One of the most promising areas of work described above is the research that identifies aspects of impulsive behavior as a quantitative indicator of liability for the initiation of substance use, of its transition to a more compulsive form of substance abuse and of successful treatment of substance dependence. Because impulsivity predates substance use in many circumstances and because impulsivity is itself a heritable trait,272 the discovery of genetic influences on impulsive behavior is crucial. Using human subjects, studies of related individuals (particularly monozygotic and dizygotic twins) can be used to model the genetic relationships between putatively distinct forms of impulsive behaviors and substance use, abuse and dependence. In the pre-clinical laboratory, isogenic rodent strains (inbred rats and mice)256, 273 or pedigreed non-human primates274, 275 can also be used to separate genetic from shared environmental factors. Moreover, advanced lines of mice – including recombinant inbred mice,276, 277 the hybrid mouse diversity panel278 and the diversity outcross279 – are now available for identifying the genetic and genomic factors that may be unique to, or shared between, measures of impulsivity that each
