Alcohol Hits You When It Is Hard: Intoxication, Task Difficulty, and Theta Brain Oscillations

BACKGROUND: Alcohol intoxication is known to impair decision making in a variety of situations. Previous neuroimaging evidence suggests that the neurofunctional system subserving controlled processing is especially vulnerable to alcohol in conflict‐evoking tasks. The present study investigated the effects of moderate alcohol intoxication on the spatiotemporal neural dynamics of event‐related total theta (4 to 7 Hz) power as a function of task difficulty. METHODS: Two variants of the Simon task manipulated incongruity via simple spatial stimulus‐response mismatch and, in a more difficult version, by combining spatial and semantic interference. Healthy social drinkers participated in both alcohol (0.6 g/kg ethanol for men, 0.55 g/kg for women) and placebo conditions in a counterbalanced design. Whole‐head magnetoencephalography (MEG) signals were acquired and event‐related total theta power was calculated on each trial with Morlet wavelets. MEG sources were estimated using anatomically constrained, noise‐normalized, spectral dynamic statistical parametric mapping. RESULTS: Longer reaction times and lower accuracy confirmed the difficulty manipulation. Response conflict (incongruity) increased and alcohol intoxication decreased event‐related theta power overall during both tasks bilaterally in the medial and ventrolateral prefrontal cortices. However, alcohol‐induced theta suppression was selective for conflict only in the more difficult task which engaged the dorsal anterior cingulate (dAC) and anterior inferolateral prefrontal cortices. Theta power correlated negatively with drinking levels and disinhibition, suggesting that cognitive control is susceptible in more impulsive individuals with higher alcohol intake. CONCLUSIONS: The spatiotemporal theta profile across the 2 tasks supports the concept of a rostrocaudal activity gradient in the medial prefrontal cortex that is modulated by task difficulty, with the dAC as the key node in the network subserving cognitive control. Conflict‐related theta power was selectively reduced by alcohol only under the more difficult task which is indicative of the alcohol‐induced impairment of conflict monitoring and top‐down regulation. Compromised executive control under alcohol may underlie a range of adverse effects including reduced competency in conflict‐inducing or complex situations.