Neural & Hormonal factors in aggression

• Brain has 2 structures (neural mechanisms) involved in onset of aggression:

  1. 'Devil'= initiates aggression: Amygdala & Hippocampus
  2. 'Angel'= suppresses aggression: Prefrontal Cortex
• • Amygdala & Hippocampus= called the limbic system.
  • This area of the brain helps coordinate behaviours aimed at satisfying emotional & motivational urges such as aggression, anger, fear etc.
• The Amygdala: analyses incoming sensory information for emotional importance & coordinates an appropriate response.
• The Hippocampus: coordinates the emotional responses of the Amygdala to the long term memory, also allows for the formation of emotional long term memories.
• Evidence for the Amygdala:

  • Pardini et al carried out a longitudinal study of 56 males from childhood to adulthood.
  • Some PPs had an MRI scan at age 26.
  • Results showed that PPs with a smaller Amygdala were more aggressive & violent, and that this was true even when confounding variables were controlled.
  • Suggests that having a smaller Amygdala compromises ability to respond appropriately & makes aggression more likely.
• The Prefrontal Cortex: a rational part of the brain which helps suppress aggression.
• Evidence for the Prefrontal Cortex:

  • Phineas Gage following an accident where a metal rod damaged his pre-frontal cortex, became unlike his usual self; he became rude, used profanities when he didn't before, & became more impulsive & aggressive.
  • Shows that a role of the Prefrontal Cortex is to suppress elements of aggression.
  • Shows that the frontal lobe has important functions in impulse control to reduce aggressive outbursts.
• Brain/ neurochemistry (neural mechanisms):

  • Serotonin has an inhibitory function when it comes to aggression, ie higher levels= less aggression, low levels= more aggression.
  • This is because it generally inhibits neuron firing of the Amygdala- a part of the brain responsible for emotions such as fear & anger.
  • Serotonin Deficiency Hypothesis refers to how less serotonin may lead to reduced ability to control aggression & impulsivity in general.
  • Serotonin has effects all over the body; low levels in the brain can cause impulsive behaviour, aggression, overeating, depression, alcohol abuse & violent suicide.
• Research for brain/neurochemistry:

  • Raleigh at al fed Vervet monkeys a diet high in tryptophan (type of pure carbohydrate used in production of serotonin).
  • Showed they had reduced aggressive responses when compared to a low tryptophan diet.
  • Weakness: non-human animals used.
  • Weakness: lacks empiricism (being directly observed)- serotonin hasn't been measured.
• Hormonal mechanisms:

  • Testosterone (male sex hormone producing male characteristics) is thought to be linked to aggression due to its activation of brain areas, such as the Amygdala, involved in the control of aggression.
  • The more testosterone a person has, the harder they find it to control themselves & are therefore more prone to aggressive acts.
  • Males are more aggressive than females & have more testosterone.
  • Males are most aggressive at an age where testosterone levels are highest.
• Evidence for Testosterone:

  • Wagner et al found that castrating male mice decreases aggressive behaviour, but if you inject testosterone, the aggression comes back (biting).
  • However, the use of non-human animals is a weakness.
• Evidence for Testosterone:

  • Harisson et al gave testosterone to 56 men (aged 20-50) then let them play a frustrating computer game.
  • Found aggressive responses increased when testosterone was received, although this was not the case for all.