Cathodal Transcranial Direct Current Stimulation Does Not Change Implicit Associations Against Alcohol in Alcohol Use Disorder: A Preregistered Clinical Trial

Addictive behaviour is shaped by the dynamic interaction of implicit, bottom-up and explicit, top-down cognitive processes. In alcohol use disorder (AUD), implicit alcohol-related associations have been shown to predict increased subsequent alcohol consumption and are linked to the risk of relapse. Explicit cognitive processes, exerting prefrontal top-down control, are particularly significant during the critical period following the decision to abstain. This study aims to map implicit and explicit cognitive processes in recently abstinent individuals with AUD and to explore the effect of cathodal transcranial direct current stimulation (tDCS) on implicit associations by modulating top-down control. In this preregistered, double-blind, sham-controlled clinical trial, 30 abstinent individuals with AUD participated in two experimental sessions. They received either 2 mA cathodal tDCS to the left dorsolateral prefrontal cortex (dlPFC) or sham tDCS in a crossover design. During tDCS, participants completed the alcohol approach implicit association test (IAT) and the drinking identity IAT, along with two control tasks. Additionally, we collected explicit ratings of the IAT stimuli and assessed craving before and after each experimental session. Preregistered ANOVAs revealed significant implicit alcohol-avoidance and non-drinking identity biases. Cathodal tDCS did not modulate IAT scores. Explicit ratings showed a preference for non-alcoholic drinks and non-drinking identity, correlating moderately with IAT scores. Exploratory analyses indicated that cathodal tDCS mitigated the increase in nicotine craving during the experimental session. This preregistered clinical trial provides robust evidence that single-session cathodal tDCS to the left dorsolateral prefrontal cortex does not modulate implicit associations in AUD, with Bayesian analyses corroborating the absence of tDCS effects. Our results emphasize the impact of contextual factors on the interplay between explicit and implicit cognitive processes and underscore the importance of investigating multisession stimulation paradigms in future research.