore possible that the amygdala They also found taking a benzodiazepine scientific measure. It is difficult to collect
doesn’t directly cause aggression, but is reliable and valid data on the effect of
prefrontal cortex, compares to normal drug before halved the number of
involved in processing associated serotonin on aggressive behaviour using
individuals, suggesting reduced impulsive rejections and decreased the activity of the
emotions, such as anger. This means cause questionnaires.
control. The researcher states that and effect between the amygdala and amygdala. Therefore, showing a strong
influences on brain development including aggression is difficult to establish. association between reactive aggression Support for this explanation comes from
neglect, poor nutrition and maternal and amygdala activity. experiments on vervet monkeys fed diets
smoking inhibit normal development of However, research provides strong high in tryptophan (which decreases
evidence for the role of the amygdala. SEROTONIN RESEARCH
neural connections in the prefrontal cortex, serotonin levels in the brain). These
and since the brain is shaped by the Aggressive behaviour was measured using monkeys exhibited decreased aggressive
Research supports low levels of serotonin
the ‘Ultimate game’ involving two players. behaviour. Those fed diets low in
environment, the root cause of aggression in aggressive behaviour; a drug
The proposer offers to split the money in a tryptophan displayed increased aggression.
may be environmental rather than dexfenfluramine was administered to 35
certain way with the responder. If the This evidence would suggest that serotonin
biological. RLA – brain scans in court cases, responder accepts it is split as proposed; if healthy adults. This drug is known to
murder was beyond the murderer’s control is involved in aggressive behaviour.
they reject they both receive nothing. deplete serotonin levels. A questionnaire
,
AGGRESSION – HORMONAL MECHANISMS IN AGGRESSION: TESTOSTERONE
TESTOSTERONE YOUNG BOYS ORBITOFRONTAL CORTEX
Testosterone is a steroid hormone The elevated levels of testosterone in Testosterone is thought to have an
from the androgen group and is found young boys from the start of puberty effect on the orbitofrontal cortex.
in mammals, reptiles, birds and other may explain why young males tend to
If the individual has high levels of
vertebrates. exhibit the most aggressive behaviour,
testosterone then the activity of the
which declines with age.
Research suggests that there is a link OFC is reduced, which means that in an
between testosterone and aggressive emotional situation, there could be a
behaviour. heightened aggressive response, due to
poorer reasoning and impulse control.
SUPPORTING EVIDENCE ANIMAL RESEARCH META ANALYSIS OTHER FACTORS
Evidence for high levels of testosterone A researcher demonstrated that castrated A researcher conducted a meta- SLT suggests that aggression is learnt
increasing aggression in humans has been animals have decreased aggression, and analysis of 45 studies and found a via modelling: observation and
found. A researcher took saliva samples then if testosterone is replaced through mean correlation of only 0.14 between
from 692 young male prison inmates and therapy the pre-castration levels of imitation of other people’s aggressive
testosterone and aggression. This behaviour.
found that high testosterone levels were aggression come back. This demonstrates
associated with more violent crimes, parole experimentally that aggression is causes by
would suggest only a minor
board decisions against release, and more testosterone. relationship between testosterone and Explanation can be considered
prison rule violations. Even in women, it aggression. reductionist as it is suggesting that
was found high testosterone levels were Animal research is useful in providing aggression is due to just one single
insights into the effect of testosterone on Cause and effect therefore cannot be
related to crimes of unprovoked violence hormone.
and increased numbers of prior charges. aggression, which could not ethically or established, and many other factors
practically be conducted on humans. must play a role in aggression, other
Use of saliva is a very reliable method. Yet However, research into animals is the correlation would be greater.
his sample of prison inmates makes it very problematic because of the differences
difficult to apply the findings of between human and animals aggression. Other research casts further doubts,
testosterone on aggression to other Human aggression has many different suggesting that aggressive behaviour
sections of the population and is therefore factors, cognitions and emotions elevates levels of testosterone and not
limited and lacking in population validity. experienced are far more complex.
the other way around.
