neural and hormonal mechanisms

• What is the limbic system

  A central area of the brain that regulates emotional urges.
• Limbic system and aggression

  Firstly, the hippocampus is involved in the formation of long-term memories which allows animals/humans to compare a current threat with similar past experiences. For example, if an animal who has previously been attacked encounters that or a similar animal again, they may be more likely to respond in a fearful or aggressive manner. Impaired hippocampus function also prevents the nervous system from putting things into meaningful context and may lead to amygdala to respond to sensory stimuli with aggression.

  Secondly, the most important structure linked to aggression by far is the amygdala whose role is to process emotion. If the amygdala in humans malfunctions due to a tumour, damage or atypical development, then this can lead to raised levels of testosterone, making aggression more likely.

  Finally, the hypothalamus is responsible for the regulation of the autonomic nervous system, which in turn regulates responses to emotional circumstances. Therefore, damage to this area can result in an inappropriate aggressive response to a perceived threat.
• Strength of limbic system as explaination

  Animal studies show that if certain areas of the amygdala are stimulated electrically, then the animal will respond aggressively by snarling.

  If these areas of the amygdala in animals are removed, then the animal will no longer respond in the same way. This provides evidence that the amygdala located in the limbic system may be responsible for aggressive behaviour.

  
  

  Sumer et al (2007) reported a case study of a 14-year-old girl who was showing aggressive, anger and rage. An MRI scan discovered a tumour in the limbic system and after the tumour was treated with drugs, the patient's levels of aggression returned within "normal" levels. This suggests that tumours in the limbic system could be the cause of aggressive behaviour.
• Frustration-aggression theory - Limitation

  An alternative explanation that provide a better understanding of human is aggression is provided by Frustration aggression theory. According to Dollard, frustration leads to aggression. This hypothesis is based on the psychodynamic concept of catharsis and views aggression as a psychological drive similar to a biological one such as hunger. If our attempt to achieve a certain goal is blocked such as trying to get past in a busy pub, we experience frustration. This in turn leads to swearing or an aggressive drive such as a violent fantasy or violence.
• Deindividuation theory - Limitation (alternative theory)


  When we are part of a crowd, it is possible for us to lose our sense of identity and responsibility and in these circumstances, the social norms that usually keep us restrained with regards to antisocial behaviour are temporarily forgotten. We live for the moment, we stop monitoring and regulating our own behaviour and the result is antisocial/aggressive behaviour, for example crowd violence at football matches. This is a psychological explanation for aggression and therefore challenges the view that the limbic system is solely responsible for aggression.
• The role of serotonin

  Serotonin, which is a neurotransmitter, is thought to reduce aggression by inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response.

  Normal levels of serotonin in the orbitofrontal cortex are linked with a reduced firing of neurons, and is associated with greater self-control (less-likely to engage in aggressive behaviour).

  Low levels of serotonin have been linked with an increased susceptibility to impulsive behaviour, aggression and even violent suicide
• Strengths of serotonin

  Raleigh et al (1991) found that monkeys fed on a diet high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression and vice versa. This also demonstrates that low levels of serotonin are linked to higher levels of aggression suggesting that aggressive behaviour "may" be biologically determined.

  
  

  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. This supports the notion that impulsive aggression can be linked to neurotransmitters.
• Limitations of serotonin

  Biochemistry is a deterministic explanation for aggression, removing the notion of free will and choice over our aggressive responses and instead laying the blame with neurochemistry in the brain.

  
  

  Alternative explanation- e.g. SLT
• The role of testosterone

  Testosterone is a male hormone produced mainly in the testes and is associated with sexual and aggressive behaviour. Males are generally more aggressive than females and at the age where testosterone levels are at their highest (21-35) there is an increase in male to male aggression. Attention has therefore focused on the male sex hormone testosterone, an androgen responsible for the development of masculine features. It may be that changes in testosterone influence aggression by increasing amygdala activity.
• Wagner - AO3 strength

  Observed reduced levels of aggression in mice after they were castrated (reducing testosterone). Furthermore, the mice returned to normal levels of aggression after they were supplemented with testosterone injections. This supports the research that testosterone and aggression are linked.

  However, animal study...