Abstract
BackgroundDelayed reward discounting (DRD), the degree to which future rewards are discounted relative to immediate rewards, is used as an index of impulsive decision-making and has been associated with a number of problematic health behaviors. Given the robust behavioral association between DRD and addictive behavior, there is an expanding literature investigating the differences in the functional and structural correlates of DRD in the brain between addicted and healthy individuals. However, there has yet to be a systematic review which characterizes differences in regional brain activation, functional connectivity, and structure and places them in the larger context of the DRD literature. The objective of this systematic review is to summarize and critically appraise the existing literature examining differences between addicted and healthy individuals in the neural correlates of DRD using magnetic resonance imaging (MRI) or functional magnetic resonance imaging (fMRI).MethodsA systematic search strategy will be implemented that uses Boolean search terms in PubMed/MEDLINE and PsycINFO, as well as manual search methods, to identify the studies comprehensively. This review will include studies using MRI or fMRI in humans to directly compare brain activation, functional connectivity, or structure in relation to DRD between addicted and healthy individuals or continuously assess addiction severity in the context of DRD. Two independent reviewers will determine studies that meet the inclusion criteria for this review, extract data from included studies, and assess the quality of included studies using the Grading of Recommendations Assessment, Development and Evaluation framework. Then, narrative review will be used to explicate the differences in structural and functional correlates of DRD implicated by the literature and assess the strength of evidence for this conclusion.DiscussionThis review will provide a needed critical exegesis of the MRI studies that have been conducted investigating brain differences in addictive behavior in relation to healthy samples in the context of DRD. This will provide clarity on the elements of neural activation, connectivity, and structure that are most implicated in the differences in DRD seen in addicted individuals.Systematic review registrationPROSPERO CRD42017056857
Highlights
Delayed reward discounting (DRD), the degree to which future rewards are discounted relative to immediate rewards, is used as an index of impulsive decision-making and has been associated with a number of problematic health behaviors
Delayed reward discounting (DRD), the degree to which a future reward is discounted relative to an immediate reward, is often measured by a series of choices between smaller rewards that are immediately available and delayed rewards available at some time in the future, with money being the most commonly used reward [4]
A recent model integrating these findings describes the neural process of DRD decision-making as being an emergent property of these neural networks interacting with each other, as well as sensory and motor systems, in recursive loops to use past experiences to assess the subjective value of the two options, compare them, and respond appropriately based on that comparison [21]
Summary
Delayed reward discounting (DRD), the degree to which future rewards are discounted relative to immediate rewards, is used as an index of impulsive decision-making and has been associated with a number of problematic health behaviors. Delayed reward discounting (DRD), the degree to which a future reward is discounted relative to an immediate reward, is often measured by a series of choices between smaller rewards that are immediately available and delayed rewards available at some time in the future, with money being the most commonly used reward [4] In such a paradigm, greater devaluation of the delayed reward are conceptualized as indicating greater impulsivity of decision-making and a preference for immediate gratification [5] and as a form of impatience [6]. DRD has been suggested as a trans-disease process that links addiction with other disorders and problematic outcomes that include maladaptive decision-making [14]. This makes understanding the biological processes underlying DRD in clinical populations a vital goal in order to understand the nature of this dysregulated decision-making preference and to developing treatments that can reduce morbidity associated with addiction and other disorders
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