NEURAL + HORMONAL MECHANISMS

• LIMBIC SYSTEM 


   consisting of the amygdala, the hippocampus and the hypothalamus is associated with emotion and memory that affect aggression.
• AMYGDALA


  Stimulations of the amygdala can either increase or decrease aggression for example, malfunctions in the amygdala can raise levels of testosterone which increases aggression levels.
• AMYGDALA 


  GOSPIC ET AL =

  used brain scans (fMRI) with participants in a lab-based game that provoked aggression. Aggressive reactions were associated with a fast and heightened response by the amygdala
• HIPPOCAMPUS 


  stores long term memories and so is able to compare between current threats and past experiences. For example, impaired hippocampus function prevents the nervous system from putting things into relevant and meaningful context. This may cause the amygdala to respond inappropriately to sensory stimuli. 
• ORBITOFRONTAL CORTEX


  normal levels of serotonin exerts a calming, inhibitory effect on neural firing in the brain. Serotonin inhibits the firing of the amygdala, the part of the brain that controls fear, anger and other emotional responses. 

  Low levels = disturbs the mechanism, reduces self control and increases impulsive beh. including aggression
• TESTOSTERONE 


  is thought to influence aggression from adolescence. It is found in both sexes, but adult males produce about 10 times more than adult females. The highest level in males is between 15-25 years, which is also the most likely group to commit violent crimes. High levels of testosterone is reduced activity of the orbitofrontal cortex. It also reduces serotonin in the brain. 
• PROGESTERONE 


  levels vary in menstrual cycle (lowest during and just after menstruation) = low levels cause aggression.
• (+) LIMBIC SYSTEM 


  KLUVER AND BUCY =

  who removed parts of the limbic system from monkeys ie. the amygdala. The monkeys displayed lack of emotional reactions associated with fear and anger. Monkeys with removed parts lost the understanding of group hierarchies and would try to fight the more dominant members. This demonstrates the importance of the limbic systems in regulating aggressive behaviour. 
• (+) LIMBIC SYSTEM 


  PHINEAS GAGE =

  He experienced a brain trauma in which an iron rod was driven through his skull. Gage who was once a very kind, compassionate person post accident became very aggressive and hostile - friends stated he was ‘no longer gage’. This demonstrates that damage to the frontal lobe can later have an effect on sones personality making them more aggressive. 
• (-) LIMBIC SYSTEM 


  REDUCTIONIST + HOLISTIC =

  limbic system/amygdala does not operate in isolation in determining aggression & non-limbic structures are also involved. This is backed up by COCCARO ET AL finding OFC activity is reduced in those psychiatric disorders that feature aggression.  This reduced activity disrupts the OFC’s impulse-control function, which in turn causes aggression. This shows that the neural regulation of aggression is more complex than theories focussing on the amygdala.
• (+) SEROTONIN 


  POPOVA ET AL =

  found that animals that are selectively bred for domestication and docile temperaments have an increased serotonin level. This suggests that an increase in serotonin levels does in fact cause aggressive behaviour. 
• (-) SEROTONIN 


  HUBER ET AL =

  which suffers from the lack of validity. It was conducted on humans, but the measure of aggression was game playing, which could be said to lack the emotion involved in real life situations where aggression may occur. 
• (+) TESTOSTERONE 


  CONNOR + LEVINE =

  experimented on rats and found that those that had been castrated when they were young had lower levels of testosterone and also displayed low levels of aggression as adults. Even when injected with testosterone they would show passive behaviour. But those that were castrated after being fully developed and then given testosterone injections returned to pre-castration levels of aggression. This suggests that sensitivity to testosterone is part of the developmental process. 
• (-) TESTOSTERONE

  CARRE + MEHTA =

  developed a dual-hormone hypothesis.  They claim high levels of testosterone lead to aggression, but only when levels of cortisol (response to chronic stress) are low.  When cortisol is high, testosterone’s influence on aggression is blocked. - Gender differences.  Therefore the combined activity of testosterone and cortisol may be a better predictor of aggression than either hormone alone.