Dose-response of Transcranial Photobiomodulation on Resting-State EEG Dynamics

Transcranial photobiomodulation (tPBM) is a novel and non-invasive brain stimulation technique for promising cognitive improvement. yet the mechanisms underlying its modulation of human brain function remain unclear. In this study, three double-blind sham-controlled experiments were conducted to investigate the effects of tPBM irradiance, duration, and total energy on neural dynamics. We recorded electroencephalography (EEG) of 101 adults during tPBM intervention and assessed EEG power, individual alpha peak frequency (IAPF), and weighted phase lag index (wPLI) to explore the underlying mechanisms. Results revealed that moderate doses of tPBM delayed the decline in parietal-occipital IAPF, whereas higher irradiance enhanced the whole-brain connectivity indexed by wPLI. Our study provides consistent evidence across three experiments that the effects of tPBM on human neural dynamics are dose-dependent: moderate doses of tPBM resulted in regional IAPF stabilization linked to alertness, whereas higher irradiance led to global effects that increased the functional connectivity associated with brain integration. This dose-response duality highlights the importance of tailoring tPBM parameters to optimize therapeutic outcomes.