Discuss the role of neural and/or hormonal mechanisms in aggression (8 marks+ 16 marks)

In normal levels serotonin can have a calming, inhibitory effect on neural firings in the brain. However, in low levels the inhibitory effect of serotonin is removed. This results in individuals being less able to control their impulsive and aggressive responses. Mann et al (1990) supports this theory. They administered the drug dexfenfluramine to 35 healthy adults. This drug is known to deplete serotonin levels in the brain. They then used questionnaires to assess hostility and aggression levels in the participants. They found that among males, but not females, hostility and aggression levels were increased after treatment with the drug. These findings suggest that low levels of serotonin are related to an increase in hostility and aggression. This study can be criticised because there may be an alternative explanation that aggression is not caused by low levels of serotonin in the brain but by low serotonin metabolism, which results in increased number of receptors. Serotonin receptor density has an inverse relation to serotonin levels in the brain, which can result in aggressive behaviour. Also, Mann et al (1996) found that among suicide ‘completers’ those with increased numbers of pre-frontal cortex serotonin receptors had chosen more violent methods of suicide, this disputes the theory as this suggests that an increased level of serotonin can lead to aggression not a low level.

Furthermore, Badawy (2006) suggested that the influence of serotonin on aggressive behaviour may be important in explaining the well-established relationship between alcohol and aggressive behaviour. It was found that alcohol consumption caused major disturbances in the metabolism of brain serotonin. Acute alcohol intake depleted serotonin level in normal individuals, whereas in susceptible individuals, this depletion may induce aggressive behaviour. These findings suggest that low levels of serotonin in susceptible individuals can result in increased aggression, supporting this theory.