Reduced amygdala and lateral orbitofrontal volumes in pre-trial murderers: The role of psychopathy

The orbitofrontal cortex and amygdala are two key brain areas frequently implicated in the etiology of violent and psychopathic behavior. This study examines whether structural abnormalities in these regions characterize homicidal offenders, and investigates the role of psychopathy in any such relationships. Structural MRI was conducted on 37 murderers referred for forensic examination and 50 community controls from China. Psychopathic personality was assessed by forensic psychiatrists using the PCL-R. The orbitofrontal cortex was segmented into medial and lateral regions, while surface-based anatomical modeling was used to identify deformations within the amygdala. Covariates included age, gender, total intracranial volume, schizophrenia, cognitive functioning, substance use, broken homes, and head injury. Murderers compared to controls had a smaller volume of the lateral, but not medial orbitofrontal cortex, in addition to smaller amygdala volumes, particularly in the left hemisphere. Deformations to the left amygdala in murderers were localized to the central, lateral, and basolateral nuclei. Murderers who planned their homicides showed a 14.3% reduction in the size of the amygdala. Within the murderer group, higher psychopathy scores were associated with reduced amygdala volumes, particularly with respect to affective features of psychopathy. Murderer-control differences could be attributed to higher levels of psychopathic personality in murderers. Sensitivity analyses confirmed findings. Findings implicate for the first time orbitofrontal and amygdala volume reductions in pre-trial murderers, and are suggestive of anomalies in emotional and moral decision-making, punishment sensitivity, and guilt in this group. • 37 Chinese Murderers and 50 Controls underwent anatomical MRI. • Murderers showed volume reductions in the amygdala and orbitofrontal cortex. • Findings particularly applied to those who planned their murder. • Higher psychopathy scores were associated with reduced amygdala volumes. • These are the first findings on structural brain deficits in pretrial murderers.