Outcomes that are delayed tend to be less valuable than more immediate outcomes because waiting is associated with risk;this phenomenon is known as temporal discounting. However, there are occasions where waiting can be worthwhile, especially when the delayed outcome is much more valuable than the immediate outcome. People and animals are frequently confronted with choices between outcomes that may differ in delay and amount. There are a number of individual difference variables that are associated with differences in discounting rates including Attention Deficit/Hyperactivity Disorder (AHDH), drug addiction, and gambling. Impulsive individuals are less able to wait for outcomes and thus show a bias to choose shorter-delayed options even when those outcomes are much less profitable. As a result, impulsivity increases the risk of poor lifestyle choices (e.g., poor diet, gambling, drug taking) and inept money management. The present proposal seeks to advance the understanding of temporal discounting and impulsive choice by implementing screening methods to identify the source of impulsive choice. This research is driven by the observation that there are two distinct pathways to impulsivity, one through deficits in reward processing and one through deficits in temporal processing. Initial studies will develop methods for screening individuals for impulsive tendencies and identifying the key deficits associated with impulsivity in the timing and/or reward processing systems. An additional set of studies will develop targeted therapeutic interventions to redress deficits in timing and/or reward processing. Such treatments could be applied to individuals exhibiting disorders such as ADHD, and with normal individuals with a tendency towards impulsive choice to reduce the risk of the pursuit of poor lifestyle choices such as drug use/abuse, gambling, etc. A final set of studies will examine the mechanisms that underlie the effect of reward processing on choice by pinpointing the nature of the deficits in reward processing associated with neurotoxic lesions of the nucleus accumbens core, which has been identified as the primary candidate structure for the computation of reward value in temporal discounting. Determining the exact nature of the reward processing deficits associated with nucleus accumbens lesions will promote the further development of targeted therapeutic techniques for use with ADHD and other disorders that undermine self-control. The combined set of studies will significantly advance our understanding of factors that promote self- control vs. impulsive choice in temporal discounting tasks and provide a significant foundation for the development of specific therapeutic techniques designed to target the key systems involved in the computation of reward value in impulsive choice situations.
This project aims to implement screening methods for identifying the underlying source of individual differences in impulsive choice behavior, to develop targeted therapeutic techniques for improving deficits in reward processing and temporal processing, and to further understand the role of the nucleus accumbens core in the computation of reward value in impulsive choice situations. The results are potentially significant for understanding and treating disorders which result in increased impulsivity such as ADHD and impulsive personality disorder as well as pinpointing factors that affect choice in normal individuals. In addition, differences in temporal discounting have been clearly linked to drug addiction and gambling and unravelling the underlying source of these links has the potential to better understand and rectify those factors that lead to the formation and persistence of addictive tendencies.
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