At the current time, it is unclear whether these different forms of impulsivity constitute a set of predisposing traits that increase the probability of developing clinically significant illness, or instead represent the cumulative effects of previous illness episodes; in the case of substance use, it may be that the cumulative effects of alcohol and drug use promote the expression impulsive behavior. Experiments with animal models are needed to test between these possibilities. However, at least in the case of stimulants, reduced D2 receptor expression promotes impulsive behavior and drug self-administration (Dalley et al., 2007a) while drug administration seems to have both short and long-term effects on subsequent cognitive (attentional) function (Dalley et al., 2007b). Consistent with the possibility that heightened impulsiveness might be a predisposing trait (or set of traits), Saunders and colleagues (2008) report that first-degree relatives of individuals with alcoholism showed lower socialization scores than individuals with no such familial risk, alongside an increased number of commission errors during performance of a go/no-go reaction time task (Saunders et al., 2008). Other data suggest that such impairments might also
