Significant Increases in EEG Anterior-Posterior Alpha and Beta Powers By Transcranial Photobiomodulation (tPBM) in Healthy Humans With Exclusion of Thermal Effects

Transcranial photobiomodulation (tPBM) of the prefrontal cortex can improve human cognition and increase electroencephalogram (EEG) alpha and beta powers, but it was unclear whether tPBM-induced heat would influence EEG oscillation powers. This study aimed to prove that tPBM-induced increases in anterior-posterior EEG powers at alpha and beta bands would be significant after removal of tPBM-associated thermal effects. We performed both sham-controlled tPBM and sham-controlled thermal stimulation (thermo_stim) experiments under the eyes-closed resting state with concurrent recordings of 64-channel EEG before, during, and after 8-min tPBM at 1064-nm wavelength and thermo_stim with temperature from 33 to 41 °C, respectively, from healthy humans (n=46 for tPBM; n=14 for thermo_stim). Sham-subtracted topographies of EEG powers at five frequency bands were averaged at the group level during and post both stimulations. Two-sample t-tests with FDR correction and effect size were calculated for comparing tPBM and thermal effects at all five frequency bands. Right-frontal tPBM induced significant increases in EEG anterior-posterior alpha and beta powers under the eyes-closed conditions, consistent with the results previously reported in the eyes-open tPBM experiments. In contrast, right-frontal thermal stimulation under the eyes-closed resting state resulted in opposite effects on EEG power patterns with respect to those by tPBM. tPBM-induced enhancement in alpha and beta oscillations occurred during the 8-min intervention after exclusion of thermal effects. The ability of tPBM to synchronize alpha and beta oscillations in the anterior-posterior regions may be linked to the enhancement of frontoparietal network and the improvement of human cognition.