In previous work, smokers showed steeper devaluation of delayed rewards than non-smokers. While the neural correlates of this link between nicotine dependence and delay of discounting are not established, altered activity in executive networks may relate to impaired delayed gratification. The goal of this study was to examine neural correlates of discounting and their relation to nicotine dependence. Thirty-nine smokers and 33 non-smokers completed a functional magnetic resonance imaging (fMRI) intertemporal choice task in which they made individualized Hard (similarly valued), easy (dissimilarly valued), and control monetary choices. FMRI data were analyzed using a group independent component analysis and dual regression. Smokers discounted more steeply than non-smokers, although this difference was only significant among severely dependent smokers. Intertemporal choices recruited distinct left- and right-lateralized fronto-parietal networks. A group-by-difficulty interaction indicated that smokers, relative to non-smokers, exhibited less difficulty-sensitivity in the right fronto-parietal network. In contrast, smokers showed greater functional connectivity between the left fronto-parietal network and the left fronto-insular cortex. Moreover, the degree of functional connectivity between the left fronto-parietal network and left fronto-insular cortex was significantly correlated with individual differences in discounting. Thus, greater functional coupling between the anterior insula and left fronto-parietal network is a candidate neural substrate linking smoking and impulsivity. Given the anterior insula's role in interfacing cognitive and interoceptive processing, this altered functional connectivity may relate to an addiction-related bias towards immediate rewards.
Keywords: delay discounting; dual regression; fMRI; independent component analysis; nicotine dependence.
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