Studying Effects of Transcranial Alternating Current Stimulation on Hearing and Auditory Scene Analysis

Lars Riecke

Recent studies have shown that perceptual detection of near-threshold auditory events may depend on the timing of the event, relative to the phase of ongoing brain oscillations (i.e., periodic fluctuations in neural excitability). It has been further shown that transcranial alternating current stimulation (tACS), a non-invasive and silent brain stimulation technique, can entrain ongoing cortical alpha oscillations and thereby offer some experimental control over the phase of these oscillations. Based on these and related alpha-tACS findings, the present study investigates the potential of delta/theta-tACS to modulate hearing and auditory scene analysis in normally-hearing listeners. Detection performance is measured in silence or in a multi-tone background for near-threshold auditory stimuli that are modulated at 4Hz and presented at various moments (phase lags) during ongoing oscillatory electric stimulation (two synchronous 4-Hz alternating currents applied transcranially and simultaneously to the two cerebral hemispheres). Preliminary results indicate that performance fluctuates as a function of phase lag, and these fluctuations can be explained best by a sinusoid whose frequency matches that of the tACS. This suggests that tACS may amplify/attenuate sounds that are temporally coherent/anticoherent with it and thereby enhance/reduce their audibility.