Transcranial photobiomodulation and thermal stimulation induce distinct topographies of EEG alpha and beta power changes in healthy humans

Abstract

Our 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 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 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 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) tPBM vs light-stimulation sham, (2) thermo_stim vs heat-stimulation sham, and (3) 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) tPBM significantly increased EEG alpha and beta powers, (2) the thermal stimulation created opposite effects on EEG power topographic patterns, and (3) 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 tPBM.

Combination of Group Singular Value Decomposition and eLORETA Identifies Human EEG Networks and Responses to Transcranial Photobiomodulation

“…With the same inclusion and exclusion criteria as those in our previous studies ( Wang et al, 2016 , 2018 , 2021 ), a total of 49 healthy human subjects were recruited (19 females of 27.4 ± 6.1 years of age; 30 males of 28.7 ± 4.7 years of age) from the local community of the University of Texas at Arlington for participating this study. The experimental protocol was approved by the institutional review board (IRB) at the University of Texas at Arlington and complied with all applicable federal and NIH guidelines.…”

“…The sham-controlled experimental protocol was reported earlier ( Wang et al, 2021 ) but briefly shown in Figure 1 . Each tPBM or sham experiment took a total of 13 min, ranging from −2 min to 11 min, with a 2-min baseline, an 8-min tPBM/sham, and a 3-min recovery period.…”

“…Most of these studies have reported alterations of electroencephalography (EEG) powers by tPBM compared to sham stimulation. In particular, our group recently observed that tPBM enabled to neuromodulate the eyes-closed, task-free human brain, causing increases of EEG alpha and beta powers with significantly distinct topographies compared to those under sham and thermal stimulations ( Wang et al, 2021 ). However, these approaches would not permit spatial identification of brain networks and/or functional connectivity being activated or photo-modulated by given tPBM.…”

Red Light Optogenetics in Neuroscience

“…The mechanisms of PBM are still under debate, but are possibly related to mitochondrial enzymes, the production of reactive oxygen species, and endogenous red light-sensing proteins ( Hamblin, 2016 ). Outside of different survival pathways, transcranial PBM has been shown to modulate neural activity, which was apparent through changes in electroencephalography (EEG) even in humans ( Zomorrodi et al, 2019 ; Wang et al, 2021 ). To summarize, the effects of both endogenous opsin activity (induced by blue light) and PBM (induced by red light) need to be considered in each study.…”

Distinct spatio-temporal and spectral brain patterns for different thermal stimuli perception

“…The study concluded that neural responses in different EEG frequency bands were sensitive to different factors when thermally stimulating subjects’ hands. Furthermore, the study by Wang et al 21 studied changes in EEG rhythms, after laser-induced heat thermal stimulation of 33–41 C. The authors reported a decrease in EEG power topographic patterns as a result of the laser-induced heat stimulation. In another study by Breton et al 22 , they focused on power modulation of different oscillatory components and its sensitivity to thermal comfort variations using EEG recordings.…”