4-Hz Transcranial Alternating Current Stimulation Phase Modulates Hearing

Background: Non-invasive brain stimulation with transcranial alternating currents (tACS) has been shown to entrain slow cortical oscillations and thereby influence various aspects of visual perception. Much less is known about its potential effects on auditory perception. Objective: In the present study, we apply a novel variant that enables near-equivalent stimulation of both auditory cortices to investigate the causal role of the phase of 4-Hzcortical oscillations for auditory perception. Methods: We measured detection performance for near-threshold auditory stimuli (4-Hz click trains) that were presented at various moments during ongoing tACS (two synchronous 4-Hz alternating currents applied transcranially to the two cerebral hemispheres). Results: We found that changes in the relative timing of acoustic and electric stimulation cause corresponding perceptual changes that oscillate predominantly at the 4-Hz frequency of the electric stimulation, which is consistent with previous results based on 10-Hz tACS. Conclusion: TACS at various frequencies can affect auditory perception. Together with converging previous results based on acoustic stimulation (rather than tACS), this finding implies that fundamental aspects of auditory cognition are mediated by the temporal coherence of sound-induced cortical activity with ongoing cortical oscillations at multiple time scales. (C) 2015 Elsevier Inc. All rights reserved.