The cognitive impairments described in the investigations reviewed here also make contact with what we know about the mechanisms of impulsivity as revealed by experiments with animal and human subjects (Dalley et al., 2008; Jentsch and Taylor, 1999). These include the control of prematurely activated response repertoires (as tested by continuous performance paradigms (Bjork et al., 2004; Finn et al., 2002; Robbins, 2002); choices between small immediate rewards and larger delayed reward (as tested by delay-discounting tasks) (Bjork et al., 2004; Winstanley et al., 2006a,c), as well as the gathering of adequate information before action initiation (as tested in tasks of reflection impulsivity) (Clark et al., 2006; Evenden, 1999a). Thus, findings that deficient response inhibition and risky choice in substance users are associated with altered signaling within the dorsal anterior cingulate cortex and its dorsomedial surround are consistent with observation that lesions of dorsomedial-striatal circuitry can also increase impulsive behaviors in rats (Muir et al., 1996; Rogers et al., 2001), and with evidence that the dorsal anterior cingulate cortex is involved in value-based choices in healthy adult volunteers (Rogers et al., 2004; Rushworth et al., 2004).
