Impulsive behaviour is a feature of a number of psychiatric disorders including attention-deficit hyperactivity disorder (ADHD), substance abuse, obsessive–compulsive disorder and borderline personality disorder (Chamberlain et al., 2005, Ersche et al., 2010 and Moeller et al., 2001). One of the most common self-report measures of impulsivity is the Barratt Impulsiveness Scale (BIS) (Patton et al., 1995), which has been implemented both in healthy and in patient groups (Koch et al., 2007, Peluso et al., 2007 and Preuss et al., 2008).
The neurochemical basis of impulsivity has been suggested to be linked to the monoaminergic system (Buckholtz et al., 2010, Cools et al., 2007, Dalley et al., 2007, Robbins and Arnsten, 2009 and Winstanley et al., 2004). Evidence from imaging studies with single-photon emission computed tomography (SPECT) has shown that serotonin transporters are associated with self-report measurements of impulsivity (Koch et al., 2007 and Lindström et al., 2004). Likewise, a role of dopamine in impulsivity is suggested in SPECT studies of ADHD. ADHD patients suffer symptoms of hyperactivity and impulsivity and have in some studies been shown to have increased availability of dopamine transporter (Dougherty et al., 1999, Dresel et al., 2000, Krause et al., 2000 and Larisch et al., 2006; however, see van Dyck et al., 2002, Volkow et al., 2007 and Volkow et al., 2009). Methylphenidate, a drug which blocks the dopamine transporter (Volkow et al., 1999), has been shown to be effective in alleviating the clinical symptoms of ADHD (Greenhill et al., 1999) whilst reducing striatal dopamine transporter availability (Krause et al., 2000). In addition, elevated dopamine transporter availability has been shown to be associated with better therapy response to methylphenidate (la Fougere et al., 2006).
However, not much is known about the dopamine system correlates of individual differences in trait impulsivity and ADHD-related traits in the non-clinical population. Studies have suggested that symptoms of ADHD and other psychiatric disorders lie on a continuum from health to illness (Markon et al., 2011 and Verdoux and van Os, 2002). A similar continuum model may be assumed in relation to impulsivity in the normal population, with clinical conditions such as ADHD, personality disorders or substance abuse at the extreme end of the spectrum (Levy et al., 1997).
Confirming such dimensional views, recent evidence revealed that trait differences in impulsivity are associated with dopamine autoreceptor availability in the midbrain in healthy subjects (Buckholtz et al., 2010), raising the question whether trait differences in impulsivity might also be associated with other mechanisms involved in dopamine signalling in the brain, such as the dopamine transporter. Thus based on the continuum hypotheses of psychiatric disorders, it might be expected that an association may be present between trait impulsivity and dopamine transporter availability in healthy subjects that reflects changes seen in clinical conditions such as ADHD, substance abuse and obsessive–compulsive disorder (Amsterdam and Newberg, 2007, Kim et al., 2003 and Malison et al., 1998).
However, only two studies to date have investigated the association between impulsivity or related traits and dopamine transporter availability in the non-clinical population and no prior association has been found (Burke et al., 2011 and Lindström et al., 2004) despite suggestive evidence of such a relationship from clinical studies (Dougherty et al., 1999, Krause, 2008 and Krause et al., 2000). Therefore, the present study aimed to further add to this literature by examining the association between dopamine transporter availability and impulsivity-related traits. We used [123I] FP-CIT SPECT and measured impulsivity (Patton et al., 1995) and ADHD-related traits (Kessler et al., 2005) using self-report questionnaires in a carefully screened, non-clinical sample. Additionally, in order to confirm the specificity of any such findings with regards to general psychopathology (Claridge and Davis, 2001), we also controlled for negative trait emotionality, or neuroticism, in the association between impulsivity and striatal dopamine transporters.
