Aggressive, suicidal and violent behaviour have been associated with impulsive personality and difficulty in inhibiting responses. We used functional magnetic resonance imaging (fMRI) of the whole brain to examine the neural correlates of response inhibition in 19 normal subjects as they performed a Go/NoGo task. Subjects completed Eysenck's Impulsivity Scale, Barratt's Impulsivity Scale (BIS) and behavioural impulsivity tasks. Associations between blood oxygen level dependent (BOLD) response, trait impulsivity, task performance and National Adult Reading Test (NART) IQ were investigated. Neural response during response inhibition was most prominent in the right lateral orbitofrontal cortex. Responses were also seen in superior temporal gyrus, medial orbitofrontal cortex, cingulate gyrus, and inferior parietal lobule, predominantly on the right side. Subjects with greater scores on impulsivity scales and who made more errors had greater activation of paralimbic areas during response inhibition, while less impulsive individuals and those with least errors activated higher order association areas. Exploratory factor analysis of orbital activations, personality measures and errors of commission did not reveal a unitary dimension of impulsivity. However, the strong association between posterior orbital activation and Eysenck's impulsivity score on a single factor suggests that greater engagement of right orbitofrontal cortex was needed to maintain behavioural inhibition in impulsive individuals. Lower IQ was more important than impulsivity scores in determining errors of commission during the task. Neuroimaging of brain activity during the Go/NoGo task may be useful in understanding the functional neuroanatomy and associated neurochemistry of response inhibition. It may also allow study of the effects of physical and psychological interventions on response inhibition in clinical conditions such as antisocial personality disorder.
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