Transcranial infrared laser stimulation (TILS) refers to the use of infrared laser to photobiomodulate the human brain, which has been reported beneficial in enhancing human cognition. We previously investigated TILS-induced electrophysiological effects and observed increases of power density in alpha wave oscillation. However, clear association between the brain wave alteration and improvement of neural cognition is limited. Phase–amplitude coupling (PAC) is a recently proposed neural mechanism for coordinating information processing across brain regions. In this study, we wish to examine if TILS would create any enhanced PAC at particular frequency bands in particular brain regions. A 64-channel electroencephalography (EEG) system was employed to determine placebo-controlled, electrophysiological activities from 19 healthy human participants before, during and after TILS. After a 2-minute baseline, we applied a 1064-nm laser with a total power of 3.5 W on the right forehead of each human participant for 8 minutes, followed by a 3-minute recovery period. An EEG processing package (Brainstorm) was used to perform cross-frequency PAC analysis for each participant’s measurement, followed by group-level, paired T-tests between the placebo and TILS conditions. The statistical results showed that TILS induced significant inter-cerebral PAC among several brain oscillations, specifically (1) slow-delta (0.5-1 Hz) activity modulating both alpha band (8-11 Hz) and high gamma band (70-85 Hz) activities, and (2) alpha band (8-11 Hz) modulating high gamma band (70-85 Hz) activity. All of these results suggest that TILS is able to enhance thalamocortical, cortical-hippocampal-cortical, and hippocampal-thalamic activity, all of which lead to enhancement of human cognition.
|