Background. Reduced serotonin (5-HT) function and deficits on neuropsychological tasks have been separately reported in antisocial populations. We investigated whether these impairments are independent or associated factors underlying impulsivity in aggressive personality disordered (PD) offenders and healthy controls and whether there are associated changes in quantitative brain measures.

Methods. This study reports on the findings from a sample of 51 PD offenders and 24 controls, recruited from maximum security psychiatric hospitals, who were characterized using the Special Hospital Assessment of Personality and Socialisation (SHAPS). Subjects underwent assessment of 5-HT function (prolactin response to D-fenfluramine challenge), neuropsychological testing and had a diagnostic MRI scan. Of this sample 19 controls and 24 patients also had quantitative measurement of frontal and temporal lobe volumes on magnetic resonance imaging (MRI).

Results. Non-psychopathic (low-impulsive) aggressive PDs had enhanced 5-HT function compared with controls and highly impulsive aggressive psychopaths. Primary and secondary psychopaths had poorer executive/frontal, but not memory/temporal neuropsychological function than controls and non-psychopaths. There were no significant group differences in frontal or temporal lobe brain volumes. Although impulsivity and aggression are correlated constructs impulsivity appeared to be related to both executive function and 5-HT function, while aggression only correlated inversely with executive/frontal and memory/temporal function. 5-HT did not directly correlate with frontal or temporal volume or function.

Conclusion. Impulsivity appears to be contributed to by both impaired neuropsychological function and 5-HT function. Impaired neuropsychological function alone makes a contribution to aggression. Treatment needs to take account of the neuropsychological and biochemical deficits in this challenging population.