Transcranial photobiomodulation with infrared laser increases power of brain oscillations

Non-invasive transcranial photobiomodulation with a 1064-nm laser (tPBM L1064 ) has been reported to improve human performance on cognitive tasks as well as locally upregulate cerebral oxygen metabolism and hemodynamics. However, it is unknown whether tPBM L1064 also modulates electrophysiology, and specifically neural oscillations, in the human brain. The hypothesis guiding this study was that tPBM L1064 of the right prefrontal cortex enhances neurophysiological rhythms at specific frequency bands in the human brain under resting conditions. To test this hypothesis, we recorded the 64-channel scalp electroencephalogram (EEG) before, during, and after the application of 11 minutes of 4-cm-diameter tPBM L1064 to the right forehead of human subjects (n=20) using a within-subject, sham-controlled design. Time-resolved scalp topographies of EEG power at five frequency bands were computed to examine tPBM L1064 -induced EEG power changes across the scalp. The results showed time-dependent, significant increases of EEG spectral powers at the alpha (8-13 Hz) and beta (13-30 Hz) bands at broad scalp regions, exhibiting a front-to-back pattern. The findings provide the first sham-controlled topographic mapping that tPBM L1064 increases the strength of electrophysiological oscillations (alpha and beta bands), while also shedding light on the mechanisms of tPBM in the human brain.