Neural Mechanisms in Aggression

Their meta-analysis examined neurotransmitter levels in antisocial children and adults. They consistently found lower levels of serotonin in individuals described as being aggressive, but found no significant rise or fall in dopamine levels.

Indications of reduced levels of serotonin were found in all antisocial groups, but were particularly marked in those individuals who had attempted suicide.

This suggests that serotonin depletion leads to impulsive behaviour, which in turn may lead to aggressive behaviour in various forms.

Neurotransmitters are chemicals that enable impulses within the brain to be transmitted from one area of the brain to another.

Low levels of serotonin and high levels of dopamine.

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

Low levels of serotonin in the brain have been associated with an increased susceptibility to impulsive behaviour, aggression and even violent suicide.

Mann et al gave 35 healthy subjects dexfenfluramine, which is known to deplete serotonin. Using a questionnaire to assess hostility and aggression levels, they found that dexflenfluramine treatment in males (but not females) was associated with an increase in hostility and aggression scores.

It is not as well established as the serotonin link but there is evidence to suggest that a link exists.

Lavine found that increases in dopamine activity via the use of amphetamines have been associated with increases in aggressive behaviour.

Buitelaar found that antipsychotics, which reduce dopamine activity in the brain, have been shown to reduce aggressive behaviour in violent delinquents.

In a study of vervet monkeys, they found that individuals fed on experimental diets high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression and vice versa.

Popova et al: in animals that are selectively bred for domestication and for increasingly docile temperaments, there is a corresponding increase, over generations, in brain concentrations of serotonin.

Bond established that drugs used to clinically raise serotonin levels have produced a lowering of aggressive behaviour. Bond found this in clinical studies of antidepressant drugs that elevate serotonin levels.

She established that such drugs do tend to reduce irritability and impulsive aggression.

Couppis and Kennedy found that in mice, a reward pathway in the brain becomes engaged in respond to an aggressive event and that dopamine is involved as a positive reinforcer in this pathway. This suggests that individuals will intentionally seek out an aggressive encounter solely because they expeience a rewarding sensation from it.

The links between biological mechanisms and aggression are well established in non-human animals. However, the position is not wuite so clear in the case of humans. This is not to deny that such links exist, but rather that the complexity of human social behaviour means that a biological explanation for human aggression is insufficient on its own to explain all the many different aspects of aggressive and violent behaviour.