P 52 Amplitude modulation of the somatosensory alpha rhythm by transcranial alternating current stimulation applied at the individual endogenous frequency

Background/research question In a recent study we could demonstrate, that transcranial alternating current stimulation (tACS), applied at the individual somatosensory mu-alpha-frequency (mu-tACS), modulated somatosensory perception phasically. From other studies it is also known, that tACS, applied over visual areas may increase the amplitude of ongoing visual alpha oscillations. We therefore wanted to examine whether our behaviorally relevant mu-tACS protocol may also modulate somatosensory mu-alpha oscillations. Method For this purpose 23 participants (mean age: 27; 11 female) were tested in a combined tACS/EEG experiment with a randomized, single-blinded crossover design. Initially, each participant’s individual mu-alpha peak frequency was identified in a pre-experiment. Subsequently we applied two blocks of tACS (verum and sham, duration: 5 min) bilaterally over somatosensory areas, with a stimulation-free interval of five minutes between both blocks, while participants were watching a movie in silence and their EEG was recorded. For data analysis mu-alpha amplitudes two minutes before and two minutes after each stimulation block were extracted and compared between mu-tACS and sham. Results When comparing amplitude modulations of mu-alpha oscillations we found a significant difference between mu-tACS and sham with a significant decrease in amplitude after stimulation for the mu-tACS block but not for sham. This decrease in mu-alpha amplitude had a bilateral, central topography. Furthermore this modulation was specific for somatosensory mu-alpha-oscillations and not seen for visual alpha-oscillations. Discussion/Conclusion We here present electrophysiological evidence for a specific interaction between mu-tACS and somatosensory mu-alpha oscillations, supporting the functional specificity of tACS as an intervention method. However, the direction of modulation (amplitude decrease) was somehow unexpected, as an increase in amplitude of visual alpha oscillations during and after tACS over visual areas was reported in other studies. The difference may be related to potentially different characteristics of the modulated brain rhythm or the stimulation protocol and should be addressed in additional future studies.