Effects of Alcohol Intoxication on Response Conflict in a Flanker Task

Events evoke seamlessly integrated stimulus evaluation and response preparation processing streams, guided by regulative functions that change behavior flexibly in accord with the internal goals and contextual demands. The neural basis of the effects of alcohol intoxication on these processing streams is poorly understood, despite the evidence of alcohol's deleterious effects on both attention and motor control. In an attempt to separate and examine relative susceptibility of these two dimensions, we employed a color version of the Eriksen flanker task that manipulated compatibility at the stimulus- and response-processing levels. Functional magnetic resonance imaging (fMRI) was performed in healthy social drinkers as they participated in both alcohol (0.6 g/kg ethanol for men, 0.55 g/kg for women) and placebo conditions in a counterbalanced design. Alcohol increased reaction times to response-level incongruity and decreased accuracy overall. Relative to the no-conflict condition, the observed brain activity was predominantly evoked by response-related conflict in medial prefrontal and lateral prefrontal cortices under placebo, in agreement with extensive evidence of their role in conflict processing. Activity evoked by response incongruity in the medial frontal cortex and insula was insignificant under alcohol, indicating its interference with response inhibition and preparation. Conversely, activity in ventrolateral prefrontal and premotor areas was relatively greater under alcohol than placebo, suggesting their compensatory engagement. This finding is consistent with the compensatory prefrontal activity increase found in studies with chronic alcoholic individuals, indicating functional reorganization with a goal of optimizing response strategy. These results delineate functional differences and selective susceptibility of a prefrontal network subserving response-level conflict processing. Our findings are incompatible with notions that moderate alcohol primarily affects attentional or stimulus-related processing and argue instead that its primary influence is on response inhibition, selection, and execution, with ramifications for the models of behavioral self-control and the inability to refrain from drinking.