Neural and hormonal mechanisms in aggression, including the roles of the limbic system, serotonin and testosterone.

Neural and Hormonal Mechanisms in Aggression

Description, AO1:

The Limbic System:

Subcortical structures in the brain (including the hypothalamus and amygdala) thought to be closely involved in regulating emotional behaviour.

How does the limbic system link to aggressive behaviour?

  • First attempt to link was made by Papez & later revised by McClean
  • Most important aspect of the system is the amygdala
  • The amygdala has a key role in how humans and non-humans assess and respond to environmental threats and challenges.
  • The reactivity of the amygdala in humans has proven to be an important predictor of aggressive behaviour.


Research showing a link between reactive aggression & the amygdala: Gospic et al (2011) use a lab method called the Ultimatum Game. 2 players – The proposer and the responder. The proposer offers to split the money in a certain way (fair or unfair) with the responder. If the responder accepts, the money is split as proposed. If the responder rejects the offer, both players receive nothing. The responders played while having their brain scanned using fMRI. Unfair offers (leading to an aggressive reaction from social provocation) = when responders rejected them there was found to be a fast and heightened response by the amygdala. In a variation participants were given an anti-anxiety drug (BZs) before the game, this had two effects; There was a reduction in rejected ‘unfair’ offers and a decrease of amygdala activity. This research can also be used as evaluation (AO3) in order to support the limbic system in aggressive behaviour.

Evaluation, AO3 of the Role of the Limbic System in Aggression:


(1) Point: Raine et al’s research supports the idea of a link between the limbic system and aggressive behaviour. Evidence: For example, Raine et al (1997) scanned the brains of 41 murderers and 41 controls. They found, using PET scans, that some had abnormalities in the way that their limbic systems functioned. Elaboration: This is a strength because it demonstrates that the limbic system could be implicated in aggressive behaviour, because if there wasn’t a link then there’d be no difference between the PET scan results of the murderers and controls.



(1) POINT: A weakness is that the research that links the limbic system to aggressive behaviour is correlational. EXAMPLE: For example, research suggests that abnormalities in the limbic system causes aggressive behaviour however, it could be that an increase in aggressive behaviour causes abnormalities in the limbic system. EVALUATION: This is a weakness because it means that a cause and effect relationship cannot be established between abnormalities in the limbic system and aggressive behaviour, therefore researchers cannot draw firm conclusions.


The Role of Serotonin in Aggressive Behaviour

Description, AO1:

What is serotonin?

A neurotransmitter involved in communication of impulses between neurons, it has a widespread inhibitory effect on the brain.

How does serotonin link to aggressive behaviour?

  • Normal levels of serotonin in the orbitofrontal cortex are linked to reduced firing or neurons, this is associated with a greater degree of behavioural self-control.
  • Decreased levels of serotonin may well disturb this mechanism, reducing self-control and leading to an increase in impulsive behaviour, including aggression.
  • Normal levels of serotonin means no aggressive behaviour.
  • Low levels of serotonin can lead to aggressive behaviour.


Research showing a link between impulsive behaviour and serotonin: Virkkunen et al (1994) compared levels of a serotonin breakdown product in violent impulsive and violent non-impulsive offenders. The levels were significantly lower in the impulsive offenders, and they also suffered from more sleep irregularities (serotonin regulates sleep patterns).

Evaluation, AO3 of the Role of Serotonin in Aggression:


(1) Point: Evidence to support the link between low serotonin levels and aggression comes from animal studies. Evidence: Raleigh et al (1991) found that vervet monkeys fed on a diet high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression and vice versa. Elaboration: This is a strength because it shows that low levels of serotonin are related to aggression, since the calmer monkeys had more of it, and the aggressive monkeys had less. This therefore suggests that aggressive behaviour is biologically determined.



(1) Point: A weakness of Raleigh’s research is that the study is carried out on animals. Example: For example, Raliegh uses ververt monkeys in order to investigate the link between serotonin and aggressive behaviour. Evaluation: This is a weakness because ververt monkeys and humans are biologically and physiological different, the biological changes in a monkey’s body that lead to aggression may not necessarily lead to aggression in humans. As a result, the findings from this research cannot be generalised/extrapolated.


The Role of Testosternone in Aggressive Behaviour

Description, AO1:

What is testosterone? An androgen (something that controls the development of male characteristics) produced in the male testes and in the adrenal cortex.

How does testosterone link to aggressive behaviour?

  • The ‘Basal model of testosterone’ suggests that testosterone causes a change in a person’s level of dominance.
  • The more testosterone that a person has, the more competitive and dominant they will become.
  • Therefore, it follows that a man with a high level of testosterone will take part in antisocial behaviour such as fighting.


Research showing a link between aggression and testosterone: Dabbs et al (1987) measured salivary testosterone levels in violent and non-violent criminals. Those with the highest levels of testosterone had a history of primarily violent crimes, whereas those with the lowest levels had committed only non-violent crimes. Studies of non-prison populations have found similar trends.


Evaluation, AO3 of the role of testosterone in aggression:


(1) Point: Evidence to support the link between low serotonin levels and aggression comes from animal studies. Evidence: Connor & Levine (1969) found that rats who had been castrated when they were young had lower levels of testosterone and also displayed lower levels of aggression. Elaboration: This is a strength because it supports a link between testosterone and aggression, the higher the level of testosterone, the more aggressive behaviour is demonstrated.