Neuropsychologia 41 (2003) 1959–1966 Response inhibition and impulsivity: an fMRI study N.R. Horn a,∗ , M. Dolan a , R. Elliott a , J.F.W. Deakin a , P.W.R. Woodruff a,b a Neuroscience and Psychiatry Unit, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK b SCANlab, Academic Department of Psychiatry, The Longley Centre, University of Sheffield, Norwood Grange Road, Sheffield S5 7JT, UK Received 14 August 2001; received in revised form 6 March 2003; accepted 11 March 2003 Abstract 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. © 2003 Elsevier Ltd. All rights reserved. Keywords: Go/NoGo; Impulsivity; Functional magnetic resonance imaging; Orbitofrontal cortex; Frontal lobe; Antisocial personality disorder 1. Introduction Impulsivity is a multidimensional concept that incor- porates failure of response inhibition, rapid processing of information, novelty seeking, and inability to delay gratifi- cation (Barratt, 1985, 1994). Impulsivity is one of the defin- ing characteristics of a number of psychiatric diagnoses, particularly borderline and antisocial personality disorders (Stein, Hollander, & Liebowit 1995; Stein, Towney, & Hollander, 1995). Poor impulse control correlates signif- icantly with suicidal, violent and aggressive behaviour (Plutchik & Van Praag, 1989, 1995) and is an increas- ingly important aspect of risk assessment in a variety of clinical situations, including assessment of dangerousness (Monahan et al., 2000). Most attempts to measure impul- sivity rely on psychometric self-report trait measures. Some ∗ Corresponding author. Department of Psychiatry, Royal Liverpool Uni- versity Hospital, Liverpool L69 3GA, UK. Tel.: +44-151-7065151; fax: +44-151-7093765. E-mail address: neilhorn@liverpool.ac.uk (N.R. Horn). behavioural impulsivity tasks have been developed, measur- ing preference for a smaller more immediate reward over a delayed larger reward, and impaired motor inhibition, how- ever, psychometric and behavioural impulsivity measures do not correlate well with each other (Barratt & Patton, 1983; Barratt, Stanford, Kent, & Felthous, 1997). Behavioural im- pulsivity tasks tend to have low test–retest reliability, apart from the Go/NoGo task, which has reasonable temporal stability (Kindlon, Mezzacappa, & Earls, 1995). Impulsivity is a feature of damage to the frontal lobe and an “acquired sociopathic” syndrome has been described following ventromedial frontal lobe lesions (Damasio, Tranel, & Damasio, 1990; Grafman et al., 1996; Paradiso, Chemerinski, Yazici, Tartaro, & Robinson, 1999). This has lead to suggestions that impaired ventromedial frontal lobe function may contribute to poor impulse control in antiso- cial personality disorders (Damasio, 2000). In support of this notion a variety of neuropsychological deficits have been reported in antisocial populations (Morgan & Lilien- feld, 2000). Neuroimaging studies in this population report a reduction in prefrontal metabolism (Raine, Buchsbaum, 0028-3932/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0028-3932(03)00077-0