Neural and Hormonal Mechanisms in Aggression Flashcards Preview

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Limbic system

The LIMBIC SYSTEM is a network of brain structures linked to emotional responses such as fear and aggression.


The AMYGDALA is an important structure within the limbic system which allows organisms to respond to threats and challenges

and is a predictor of aggressive behaviour.


If areas of the amygdala are electrically stimulated in animals they will respond with aggression,

however, if the amygdala is removed they will no longer respond to stimuli which would have previously produced an aggressive response.



SEROTONIN is an inhibitory neurotransmitter which slows down neuronal activity in the brain


Normal levels of serotonin in the ORBITOFRONTAL CORTEX are linked with Behavioural self-control and producing a calming influence on behaviour.

However, DECREASED levels of serotonin leads to an increase in impulsive and aggressive behaviour.


it has been suggested that normal levels of serotonin within the orbitofrontal cortex

inhibits (i.e prevents) aggressive tendencies & has a calming influence on our behaviour.


This is because serotonin typically inhibits the firing of the amygdala

which is part of the limbic system that controls fear and aggression.


By having low levels of serotonin in the orbitofrontal cortex and the amygdala, any inhibitory effect with aggression is removed.

This means that these individuals are less able to control impulsive and aggressive behaviour.


• As a result of this, when the amygdala is stimulated by external factors such as an argument perhaps

it becomes more active causing the person to act on their instinctive impulses and become aggressive



Testosterone is a male sex hormone (androgen) required for the development of male reproductive organs. Testosterone also plays a role in regulating SOCIAL BEHAVIOUR because of its effects on areas of the brain.


on average, men produce between 4 and 10mg of the hormone per day and overall they have about 20 times more testosterone than women.

since males are typically the more aggressive sex, this could be due to higher testosterone


Levels of testosterone in males begin to peak around mid-puberty. The Home Office statistics reported in 2004 that “Violent incidents are most likely to involve male offenders between 16 to 24 years of age”.

the body is still developing up until 25 so this suggests that after testosterone has peaked, males will be less aggressive in adulthood

highest testosterone, most aggressive


Violent criminals in prison have higher salivary testosterone levels than non-violent criminals in prison (Dabbs et al 1987)

links testoterone to violence


Removing the source of testosterone in male animals (i.e. castration) reduces overall aggression levels (and is actually a recommended method by veterinary surgeons to “calm” aggressive pets). Reinstating testosterone with synthetic injections leads to an increase in testosterone (Sapolsky 1998)

reducing testosterone in males reduces aggression


There is supporting evidence for the limbic system being linked to aggressive behaviour

Participants were asked to play a laboratory game called the ‘Ultimatum Game’ and have their brains scanned by fMRI during play
The ‘proposer’ offered to split an amount of money with the ‘responder’ in a deal, but if the ‘responder’ rejected the offer, both received nothing.
Scans revealed there was fast and heightened responses in the amygdala when the ‘responders’ rejected unfair offers (an aggressive reaction to social provocation) (
increases validity that neural activity can cause aggressive behaviour


There is supporting evidence for the role of serotonin in aggression from experimental research

Participants were either given a drug which enhances serotonin called paraoxetine or a placebo and asked to play a laboratory based game where electric shocks were given and received in response to provocation. Participants in the paraoxetine condition gave fewer and less intense shocks compared to those in the placebo drug condition (when they had a previous history of aggressive behaviour)
increases val of low levels of serotonin causing


There is supporting evidence for the role of testosterone in aggression from violent offenders

Testosterone and aggression levels in 60 males with histories of impulsive and violent behaviour were measured in offenders in UK maximum security prisons. There was a positive correlation found between testosterone and aggression
Increases the validity of the role of testorone, showing linki between high levels and violence


There is contradictory evidence for the
relationship between testosterone and aggression

In correlational studies investigating actual recorded violent behaviour in male inmates, rather than self-reported aggressive feelings, there was no correlation between testosterones levels and actual violent behaviour
decreases the validity as it may just cause feelings of aggression not aggressive behaviour


There are methodological issues with research investigating
Neural and/or hormonal explanations of aggression

Most research investigating neural and hormonal influences on aggression is correlational. This means that cause (neural/hormonal) and effect (aggression) cannot be established. There are also likely to be significant environmental factors i.e. upbringing which could also contribute to aggression.
reduces the validity suggesting envrironmental contribution