The most significant relationships have been found between violent behavior and the neurotransmitter system (Burrowes 1988.)
More information on neurons and neurotransmitters
Any brain activity can be considered the result of an integration between excitatory and inhibitory components, and abnormal aggression in particular may depend on a defective balance between the brain's excitatory and inhibitory mechanisms. Genetic predisposition and induced or acquired alterations of these mechanisms work to concur strong aggression.
Relationships suggested between these mechanisms and aggression include the excitatory neurotransmitters acetylcholine and norepinephrine, and the inhibitory neurotransmitters serotonin and GABA.
It can be assumed that decreased inhibitory neurotransmission necessarily corresponds to uncontrolled activation, or disinhibition, of brain fuctions (Valzelli 1982,) as since most neurons are firing almost continuously, the brain can be considered a "synaptic bomb" (Valzelli 1984) that would explode in epileptic convulsions in the absence of inhibitory devices. Serotonin and gamma-aminobutyric acid (GABA) play this inhibitory role together.
The most meaningful relationship has been reported as an inverse association between the inhibitory neurotransmitter serotonin and aggressive behavior in humans. A range of studies have demonstrated that reduced amounts of central nervous system serotonin metabolites are associated with such behavior (Burrowes 1988.) The earliest evidence for this comes from the finding of low 5-HIAA (a serotonin metabolite) levels in patients who attempted particularly violent suicides (Burrowes 1988) (suicide can be viewed as a form of self-aggression,) and has been reproduced many times since.
Serotonin pathways lead to brain areas, such as the limbic system, involved in the production of emotional-affective behavior, including aggression, regulating their activity and the resulting behavior. It is possible to see, therefore, why aggression is a result of low serotonin because the levels are too low to stop the limbic system from being activated!
The synthesis and level of serotonin in the brain are regulated by the availability of the precursor amino acid tryptophan. In an experiment by Gibbons, male rats which were kept on a tryptophan-free diet for four to six days had a 26 percent decrease in serotonin levels and showed an increase in mice killing (Nutrition Reviews 1981.)
What foods have been correlated with murder? Click here to see! What you should not overconsume... Lesions in the areas of the brain that produce serotonin can also lower levels for obvious reasons.
These findings suggest that serotonergic transmission may be impaired in some violent offenders, either genetically predetermined or chemically or dietarily induced, a defect that may serve to reduce impulse control.
Although the bulk of evidence seems to indicate a direct correlation between neurotransmitters and aggression, to strictly associate violent behavior with brain chemicals is an oversimplification that does not take into account the many other factors that affect this behavior. What can all this information do for us? Click here to find out! Possible Interventions
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