A study of violent and sexual offenders shows an apparent link between psychopathic behavior and brain levels of metabolites of serotonin and dopamine, according to an article in the June issue of the Journal of Neurology Neurosurgery and Psychiatry.

The findings are based on evaluation of 28 Swedish men up to 45 years of age, all of whom had committed violent crimes, including murder, attempted murder, aggravated assault, arson, rape, or sexual assault of children.

Samples of cerebrospinal fluid were obtained from each patient and tested for levels of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA). The first compound is a metabolite of serotonin and homovanillic acid is a metabolite of dopamine. Research indicates that serotonin regulates brain levels of dopamine, and it is dopamine that influences aggressive impulses.

The men were scored against a checklist for psychopathic personality traits and carefully assessed for evidence of disruptive childhood behaviors such as attention deficit hyperactivity disorder and conduct disorder.

The results showed that higher levels of homovanillic acid (the dopamine metabolite) and lower levels of 5-hydroxyindoleacetic acid (the serotonin metabolite) were significantly associated with psychopathic traits, especially behaviors, in this group of men.

The ratio of the 2 metabolites was also strongly linked to a history of childhood disruptive behaviors, and the authors hypothesize that a combination of attention deficit hyperactivity disorder and conduct disorder might be a behavioral precursor to adult psychopathic behavior.

The results confirm those of a previous recent study of 22 violent men, conducted by the same research group. Future research may provide more insight into the apparent link between relative amounts of neurotransmitters and psychopathic manifestations.