Repetitive Gamma-tACS Improves Visuospatial Working Memory in Healthy Young Adults: A Randomized Study

In a single blind placebo controlled study, 35 healthy young adults were randomly assigned to three sessions of either active γ-tACS (n=18) or passive sham γ-tACS (n=17), to test the short-term and long-term efficacy of γ-tACS over the left DLPFC to improve visuospatial working memory performance in the spatial capacity delayed response task (SCDRT). The design allowed to evaluate the influence of stimulation protocol (active vs. sham), session of stimulation (day 1 to 3), session block (before stimulation, during stimulation and after stimulation) and VSWM retention load (1, 3, 5 or 7 stimuli). Active γ-tACS selectively improved VSWM performance in day 2 and 3, and the effect was greater following stimulation rather than during stimulation. Significant effects concerned response speed but not accuracy. VSWM performance gains of Active γ-tACS were no longer present long-term, at a follow-up session after two weeks. The present study provides novel evidence for a selective improvement in VSWM performance with three repeated sessions of γ-tACS in young adults, through entrainment of gamma rhythms in the left DLPFC.