Neuropsychological and Intellectual Differences Between Types of Murderers: Affective/Impulsive Versus Predatory/ Instrumental (Premeditated) Homicide

The notion that affective/impulsive violence and predatory/instrumental violence constitute distinct behavioral phenotypes has been supported in the forensic literature. Prior research suggests that offenders committing affective/impulsive homicide exhibit differing patterns of anomalous regional brain activation and decreased executive functions relative to predatory/instrumental homicide offenders. However, no prior research has examined the extent to which murderers who kill impulsively versus those who kill as the result of the execution of a premeditated strategic plan differ with regard to other neuropsychological functions and intelligence. Based on established criteria, we classified 77 murderers into affective/impulsive and predatory/instrumental groups, and compared their performance on standardized measures of intelligence and neuropsychological functioning. Results revealed significant differences between the affective/impulsive group (mean Full Scale IQ = 79) and the predatory/instrumental group (mean Full Scale IQ = 93) on indices of intelligence, memory, attention, and executive functioning. Most differences remained significant after controlling for relevant background factors.