Investigating the organization of trait aggression and impulsivity in the prefrontal cortex (PFC) advances our understanding of the neuropsychobiology of self-control. While the orbital aspect of the PFC (OFC) has received attention, there is reason to believe the lateral aspect is also relevant. In the current study using magnetic resonance imaging, gray matter volumes in lateral PFC (LPFC) were derived in a heterogeneous male psychiatric sample (N=36) in which OFC volumes had previously been reported. In an analysis using self-report measures of trait impulsivity and aggression, the left LPFC accounted for significant variance in attentional aspects of impulsivity (13%) and aggression (10%) but not motor aspects of impulsivity, as hypothesized. The OFC was associated with motor impulsivity (left-20%; right-14%) and was also more robustly associated with aggression (left-36%; right-16%). A social/emotional information processing model was explored, based upon whether the LPFC or the OFC depended upon one another for their association to trait aggression and impulsivity. It was demonstrated that association of the LPFC to both aggression and attentional impulsivity depended upon the OFC, while the converse was not supported. The LPFC appears relevant to the higher-order aspects of a cortical self-control network, and that relevance is dependent upon the robust contribution of the OFC.

BACKGROUND/HYPOTHESIS: Divergent thinking is an important measurable component of creativity. This study tested the postulate that divergent thinking depends on large distributed inter- and intra-hemispheric networks. Although preliminary evidence supports increased brain connectivity during divergent thinking, the neural correlates of this characteristic have not been entirely specified. It was predicted that visuospatial divergent thinking would correlate with right hemisphere white matter volume (WMV) and with the size of the corpus callosum (CC). METHODS: Volumetric magnetic resonance imaging (MRI) analyses and the Torrance Tests of Creative Thinking (TTCT) were completed among 21 normal right-handed adult males. RESULTS: TTCT scores correlated negatively with the size of the CC and were not correlated with right or, incidentally, left WMV. CONCLUSIONS: Although these results were not predicted, perhaps, as suggested by Bogen and Bogen (1988), decreased callosal connectivity enhances hemispheric specialization, which benefits the incubation of ideas that are critical for the divergent-thinking component of creativity, and it is the momentary inhibition of this hemispheric independence that accounts for the illumination that is part of the innovative stage of creativity. Alternatively, decreased CC size may reflect more selective developmental pruning, thereby facilitating efficient functional connectivity.

The prefrontal cortex (PFC) is the seat of higher level control operations, with recognition and working memory processes critical to those operations. While not strictly organized by the principle of localization, certain functions are clearly more associated with one region than another within PFC dynamic systems. We set out to test the hypothesis that active visual memory comparison (making judgments of novelty) was most associated with the ventrolateral prefrontal cortex (VLPFC), while the monitoring and manipulation of visual information was most associated with the mid-dorsolateral prefrontal cortex (mid-DLPFC). The current study used magnetic resonance volumetry to define the VLPFC and mid-DLPFC as regions of interest (ROIs), and analyzed those in relation to types of visual memory processes. We observed a functional dissociation of working memory within the PFC corresponding to comparison versus monitoring processes. One of the blocks of the monitoring and manipulation task showed a significant positive relationship with left, right, and total mid-DLPFC volume, with no significant relationship to the VLPFC. Performance on a memory comparison task bore a significant positive relationship with right and total VLPFC volume, and no relationship with the mid-DLPFC.

The association between orbital frontal cortex (OFC) volume and aggression was investigated in an at-risk psychiatric population. Forty-one psychiatric patients were referred for magnetic resonance imaging and a standardized psychometric assessment of aggression (Lifetime History of Aggression-Revised). Nineteen matched controls had lower levels of aggression and greater OFC volume, establishing the appropriateness of the psychiatric group for studying aggression pathophysiology. Consistent with study hypotheses, left OFC gray matter volume predicted 34% of the variance in self-reported aggression ratings. When impulsivity was not controlled for, left OFC gray matter only accounted for 26% of aggression variance, suggesting a complex relationship between impulsivity and OFC-aggression pathophysiology. Contrary to study hypotheses, right OFC gray matter volume did not predict degree of aggressive behavior. Current models do not account for lateralization, yet this may be quite important. Greater consideration should be given to laterality in OFC regulation of social/emotional behavior. Regulatory focus theory, positing two motivational systems, promotion and prevention, lateralized to the left and right hemispheres, respectively, may provide an explanatory framework for these results. Dysregulation of the left hemisphere 'promotion' motivational system may help to explain the aggressive behavior present in psychiatric populations.

The association between orbital frontal cortex (OFC) volume and aggression and impulsivity was investigated among a heterogeneous group of non-psychotic psychiatric clients. Fifteen non-psychotic subjects from two different psychiatric clinics (New England Medical Center and Lemuel Shattuck Hospital) with a variety of diagnoses were sequentially referred for magnetic resonance imaging (MRI) for clinical purposes. This convenience sample, clinically stable at the time of evaluation, received a standardized psychiatric diagnostic interview, aggression and impulsivity psychometrics (Barratt Impulsivity, Lifetime History of Aggression, and Buss-Perry Aggression scales), and an MRI protocol with image analysis. OFC gray matter volume, total as well as left and right, was significantly and positively associated with motor impulsivity. OFC asymmetry was associated with aggression, though total, left, and right OFC volume measurements were not. For subjects without affective disorder, there was a strong and positive association of the OFC to motor and no-planning subscales of the Barratt Impulsivity Scale. For subjects with affective disorder, there was a strong association of OFC asymmetry to both of the aggression psychometrics. Consistent with expectation, results are suggestive of OFC involvement in the neural circuitry of impulsivity and aggression. The findings suggest a dissociation of the role of the OFC in relation to aggression and impulsivity, such that the OFC may play a part in the regulation of aggressive behavior and a generative role in impulsive behavior.