Imaging temporal discounting in smokers and nonsmokers

DESCRIPTION (provided by applicant): The overall aim of the proposed research is to identify the neural substrates of impulsive decision making associated with chronic exposure to drugs of abuse. Such information is potentially important for understanding the development and cessation of habitual drug use. Furthermore, it may provide important insights into the interaction of motivational systems and neurocognitive mechanisms of executive control, which are central to a number of disorders such as drug abuse, ADHD and pathological gambling. In this application, impulsive decision making will be assessed using a temporal discounting paradigm in which we measure preference for small rewards available either immediately or soon versus larger rewards available much later. Accordingly, the specific aim of the research proposed here is to identify differences in brain activation patterns in smokers and nonsmokers corresponding to the behavioral differences on a temporal discounting task using functional magnetic resonance imaging (fMRI) techniques. The study will use an event-related design to compare activation patterns during choice tasks designed to separate processing associate with temporal discounting from processing of reward dimensions like size and relative reward immediacy. We hypothesize that, during temporal discounting, when one reward alternative is available immediately and the other delayed, smokers will exhibit higher levels of activation in ventral striatum (esp. nucleus accumbens), medial OFC, medial prefrontal cortex, posterior cingulate cortex than nonsmokers making these choices (" areas": McClure et al., 2004;2007). In contrast, nonsmokers will exhibit higher levels of activation in ventrolateral and dorsolateral prefrontal cortex, right lateral OFC and posterior parietal cortex (" areas") than smokers. During temporal discounting when both reward alternatives are delayed, we predict that nonsmokers will also exhibit higher levels of activation in the areas compared to smokers. The PI is already engaged in funded research examining the behavioral mechanisms linking temporal discounting and cigarette smoking. The proposed research would permit her to take the first step towards exploring the neural regions and inter-relationships between these regions using fMRI techniques. Potential health impact: This research will identify areas of the brain that are involved when individuals evaluate the subjective value of alternatives differing in their reward size and the delay until their availability. It will also identify areas that are involved when individuals express a preference between the alternatives, and any differences between smokers and nonsmokers in activation patterns underlying these preferences. Understanding which structures are involved in such decision making and their connectivity, may suggest individualized treatment targets for people exhibiting impulsive decision-making due to chronic drug use, accident or stroke.