The relationship between reward processing and impulsivity in addiction: a functional magnetic resonance imaging study

Introduction: Evidence suggests that abnormalities in reward processing and increased impulsivity contribute to the pathophysiology of addiction. However, the relationship between the two is currently not well characterised. This study used fMRI to investigate the BOLD response during reward and inhibitory control tasks and how such responses were associated with subjective and behavioural measures of impulsivity in abstinent alcohol, cocaine and polydrug addiction. We hypothesized a negative correlation between non-drug related reward anticipation and impulsivity measures in polydrug and alcohol dependence compared with healthy controls owing to increased impulsivity and thus more inhibitory control effort needed to maintain successful abstinence. Methods: Abstinent alcohol dependent (AD, n=27), polydrug dependent (PD, n=57) and healthy control (HC, n=65) participants were recruited [1] (REC number 11/H0707/9). Participants completed a battery of impulsivity measures; the Barratt Impulsiveness Scale (BIS-11) and the Urgency, Premeditation, (lack of), Perseverance (lack of), Sensation Seeking, Positive Urgency, Impulsive Behaviour Scale (UPPS-P) to measure trait impulsivity, the Kirby Delay Discounting task to measure choice impulsivity and the Stop Signal Task (SST) to measure impulsive action. Participants also underwent fMRI scanning (3-T) using the monetary incentive delay (MID) and Go/No-go (GNG) tasks. An a-priori region of interest approach was used to image BOLD response during the following contrasts: reward anticipation>neutral anticipation and no-go/go in the rIFG, OFC and caudate. Data was analysed using ANOVA or Kruskal- Wallis tests (with Tukey or Mann-Whitney U post-hoc tests respectively) and Pearson's or Spearman's rank correlations, as appropriate. Holm-Bonferroni correction was applied. Results: There were significant group differences in the BIS-11 (pneutral anticipation and no-go>go contrasts. In the overall population, significant but weak positive correlations were observed between BOLD response for the reward anticipation>neutral anticipation and no-go>go contrast in the rIFG (r=0.208, p=0.001), OFC (r=0.219, p=0.008) and caudate (r=0.208, p=0.012). Interestingly, while these associations were observed in the HC group no such associations existed in the AD and PD groups. Finally, no significant associations were observed between subjective impulsivity measures and BOLD signal change during either task. Conclusion: The overall findings of this study suggest that there is a relationship between BOLD response during reward processing and inhibitory control. However, in contrast to our hypothesis this association was positive and was not observed in AD or PD individuals, suggesting that such an association is dysregulated in addiction. Further work is required to better understand the association between BOLD response during reward processing and impulse control. This study was funded by the MRC (G1000018) with support from GSK