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Biological explanations of
Neural & Hormonal Mechanisms…read more

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Aggression in humans is
associated with:
low levels of serotonin
high levels of dopamine.…read more

Slide 3

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· Thought to reduce aggression by inhibiting responses to emotional stimuli that might
other wise lead to an aggressive response.
· low levels , especially in the pre-frontal cortex have been associated with an
increased susceptibility to impulsive behaviour , aggression & even violent suicide.
· Support comes from the fact that the major waste product of Seretonin is low in the
cerebrospinal fluid of people who display aggressive behaviour.
Supporting Evidence
Mann (90) - Gave 35 healthy subjects dexfenfluramine , known to deplete Seretonin.
Using a questionnaire to asses hostility and aggression levels, found that
dexfenfluramine treatment in males was associated with an increase in hostility &
aggression scores.
Scerbo & Raine ­ correlational study - meta analysis of 29 studies which examined
neurotransmitter levels in anti-social children & adults , consistently finding lower
levels of Seretonin in aggressive individuals. But no significant rise or fall in dopamine
levels. Reduced Seretonin levels found in ALL anti-social groups , particularly in those
who attempted suicide. Supporting idea that Seretonin depletion leads to impulsive
behaviour which might be aggressive.…read more

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Research support on non-human animals
· Raleigh et al (91) ­ lab vervet Russia study ­ studied silver foxes
monkeys on experimental diet bred for reduced aggression, tamed by
high in tryptophan exhibited humans for over 30 yrs. found they
decreased levels of had higher levels of Seretonin than
aggression. Diets low in normally would be expected, with
tryptophan exhibited increased higher levels of tryptophan and lower
aggressive behaviour. levels of monoamine oxidase. Since
Suggesting difference in they were high in Seretonin & not
aggression could be aggressive , the claim low levels of
attributed to Seretonin Seretonin is associated with
levels. aggression is supported.
Mice ­ Where serotonin 1B (neurotransmitter acting on
central nervous system inducing behavioural changes) was
not functioning, found an increase in aggressive behaviour.…read more

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Evidence from drugs
· Bond (05) - Drugs that clinically raise Seretonin levels
should produce a concurrent lowering in aggression.
This happens in clinical studies of antidepressant drugs
that elevate Seretonin levels.
· Clinical trials ­ tryptophan on its own or combined with
Desyrel (serotonergic drug), has historically been given
to juvenile delinquents & unpredictable institutionalised
patients to reduce their aggressive tendencies.
· Alcohol - leads to aggression and produces major
disturbances in the metabolism of Seretonin. In a normal
individuals , alcohol intake reduces levels of serotonin.…read more

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· Summers et al (05)- globally acting serotonergic drugs do modify
aggressive behaviour but this cannot be singularly identified as
the only cause of activity in regions of the brain that could ultimately
have serotonergic effects on aggression .
· Study of negative relationship between serotonin & aggression is
based on correlational research, not allowing for cause & effect
relationships to be unequivocally established.
· Researchers have a duty to look after ppts but is all this research
ethically sound?
· How representative of humans are animal research studies?…read more

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