Behavioral neurobiology in forensic psychiatry: problems and prospects

Background In recent decades, considerable progress has been made in the study of the biological bases of violent behavior, so much so as to rekindle a heated debate on the notions of “free will” and “criminal responsibility”. These questions gained renewed prominence in Italy after the sentence of a criminal Court that decided to admit a “diminished responsibility defense” because the offender was found to be carrier of a few genetic variants that were thought to be associated with a predisposition to violence. Case report An adult female was charged with the murder of her sister. The first forensic psychiatric report excluded the presence of a mental disorder, so she was assessed responsible. A second forensic psychiatric evaluation took place, including: (1) psychometric assessment (MMPI-2 & PPI-R); (2) neuropsychological examination; (3) morphometric analysis with VBM and (4) genetic analysis of DNA aimed at identifying genetic polymorphisms associated with violence. The final report picked out the presence of a multiple personality disorder and of abnormalities in brain-imaging scans and in five genes that have been linked to violent behavior. The Court ruled a sentence of “diminished responsibility” arguing that the defendant's genes “would make her particularly reactive and vulnerable to aggressiveness in stressful situations”. Discussion A growing number of researches have investigated the relationship between biogenetics and violent behavior. In particular, recent studies have combined behavioral genetics and functional brain imaging with the rationale that specific polymorphisms may lead to brain changes which, in turn, may increase vulnerability to various forms of violent behavior. A critical next step in testing this ‘‘from genes to brain to violent behavior’’ hypothesis is to identify the role of the environment (epigenetics). Conclusion The use of neuroscience and behavioral genetics is increasingly considered potentially useful in providing objective data on the assessment of a defendant’s criminal competence. From a forensic psychiatric standpoint, nonetheless, it must be remembered that the necessary conditions whereby a mental disorder can take on the meaning of “insanity” should be that it has caused, in the specific case, such mental impairment as to compromise the capacity for cognition and/or volition and that it was causally linked with the crime.