Transcranial photobiomodulation (tPBM) with near-infrared light on the human head has been shown to enhance human cognition. In this study, tPBM-induced effects on resting state brain networks were investigated using 111-channel functional near-infrared spectroscopy over the whole head. Measurements were collected with and without 8-minute tPBM in 19 adults. Functional connectivity (FC) and brain network metrics were quantified using Pearson’s correlation coefficients and graph theory analysis (GTA), respectively, for the periods of pre-, during, and post-tPBM. Our results revealed that tPBM (1) enhanced information processing speed and efficiency of the brain network, and (2) increased FC significantly in the frontal-parietal network, shedding light on a better understanding of tPBM effects on brain networks.

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.

When performing physical exercise, the contracting muscles elicit demand for oxygen, which is supplied by increased blood flow. The brain must register and simultaneously integrate input from feedforward (i.e., central command) and feedback (e.g., exercise pressor reflex) neural mechanisms to make necessary cardiovascular adjustments to meet the metabolic demand of the exercise.^1,2 During exercise involving the arms, peripheral fatigue sets in, as characterized by reduced force-generating capability of the muscles that subsequently evolves into central fatigue, resulting in decreased neural drive to the muscles, after prolonged physical activity.^{1 – 6} Central fatigue’s contribution to peripheral fatigue is less understood and functional brain imaging during fatiguing exercises is being investigated as a tool to help elucidate the underlying mechanisms.^{3 – 11} Neural pathways gradually alter their connectivity (neuroplasticity), which affects regulation of the cardiovascular system both at rest and during exercise. Physically active individuals exhibit exercise-related neuroplasticity and have improved cardiovascular health, whereas inactive individuals may be predisposed to higher incidences of cardiovascular disease.^1,5,12