TDCS modulates working memory maintenance processes in healthy individuals

BackgroundThe effects of tDCS at the prefrontal cortex are often investigated using cognitive paradigms, particularly working memory tasks. However, the neural basis for the neuromodulatory cognitive effects of tDCS, including which subprocesses are affected by stimulation, is not completely understood. AimsWe investigated the effects of tDCS on working memory task-related spectral activity during and after tDCS to gain better insights into the neurophysiological changes associated with stimulation. MethodsWe reanalysed data from 100 healthy participants grouped by allocation to receive either Sham (0 mA, 0.016 mA, and 0.034 mA) or Active (1 mA or 2 mA) stimulation during a 3-back task. Electroencephalography (EEG) data was used to analyse event-related spectral power in frequency bands associated with working memory performance. ResultsFrontal theta event-related synchronisation (ERS) was significantly reduced post-tDCS in the active group. Participants receiving active tDCS had slower response times following tDCS compared to Sham, suggesting interference with practice effects associated with task repetition. Theta ERS was not significantly correlated with response times or accuracy. ConclusionstDCS reduced frontal theta ERS post-stimulation, suggesting a selective disruption to working memory cognitive control and maintenance processes. These findings suggest that tDCS selectively affects specific subprocesses during working memory, which may explain heterogenous behavioural effects.