Upon consideration of the unconditioned and particularly the conditioned stimuli that have been proposed to participate in the generation of incentive motivational states and, by extension, of extraversion, the nature of the contribution of NAS DA becomes less clear. Different kinds of conditioned stimuli can also exert strong control over the expression of behavioral sensitization. How might such stimuli affect the ability of experience-dependent processes to introduce stable individual differences in the development and expression of extraversion trait levels?