There are both theoretical and neuroanatomical differences that support the distinction between the measures of impulse control. Gray (1982, 1987) and Logan (1994) have each proposed models of behavior that contrast mechanisms of behavioral activation and inhibition that may be measured with laboratory behavioral tasks. Impulsive errors made during CPT tasks are the result of failures to process stimuli completely prior to responding (Dougherty et al. 1999b; Halperin et al. 1988, 1991), which could be attributed to problems with behavioral activation. In contrast, impulsive errors made during stop tasks are failures to inhibit an already initiated response, which could be attributed to problems with behavioral inhibition (Dougherty et al. 2005a). On the other hand, an inter-temporal choice mathematical model has been proposed by neuropsychiatric and behavioral researchers (Ohmura et al. 2005; Reynolds et al. 2004; Takahashi, 2004) to explain responses on delay-discounting tasks. This model corresponds to impulsive choices made during delay-discounting tasks, defined by choosing smaller-sooner reinforcers over larger-later reinforcers. A comparative factor analysis has demonstrated that each task assesses variance unique to that particular task (Dougherty et al.
