The effects of neuroimaging and brain injury on insanity defenses

Although neurological evidence is used with increasing frequency in criminal trials, there is limited research examining the effects that this evidence has on juror decision-making in insanity trials. Participants (396) were presented with a case summary and psychological testimony and asked to render either a verdict of guilty or not guilty by reason of insanity in a 2 (psychosis or psychopathy) x (presence or absence of an MRI indicating a brain lesion) x (presence or absence of testimony describing a car accident that caused injury to the brain) factorial design. Defendants diagnosed with a psychotic disorder, defendants who could demonstrate the existence of a brain lesion via MRI, and defendants who had a history of brain injury were more likely to be found not guilty by reason of insanity than those defendants who did not present any neurological testimony. Participants who reported they were more influenced by the psychological and neurological testimony were almost six times more likely to render a verdict of NGRI than those participants who reported that the psychological and neurological testimony and evidence did not influence their decision regarding verdict.