Neural Mechanisms

• The limbic system is the network of subcortical structures in the brain (including the hypothalamus and the amygdala) thought to be closely involved in regulating emotional behaviours such as aggression.
• Papez (1937) made the first attempt to link the limbic system to emotional behaviours such as aggression.
• This was later revised by Maclean (1952).

The limbic system is comprised of:

• The cingulate gyrus.
• Septal area.
• Hypothalamus.
• Fornix.
• Amygdala.
• And parts of the hippocampus and thalamus.

• The most important of these structures (in the limbic system) is the amygdala.
• This determines how both humans and non-human animals behave in response to environmental threats and challenges.
• The reactivity of the amygdala is proven to be an important predictor of aggressive behaviour.

• Gospic et al. (2011) used a well-established laboratory method of assessing aggressive behaviour called the Ultimatum Game that featured two players.
• In the Ultimatum Game, the proposer offers to split money in a certain way with the responder. If the responder accepts, the money is split as proposed. But if the responder rejects the offer, both receive nothing.

• Participants in this study played as responders while having their brain scanned by fMRI, which highlights activity in different areas of the brain.
• The researchers reported that when responders rejected unfair offers the scans revealed a fast and heightened response by the amygdala.

• Gospic et al. also found that if a benzodiazepine drug (which reduces arousal of the autonomic nervous system) was taken before the game it had two effects on responses to unfair offers:
  • It halved the number of rejections, that is, it reduced aggression.
  • It decreased the activity of the amygdala.
• This suggests an association between reactive (impulsive) aggression and amygdala activity.

• Recent studies indicate that the amygdala does not operate in isolation in determining aggression but appears to function in tandem with the orbitofrontal cortex (OFC), which is not part of the limbic system.
• The OFC is thought to be involved in self-control, impulse regulation and inhibition of aggressive behaviour.

• Coccaro et al. (2007) found that patients with psychiatric disorders that feature aggression had reduced activity in the OFC.
• This has been found to disrupt impulse control function and consequentially lead to increased aggression.

• Combined with findings from Gospic et al. (2011), this indicates that the regulation of aggression is highly complex and involves at least three structures in the brain:
  • The amygdala.
  • The OFC.
  • The connection between the two.