Fig. 4.

Effects of TILS on EEG power spectral density (PSD) normalized by the power within the bandwidth of 0–50 Hz before (pre, blue curve), during (laser, green) and after (post, red) stimulation. The integral of PSD in each bandwidth is the relative power of the signal within that bandwidth. This power times epoch duration time gives the energy of the signal within that bandwidth (10 epochs of 1-min each for pre, laser and post recording periods). There were clear bilateral enhancements of alpha power in the occipital recordings (peaks around 10 Hz for alpha). The alpha power increased progressively from frontal, to parietal, to occipital recordings during laser and post-laser relative to pre-laser. No alpha effects were found in temporal recordings, which instead showed increased gamma power (32+ Hz) and beta power around 20 Hz