Transcranial Photobiomodulation Enables Significant Changes in EEG Rhythms

Transcranial Photobiomodulation Enables Significant Changes in EEG Rhythms

A recent study demonstrated that prefrontal transcranial photobiomodulation (tPBM) with 1064-nm laser enables significant changes in EEG rhythms, but these changes might result from the laser-induced heat rather than transcranial photobiomodulation (tPBM). This study hypothesized that tPBM-induced and heat-induced alterations in EEG power topography were significantly distinct. We performed two sets of measurements from two separate groups of healthy humans under transcranial photobiomodulation (tPBM) (n = 46) and thermal stimulation (thermo_stim; n = 11) conditions.

Each group participated in the study twice under true and respective sham stimulation with concurrent recordings of 64-channel EEG before, during, and after 8-min transcranial photobiomodulation (tPBM) at 1064 nm or thermo_stim with temperature of 33–41 °C, respectively.

After data preprocessing, EEG power spectral densities (PSD) per channel per subject were quantified and normalized by respective baseline PSD to remove the power-law effect.

At the group level for each group, percent changes of EEG powers per channel were statistically compared between (1) transcranial photobiomodulation (tPBM) vs light-stimulation sham, (2) thermo_stim vs heat-stimulation sham, and (3) transcranial photobiomodulation (tPBM) vs thermo_stim after sham exclusion at five frequency bands using the non-parametric permutation tests.

By performing the false discovery rate correction for multi-channel comparisons, we showed by EEG power change topographies that (1) transcranial photobiomodulation (tPBM) significantly increased EEG alpha and beta powers, (2) the thermal stimulation created opposite effects on EEG power topographic patterns, and (3) transcranial photobiomodulation (tPBM) and thermal stimulations induced significantly different topographies of changes in EEG alpha and beta power.

Overall, this study provided evidence to support our hypothesis, showing that the laser-induced heat on the human forehead is not a mechanistic source causing increases in EEG power during and after transcranial photobiomodulation (tPBM).

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