How can neurotransmitter and hormonal imbalances be associated with increased criminality?

In the field of criminology, biological theories suggest that certain biochemical factors may increase the likelihood of criminal behavior, though they do not serve as absolute determinants.1

Neurotransmitter Imbalances

Research indicates that specific neurotransmitter levels in the brain are linked to behavioral modulation. Notably, low levels of serotonin have been associated with increased criminality. In vertebrates, high levels of serotonin are generally linked to reduced aggressiveness, while high levels of norepinephrine are associated with increased aggressiveness.12

Hormonal Imbalances

Hormonal fluctuations, particularly involving testosterone, are also correlated with aggressive tendencies. Higher levels of circulating testosterone are often linked to increased aggression, a relationship observed across many vertebrate species. However, this connection is complex and multidirectional; while hormones can influence behavior, participating in conflict can also rapidly alter an individual's hormone secretion, such as increasing testosterone in winners or elevating cortisol in those who lose.13

Because these biological factors are often influenced by environmental conditions, the direction of causation remains unclear, and most individuals with these imbalances do not engage in criminal activity.1