Neural correlates of reward magnitude and delay during a probabilistic delay discounting task in alcohol use disorder

Abstract

Rationale: Alcohol-use disorder (AUD) is associated with the propensity to choose smaller sooner options on the delay discounting task. It is unclear, however, how inherent risk underlies delay discounting behavior. As impulsive choice is a hallmark feature in AUD, it is important to understand the neural response to reward and delay while accounting for risk in impulsive decision-making.

Objective: This study examined activation associated with delay and reward magnitude, while controlling for risk in a probabilistic delay discounting task in AUD and examined if differences in activation were associated with treatment outcomes.

Methods: Thirty-nine recently abstinent alcohol-dependent volunteers and 46 controls completed a probabilistic delay discounting task paired with functional magnetic resonance imaging. Alcohol use was collected using a self-report journal for 3 months following baseline scan.

Results: During delay stimulus presentations, Controls exhibited greater activation compared to the Alcohol group notably in the anterior insula, middle/dorsal anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (PFC), and inferior parietal lobule. For magnitude, the Alcohol group exhibited greater activation than Controls primarily in medial PFC, rostral ACC, left posterior parietal cortex, and right precuneus. Within the Alcohol group, alcohol craving severity negatively correlated with right lateral PFC activation during reward magnitude in individuals who completed the 3-month study without relapse, while non-completers showed the opposite relationship.

Conclusions: The results of this study extend previous findings that alcohol use disorder is associated with differences in activation during an immediate or delayed choice by delineating activation associated with the parameters of impulsive choice.

Keywords: Alcohol; Craving; Delay discounting; Impulsivity; Probability discounting; Relapse.

Fig. 1. Probabilistic Delay Discounting task (PDD) with flow for fMRI presentation

The surface that best separates the choices of the immediate, certain reward (green) from choices of the alternate reward (red) was determined

Fig. 2. Group differences in activation elicited by Magnitude and Delay during the PDD

a. Magnitude-elicited activation was similar across Control and Alcohol groups; however, the Control group showed additional and more prominent regions of activation. Group comparisons showed the Alcohol group exhibited greater activation than Controls in the calcarine, lingual, fusiform, and occipital gyri, cuneus, precuneus, superior medial gyrus, rostral ACC (rACC), right superior temporal, angular, and supramarginal gyri, and right pre and postcentral gyrus, while the Control Group showed no significant regions of greater activation b. Delay-elicited activation was significant in multiple regions in the Control group, while the Alcohol group showed no regions of significant activation. Group comparisons showed the Control group exhibited greater activation than the Alcohol group in the occipital lobe, insula, putamen, left thalamus, inferior frontal gyrus, superior medial gyrus, supplementary motor area, right middle frontal gyrus, anterior and middle cingulate cortices, right superior and inferior parietal lobule, right supramarginal gyrus and pre- and postcentral gyri, while the Alcohol group showed no significant regions of greater activation.

Fig. 3. Group differences in anterior cingulate cortex activation

a. Controls showed greater activation than the Alcohol group in the dorsal anterior cingulate/middle cingulate cortices during delay b. Alcohol group showed greater activation than controls in the rostral anterior cingulate cortex during magnitude

Fig. 4. Group differences in the relationship between activation and craving

Alcohol craving was assessed using a Visual Analog Scale (VAS) ranging from 0 (no craving) to 100 (most intense craving imaginable). Scatterplot illustrates the group interaction and shows differences between study Completers and Non-Completers on the relationship between craving and beta values for right lateral prefrontal cortex (LPFC) from the whole-brain regression during magnitude (group × activation interaction)