Transcranial photobiomodulation increases functional connectivity and cortical excitability

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Abstract Submission 

Zhilin Li¹, Yiqing Hu¹, Yang Li¹, Chenguang Zhao¹, Zaixu Cui¹

¹Chinese Institute for Brain Research, Beijing, China

Zhilin Li  
Chinese Institute for Brain Research
Beijing, China

Yiqing Hu  
Chinese Institute for Brain Research
Beijing, China

Yang Li  
Chinese Institute for Brain Research
Beijing, China

Chenguang Zhao  
Chinese Institute for Brain Research
Beijing, China

Zaixu Cui  
Chinese Institute for Brain Research
Beijing, China

Transcranial photobiomodulation (tPBM), a promising noninvasive intervention, has been shown promising for modulating brain activity(Dmochowski et al. 2020; Song et al. 2020; Zhao et al. 2022). However, the mechanism underlying how tPBM modulates brain activity has not been systematically discussed(Dole et al. 2023). In the current study, we utilized the latest Transcranial Magnetic Stimulation(TMS) evoked potentials (TEP) and electroencephalogram(EEG) functional connectivity to shed light on this problem(Conde et al. 2019; Schoffelen and Gross 2009).

The study consisted of two experiments. In experiment I, data was collected from 75 subjects who were divided into three groups based on the frontoparietal(FP1/2) stimulation sites and wavelengths: 1) 1064 nm tPBM applied to the FP2, 2) 1064 nm tPBM applied to the FP1, 3) 852 nm applied to the FP2. To investigate the effect of tPBM on the brain network, all participants received a 12-minute non-invasive laser tPBM session, followed by an 8-minute EEG data acquisition to construct functional connectivity.
In experiment II, data were collected from 60 subjects divided into two groups based on wavelengths (1064 nm / 852nm). All participants received 12 minutes of laser tPBM at FP2 followed by 8 minutes of EEG acquisition with pulsed TMS at 0.2 Hz to calculate TEP, some of the 1064 nm group underwent the same protocol again after 24 hours. Both experiments mentioned above were double-blind and included a sham control group. The diode-pumped solid-state laser utilized in this study had a linewidth of ±1 nm. The laser beam was uniformly distributed and covered an area of 13.57 cm2 (4 cm in diameter), producing a continuous power output of 2271 mW. This resulted in a power density or irradiance of 167 mW/cm2(Zhao et al. 2022). The stimulation site in our experiment(FP1/2)was based on the 10-20 system used for EEG electrode placement.

The results of Experiment I indicate that the effects of tPBM on brain network modulation are site and wavelength-specific, with delayed effects observed(Fig 1). Specifically, when the stimulation site was FP2, only the wavelength of 1064 nm led to significant enhancement of functional connectivity. Although the number of functional connectivity enhancements in the 0-2 min period after the stimulation was low, it increased significantly in the 6-8 min period, becoming ten times more than in the 0-2 min period. Most of these enhancements were observed in the occipital-parietal and parietal-frontal lobes.
The findings from Experiment II indicate that tPBM has wavelength-specific and sustained effects on the modulation of neural activity(Fig 2). When a wavelength of 1064 nm was applied to FP2, a significant difference was found between the pre and post-stimulation TEP within the 0-100ms and 200-250ms after TMS pulse, and the significant difference at 200-250ms even lasted for up to 24 hours.

This study presents two experiments demonstrating that tPBM at 1064 nm on FP2 can modify brain activity and network patterns, with effects lasting up to 24 hours. By providing a systematic investigation of the modulation effect the tPBM applies to the brain, this study may be important in paving the way for developing and applying this promising neuromodulation technology.

Non-invasive Magnetic/TMS

TMS

Non-Invasive Stimulation Methods Other ¹

EEG/MEG Modeling and Analysis ²

Other - Transcranial photobiomodulation;Transcranial Magnetic Stimulation(TMS) evoked potentials (TEP);Functional connectivity;