Relatively few studies have conducted a systematic effort to examine patterns of co-variation in forms of impulsive behavior in animals or humans, and even fewer have conducted a well-designed study. In rats, two separate studies suggest that action inhibition in the 5CSRTT does not predict delay discounting ability. 255, 256 In human subjects, behavioral measures of action inhibition and delay-related decision-making did not correlate with one another or with subjective self-report measures.255 Caution should be taken with interpreting these results, however, since comparing two phenotypes to one another often magnifies the differences and minimizes the similarities. Moreover, this approach cannot separate differences in task from differences in the construct(s) intended to be measured. Instead, an ideal design for studies of this type involves multiple assessments of both related and unrelated phenotypes. Additionally, inbred rodent or human twin designs are required to separate shared genetic influences that span across tasks from other factors (see256).
