Neurotransmitters are chemicals that allow the brain to transmit signals from one part of the brain to another. Low levels of serotonin and high levels of dopamine have been associated with aggression. Serotonin is believed to reduce aggression by inhibiting emotional responses to stimuli that may have led to an aggressive response. Low levels of serotonin in the brain, particularly the pre-frontal cortex, have been linked with higher rates of impulsive behaviour and aggression, as the inhibiting effect is lessened.
High levels of dopamine are believe to cause aggression in individuals. This is seen in the use of anti-psychotics, used for patients suffering schizophrenia, to reduce dopamine levels. This has been found to then reduce aggressive behaviour shown by patients.
Testosterone is the male sex hormone and has consistently been linked to aggression. This is suggested to activate regions in the brain associated to an aggressive response. Cortisol has also been linked to aggression. It is suggested cortisol heightens the awareness we have of consequences of our actions therefore lower levels may lead to increased aggressive behaviour.
Mann et al found lower levels of serotonin were associated with high levels of aggression in males but not in females. This supports the theory that serotonin can play a mitigating tole role in aggressive behaviour as low levels were associated with increased aggression. A methodological issue is questionnaires were used to judge hostility scores therefore relied on the participants to self report. therefore participants may have shown demand characteristics and reported higher aggression, as that was the expected outcome of taking serotonin depleting drugs. Also social desirability may have affected results as individuals that valued aggression within their social group may have reported higher levels as they find it a desirable characteristic. Therefore the reliability and validity of results could be questioned therefore it is inconclusive as to the role serotonin has in aggression.
Raleigh et al found monkey fed on high serotonin diets exhibited less aggressive behaviour than those on low serotonin diets. Other studies have found that animals bred for domestication have had increased serotonin levels over each generation, proving further support for the role serotonin plays in aggression. However, issues occur within animal research as it could be argued to be morally wrong due to the injury inflicted. Also due to difference of anatomy results may not be generalisable to humans. Therefore such research studies can help conclude a link to hormones and aggression but we cannot determine the extent the findings would be reflected in humans.
Both Mann and Raleigh's studies provide support towards the serotonin link in aggression therefore overall can provide support that neural and hormonal factors likely influence aggressive tendencies. However, issues arise in research as most studies are based on correlational data therefore we cannot determine for certain cause and effect. Other unidentified factors may be responsible for the changes in levels of aggression and ascertaining the real cause for aggression is difficult, due to methodological problems in measuring aggression. Each study may operationalise the explanation differently making it difficult to draw firm conclusions.
Neural and hormonal explanations ignore the role of free will and environmental and social factors therefore suffer strong reductionism and determinism as it suggests neural and hormonal factors are the sole cause of our behaviour. The more accepted view is that they are one factor among a large number of factors which influences how we behave. Such views could cause stigmatising towards those with certain hormone imbalances raising socially sensitive issues as a result of research.
A neural and hormonal explanation cannot account for those with similar levels of e.g. serotonin or testosterone displaying different levels of aggression. However, the diathesis stress model offers explanation as to how biological and environmental factors may predispose an individual to act aggressively when triggered by a certain environmental factor. Therefore that may be a more accepted approach that a purely neural or hormonal one.
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