Experiment 3 further examined the relationship between working memory and the timing of frontotemporal network dynamics (see Methods for details). In brief, we found that antiphase HD-tACS, designed to desynchronize cortical interactions between frontotemporal areas, rapidly induced working memory deficits in younger adults (Supplementary Fig. 2). The results across Experiments 1–3 suggest that by changing the phase angle of stimulation (inphase versus antiphase) we can change the direction of the causal effects on performance (improvement versus impairment). Finally, in Experiment 4, we sought to extend the stimulation benefits induced in older adults in Experiment 1 to poor performing younger subjects (see Methods for details and Supplementary Fig. 3). The results from Experiment 4 suggest that the HD-tACS improvement may be applicable to a wide range of individuals who exhibit suboptimal working memory function and reductions in synchronous neural activity.
