Medial Orbitofrontal Cortex Gray Matter Is Reduced in Abstinent Substance-Dependent Individuals

Background: Chronic exposure to drugs of addiction induces cellular adaptations in orbitofrontal cortex (OFC) and associated limbic-prefrontal pathways that might underlie abuse-related behavior. A propensity to make risky decisions in spite of substantial negative consequences might be mediated by medial OFC dysfunction in substance-dependent individuals (SDI). We tested the hypothesis that medial OFC gray matter (GM) volume would be lower in SDI compared with control subjects. Methods: Nineteen SDI and 20 control subjects participated. The SDI were dependent on two or more substances, most often cocaine, amphetamine, and alcohol, with mean duration of abstinence 4.7,2.4, and 3.2 years, respectively. High-resolution T1-weighted images were acquired on a 3-T magnetic resonance system. Image processing and analyses were conducted with voxel-based morphometry (VBM) implemented in Statistical Parametric Mapping (SPM) 5. Differences in regional GM volume were tested with an analysis of covariance model, co-varying for global GM and age. Statistical maps were set at p < .05, corrected for multiple comparisons. Medial OFC GM volume was correlated with behavioral performance on a modified gambling task. Results: There was lower GM volume specifically in bilateral medial OFC in SDI compared with control subjects. There was a small but significant correlation between medial OFC GM and persistence of playing high-risk decks on a modified gambling task. Conclusions: This is the first study to use VBM with whole brain correction for multiple comparisons in SDI after prolonged abstinence. Reduced medial OFC GM might reflect long-term adaptations within the reward-learning circuit underlying pathological decision-making in substance dependence.