Dopamine facilitation of incentive motivation lays the very foundation of normal goal-oriented behavior, and is suspected of being involved directly or indirectly in an array of abnormal behavioral conditions. Incentive-motivated behavior is facilitated by corticolimbic glutamatergic afferents that carry the salient context predictive of reward to DA neurons in the ventral tegmental area (VTA) and to spiny neurons in the nucleus accumbens (NAS). Much animal work demonstrates that individual differences in VTA DA and NAS DA functioning modulate the extent to which salient incentive contexts a) are bound to VTA and NAS neurons, and hence b) facilitate the behavioral expression of incentive motivational processes in the NAS. We demonstrated (Depue & Collins, 1999) that the foundation of the major personality trait of extraversion is positive incentive motivation, and that variation in both of these is associated with individual differences in DA functioning. Therefore, it can be hypothesized that variation in extraverted affect and behavior is associated with variation in the strength to which salient context comes to facilitate incentive motivational processes. The proposed studies specifically test this hypothesis through four experimental studies that assess a) the extent to which context is paired with a methylphenidate-facilitated incentive motivational state, b) dose dependence of these effects, and the extent to which the effects are modified by c) latent inhibition and d) extinction processes. Significance of the work derives from its development of new methodology, performance measures, and pharmacological designs to study context-motivational associations in humans. Also, these studies are designed to provide information that may enlighten several psychiatric problems that may involve a contribution of DA to, and contextual facilitation of, disordered behavior. Recent research raises the possibility that determination of DA-behavior relations could have benefit in understanding, and perhaps in treating, pathological forms of personality disorders, some forms of affective disorders, and schizophrenic positive symptoms. Furthermore, the proposed studies may have direct implications for understanding and modeling the genetic-experiential interactive liabilities to alcohol and psychostimulant substance abuse that may depend on the sensitivity of DA receptor systems in interaction with environmental context.
