Limbic system

Gospic et al

Kramer

Coccaro

Raine

fMRI lab based games that provoked aggression

case study of 14 year old girl

showed orbital frontal cortex activity is reduced in psychiatric patients that feature aggression

This shows that aggression cannot be explained by the limbic system alone

Game features

Proposer officer

Responder

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suffered epileptic seizures since 3 years old

diagnosed with tumour in the limbic system

behaved aggressively expressing anger and rage

when tumour was treated with drugs she returned to normal levels of aggression

this suggests high levels of aggression may have been caused by the limbic system

Responder accepts=money is split

Responder rejects= Money is all lost

Rejection of an unfair offer

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respondents rejected unfair offer (or aggressive reaction) fast response by amygdala

scanned brains of 41 murdered and 41 controls

Abnormalities in limbic system functioned aggression

it is highly complex

HYPOTHALAMUS

Receives information from amygdala controls the release of hormones

including adrenaline

AMYGDALA

A malfunction in the amygdala coul dincrease testosterone levels

increase in testosterone = more aggression

HIPPOCAMPUS

involved in formation of long term memories and comparing conditions of past experiences

evaluates the emotional importance of the sensory information and prompts an apporopriate response

impaired function

prevents nervous system from putting things into relevant context

Serotonin

a neurotransmitter with inhibitory effects throughout the brain

Normal levels of serotnin are linked with reduced levels of firing neurons

involved with communication of impulses between neurons

associated with a greater degree of behavioural self control

decreased levels can lead to an increase in impulsive behaviour

low serotonin levels are thought to be linked to impulsive and aggressive behaviour

Bond

showed drugs that clinically raise serotonin levels such as anti depressants have found levels of irritability and impulsive agression

Virkunnen et al (1994) compared levels of serotonin metabolite in the cerebrospinal fluid in violent impulsive and non-impulsive offenders

found significantly lower levels in impulsive offenders

also found these offenders had disrupted sleep patterns

This supports role of serotonin in aggressive behaviour

Hormonal Mechanisms

Testosterone

a hormone from the androgen group that is responsible for the development of male features (masculine features)

plays a role in regulating social behaviour via its influence on certain areas of the brain

thought to influence activity in the Orbital Frontal Cortex (OFC)

when an individual has high testosterone it inhibits the activity of the OFC therefore in emotional situations - heighten emotional aggressive response is more likely

Higher levels of testosterone are linked with increased levels of aggression

Dabbs et al

found that those with high levels of testosterone had a history of primarily violent crimes

those with levels of testosterone primarily committed non-violent crimes

Dolan et al

found a positive correlation between testosterone level and aggressive behaviours in a sample of 60 male offenders in UK maximum security hospitals who had histories of impulsively violent behaviours

Weaknesses

Strengths

One strength is supporting evidence for the role of neural and hormonal mechanisms in aggression

Scerbo and Raine (1993)

carried out a meta-analysis of 29 studies

assessing levels of serotonin in anti-social children

found to have low levels of serotonin, resulting in a reduction in serotonin results in impulsive behaviour and aggression

Carre & Mehta's

dual hormone hypthosis claims high testosterone levels only lead to aggression when cortisol levels are low

This suggests that the combined activity of testosterone and cortisol may be a better predictor of aggression than testosterone

Too simplistic

Coccaro et al

Evidence on the role of testosterone is mixed

showed OFC activity is reduced in psychiactric patients that feature aggression

This shows that aggression cannot be explained by the limbic system alone - it is highly complex

Neural and hormonal mechanisms are issues with cause and effect

most research is correlational as alternatives are limited

because studies with humans would have ethical issues and animal studies raise issues with generalisability

as research is just correlational, it could be that carrying out aggressive acts results in changing of hormones and neurotransmitters