24. Effect of transcranial alternating stimulation (tACS) on the spontaneous EEG

Transcranial Direct Current Stimulation is a non-invasive method to modulate cortical excitability, depolarizing or hyperpolarizing neurons, by continuous (c-tDCS), oscillatory (so-tDCS) or alternating current (tACS). We used the tACS (<1 mA, 0.8–5 Hz for 10 min) to actively induce changes in electrophysiological measures of sleepiness. Waking EEG was recorded from 28 derivations before and after tACS stimulation in 10 subjects for the tACS and sham (control). Mean EEG power was calculated for the following bands: delta (1– 4 Hz), theta (5–7 Hz), alpha (8–12 Hz), beta1 (13–15 Hz) and beta2 (16–24 Hz). The two conditions (active vs. sham), for each band and for each derivation, were compared by t-tests, and corrected for multiple comparisons. In the eyes-closed condition, the results point to an increase in delta activity at the frontal area after tACS at 0.8 Hz frequency. In the eye-open condition, the increased delta activity was confirmed at the right temporal area after tACS at 5 Hz, while an decrease of beta1 activity was found at the right parietal area after tACS at 0.8 Hz. According to the a priori hypothesis, tACS affects spontaneous EEG activity in both conditions (i.e., eyesclosed and open), because it mainly facilitates the increase i