Impulsive aggression is characterized by an inability to regulate affect as well as aggressive impulses, and is highly comorbid with other mental disorders including depression, suicidal behavior, and substance abuse. In an effort to elucidate the neurobiological underpinnings of impulsive aggression and to help account for its connections with these other disorders, this paper reviews relevant biochemical, brain imaging, and genetic studies. The review suggests that dysfunctional interactions between serotonin and dopamine systems in the prefrontal cortex may be an important mechanism underlying the link between impulsive aggression and its comorbid disorders. Specifically, serotonin hypofunction may represent a biochemical trait that predisposes individuals to impulsive aggression, with dopamine hyperfunction contributing in an additive fashion to the serotonergic deficit. The current paper proposes a modified diathesis-stress model of impulsive aggression in which the underlying biological diathesis may be deficient serotonergic function in the ventral prefrontal cortex. This underlying disposition can be manifested behaviorally as impulsive aggression towards oneself and others, and as depression under precipitating life stressors. Substance abuse associated with impulsive aggression is understood in the context of dopamine dysregulation resulting from serotonergic deficiency. Also discussed are future research directions in the neurobiology of impulsive aggression and its comorbid disorders.

The utility of psychopathy measures in predicting violence is largely explained by their assessment of social deviance (e.g., antisocial behavior; disinhibition). A key question is whether social deviance interacts with the core interpersonal-affective traits of psychopathy to predict violence. Do core psychopathic traits multiply the (already high) risk of violence among disinhibited individuals with a dense history of misbehavior? This meta-analysis of 32 effect sizes (N = 10,555) tested whether an interaction between the Psychopathy Checklist-Revised (PCL-R; R. D. Hare, 2003) Interpersonal-Affective and Social Deviance scales predicted violence beyond the simple additive effects of each scale. Results indicate that Social Deviance is more uniquely predictive of violence (d = .40) than Interpersonal-Affective traits (d = .11), and these two scales do not interact (d = .00) to increase power in predicting violence. In fact, Social Deviance alone would predict better than the Interpersonal-Affective scale and any interaction in 81% and 96% of studies, respectively. These findings have fundamental practical implications for risk assessment and theoretical implications for some conceptualizations of psychopathy.

Many programs for offenders with mental illness (OMIs) seem to assume that serious mental illness directly causes criminal justice involvement. To help evaluate this assumption, we assessed a matched sample of 221 parolees with and without mental illness and then followed them for over 1 year to track recidivism. First, compared with their relatively healthy counterparts, OMIs were equally likely to be rearrested, but were more likely to return to prison custody. Second, beyond risk factors unique to mental illness (e.g., acute symptoms; operationalized with part of the Historical-Clinical-Risk Management-20; Webster, Douglas, Eaves, & Hart, 1997), OMIs also had significantly more general risk factors for recidivism (e.g., antisocial pattern; operationalized with the Level of Service/Case Management Inventory; Andrews, Bonta, & Wormith, 2004) than offenders without mental illness. Third, these general risk factors significantly predicted recidivism, with no incremental utility added by risk factors unique to mental illness. Implications for broadening the policy model to explicitly target general risk factors for recidivism such as antisocial traits are discussed.

A growing body of research suggests that high quality dual role relationships between community corrections officers and offenders reduce risk of recidivism. This study assesses whether this finding generalizes from offenders with mental illness to their relatively healthy counterparts. More importantly, this study tests the possibility that this finding is spurious, reflecting the influence of pre-existing offender characteristics more than a promising principle of practice. In this study of 109 parolees without mental illness, the authors found that (a) firm, fair, and caring relationships protect against rearrest, and (b) do so even after accounting for offenders' pre-existing personality traits and risk for recidivism. These findings are consistent with the theoretical notion that good dual role relationships are an essential element of core correctional practice, even (or particularly) for difficult or high risk offenders.

Although offenders with mental illness are overrepresented in the criminal justice system, psychiatric symptoms relate weakly to criminal behavior at the group level. In this study of 143 offenders with mental illness, we use data from intensive interviews and record reviews to examine how often and how consistently symptoms lead directly to criminal behavior. First, crimes rarely were directly motivated by symptoms, particularly when the definition of symptoms excluded externalizing features that are not unique to Axis I illness. Specifically, of the 429 crimes coded, 4% related directly to psychosis, 3% related directly to depression, and 10% related directly to bipolar disorder (including impulsivity). Second, within offenders, crimes varied in the degree to which they were directly motivated by symptoms. These findings suggest that programs will be most effective in reducing recidivism if they expand beyond psychiatric symptoms to address strong variable risk factors for crime like antisocial traits.