neural and hormonal influences

• The limbic system is an area of the brain that helps to coordinate behaviours that satisfy motivational and emotional urges, such as aggression. The 2 key structures in the limbic system is the amygdala and the hippocampus.
• The amygdala is responsible for quickly evaluating the emotional importance of sensory information and promoting an appropriate response. When certain areas are stimulated, an animal responds with aggression such as snarling. If the same areas are surgically removed, the animal no longer responds to stimuli that would have been previously led to rage. Researchers discovered that the destruction of the amygdala in a monkey dominant in the group, lead to the loss of the dominant place.
• The hippocampus is involved in the formation of long-term memories so it can compare current threats, with past situations. So if an animal has been attacked by another, the next time they see that animal, they will respond with either aggression or fear. Impaired hippocampi function prevents the nervous system to put things into context and so many not respond appropriately to sensory stimuli.
• Serotonin has a calming, inhibitory effect on neuronal firing in the brain. It inhibits the firing of the amygdala. Low levels remove this inhibitory effect so aggressive behaviour is less controllable. So, when the amygdala is stimulated by external events it gets active and aggression is more likely. Some drugs alter serotonin levels and so increase aggressive behaviour. Mann gave 35 pt dexfenfluramine (depletes serotonin). A questionnaire assessed hostility and aggression levels, they found this treatment in males was associated with an increase in hostility & aggression scores.
• Testosterone produces male characteristics, one of which is thought to be aggressive behaviour. Levels reach a peak in young males, then decline. Research was summarised by describing how removing the source of testosterone in different species typically resulted in much lower levels of aggression. Subsequently reinstating normal testosterone levels with injections of synthetic testosterone led to a return of aggressive behaviour.
• Men are seen as more aggressive than women and also have much higher levels of testosterone. In addition, at an age when testosterone concentrations are at their highest there is an increase of male-on-male aggressive behaviour. Dabbs measured salivary testosterone in violent and non-violent criminals. Violent crimes had higher levels.
• Pardini 2014 found that reduced amygdala volume can predict development of severe and persistent aggression.

  A longitudinal study of male participants from childhood to adulthood was done. Some of the 56 pt with varying histories of violence were subjected to a brain MRI at age 26. The results shows that pt with lower amygdala volumes exhibited higher levels of aggression and violence. The relationship between amygdala volume and aggressive behaviour remained even after other confounding variables were controlled.
• This research therefore demonstrates a hard determinist view.

  This could create a problem in relation to aggression, as if someone preforms an aggressive act, they could argue that they can’t be responsible for the actions as it is their neural or hormonal influences that made them act in an aggressive way.

  Maslow would also argue against a hard determinist view as he believes humans have free will and therefore, are responsible for all actions.

   
• There is support for the serotonin deficiency hyp for aggressive behaviour.

  A meta analysis of 175 studies, involving 6,500 pt was done. This found a small inverse relationship between serotonin levels and aggression. The magnitude of the relationship also varied with methods used to assess serotonin functioning and with self-reported versus other-reported aggression. Only other-reported aggression was positively correlated to serotonin functioning.

  This suggests that the relationship between serotonin and aggression is more complex.
• (Also, can use value of longitudinal studies.)

  (huge sample size and meta-analysis, however self-report method)
• In issue with the studies into hormonal influences is that there is inconsistent evidence.

  For example, positive correlations have been reported between levels of testosterone and self-reported levels of aggression among prison inmates. On the other hand, no correlation was found between testosterone levels and actual violent behaviour among male inmates in prisons.

  This suggests that the relationship between testosterone and aggression in humans remains clear.