Objective: The aims of the study were to test the short-term and long-term efficacy of repetitive γ-tACS over the left DLPFC to improve visuospatial working memory performance in the spatial capacity delayed response task (SCDRT). Methods: 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) The design allowed us to evaluate the influence of the stimulation protocol (active vs. sham), the stimulation session number (day 1 to 3), the session block (before stimulation, during stimulation and after stimulation) and the VSWM retention load (1, 3, 5 or 7 stimuli) on the response speed and accuracy. Results: Active γ-tACS selectively improved VSWM performance on day 2 and 3, and the effect was greater following stimulation rather than during stimulation. Significant effects were seen concerning response speed but not accuracy. The VSWM performance gains of the active γ-tACS were no longer present in the long-term at a follow-up session after two weeks. Conclusions: The present study provides novel evidence for a selective improvement in VSWM performance with three repeated sessions of γ-tACS in young adults through the entrainment of gamma rhythms in the left DLPFC.

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.