Shining the spotlight on the dark side of impulsivity

Rapid decisions and actions are often necessary to ensure time-limited opportunities are not squandered. However, when behaviour is persistently rash, risky and invariant of its consequences (i.e. impulsive), negative impacts can arise and indeed underlie such disorders as pathological gambling, drug addiction, attention-deficit/hyperactivity disorder (ADHD), and bipolar disorder. But how do we define impulsivity? Since the resurgence of impulsivity research in the late nineteen nineties (Evenden, 1999), the field has struggled to reach a consensus on the classification and assessment of impulsivity traits beyond subjective self-report (e.g. the Barrett Impulsiveness Scale or BIS). While multiple forms of impulsivity, each engaging distinct brain circuities, are broadly acknowledged (Dalley and Robbins, 2017), there is still much that we do not understand about the brain mechanisms of different impulsivity subtypes. In this special issue on Addiction two papers deal with specific facets of impulsivity and their relations with drug addiction, including alcoholism and the perennial chicken-and-egg problem of causality (Herman and Duka, 2018; Paasche et al., 2018). Thus while impulsivity may be a consequence of drug use, it may also predispose individuals to compulsive drug use or the ‘dark side’ of addiction (Koob and Le Moal, 2005).JWD acknowledges funding from the UK Medical Research Council (MRC grants G0701500, G0802729, G1002231), Boehringer Ingelheim Pharma GmbH, and a joint award from the MRC (G1000183) and Wellcome Trust (093875/Z/10/Z) to the Behavioural and Clinical Neuroscience Institute at Cambridge University