We combined tACS with MEG recordings to directly test the causal role of local alpha oscillations in visual spatial attention. After stimulating occipital cortex in one hemisphere for 15min we used evoked responses to evaluate the effects of alpha entrainment on the attentional weighting of visual input (dot probes). Our data describe in detail the spatial specificity as well as the exact time course of lasting rhythmic entrainment in early visual cortex. By analyzing both phase and power spectra of the entrained rhythms we show how experimentally induced alpha rhythms lead to lasting inhibition and, in consequence, to suppressed visual responses. The specific stimulation setup and additional control experiments rule out alternative possibilities of stimulation effects by retinal activation, proving that it is the actual (direct) entrainment of extrastriate cortex the leads to attentional weighting.

Meeting abstract presented at VSS 2016