Homicidal men with antisocial personality disorder exhibit significantly more neurological "soft signs" than typical males, according to a recent study.
Neurological soft signs (NSS) are minor anomalies not attributable to specific brain damage, such as an abnormal blink reflex or difficulty in discriminating between blunt and sharp objects by touch. A high NSS score suggests the presence of a central nervous system defect caused by either genetic anomalies or environmental insults such as prenatal or perinatal trauma. High NSS scores are associated with an elevated risk for significant psychological problems.
In the current study, Nina Lindberg and colleagues compared 14 homicidal men, all diagnosed with antisocial personality disorder and referred for forensic psychiatric evaluation, to 10 healthy men and eight patients with schizophrenia. (Schizophrenics typically have elevated NSS scores.) None of the patients had overt brain abnormalities or a history of neurological disease.
The researchers report, "The NSS scores of antisocial offenders were significantly increased compared with those of the healthy controls, whereas no significant differences were observed between the scores of offenders and those of patients with schizophrenia." While all of the homicidal men were intoxicated when they committed their crimes, they were alcohol-free at the time of evaluation, and their results were not affected by alcohol withdrawal or detoxification.
Lindberg et al. say their findings are consistent with mounting evidence showing a link between aggressive behavior and brain dysfunction. They cite a similar study of children showing a correlation between NSS and both oppositional defiant disorder and conduct disorder, and a study which found an elevated prevalence of NSS in adult sociopaths. Adolescent boys with repetitive aggression also have been reported to display more abnormal "mirror movements," a neurological soft sign, than non- aggressive controls.
The researchers conclude, "It can be speculated that neurological soft signs indicate a nonspecific vulnerability factor in several psychiatric syndromes, which are further influenced by a variety of genetic and environmental components. One of these syndromes may be antisocial personality disorder with severe aggression."
"Neurological soft signs in homicidal men with antisocial personality disorder," Nina Lindberg, Pekka Tani, Jan-Henry Stenberg, Björn Appelberg, Tarja Porkka-Heiskanen, and Matti Virkkunen, European Psychiatry, Vol. 19, No. 7, November 2004, 433-37. Address: Nina Lindberg, Department of Physiology, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, P.O. Box 63, Helsinki 00014, Finland.