Abstract
Objective: Transcranial Photobiomodulation (tPBM) provides a safe and noninvasive brain stimulation to intervene with brain functions. Despite the large body of reported clinical and behavioral outcomes, there is still need for a fuller understanding regarding NIR penetration and mechanisms. In this study, we investigated the effect of tPBM on cortical oscillations using power spectrum analysis.
Methods: Twenty five healthy volunteers (9M/16F; mean age ± SD= 68.3± 6.63 years) received 20 minutes of active tPBM using 810 nm light-emitting diodes(LEDs), pulsed at 10 Hz with 50% duty cycle. In a randomized cross-over design, all participants received four arms of stimulation: (1) active (standard montage; LEDs irradiating the 4 hubs of default mode network), (2) active (non-standard montage - rearrangement of LEDs over right temporal-occipital regions, (3) active intranasal diode only, (4) sham (standard montage). Resting state EEG data was collected 10 minutes before (pre-tPBM), and at 10 and 30 minutes after (post10-tPBM; post30-tPBM) each stimulation session. The artifact-free resting-state data were used for power spectrum analysis.
Results: Our power spectrum analysis showed significant changes in most frequency bands with all active stimulations (P<0.01). However, this modulation depended on the type and the location of stimulation. Namely, in type (1), a significant increase in theta, alpha, beta and gamma both post10-tPBM and post30-tPBM. For type (2), we found a significant increase in theta post30-tPBM, and alpha both post10 and post30-tPBM. For type (3) we found a significant increase in beta and gamma post10-tPBM and post30-tPBM, prominent in the posterior channels. Type (4) showed no significant change in any frequency bands.
Conclusion: Findings from this study provide novel evidence that tPBM modulates neural oscillations in a frequency and location dependent manner. This is also the first investigation to measure the significant effect of an intranasal NIR LED on brain oscillation with EEG.
Keywords: tPBM, EEG, power spectrum, cortical oscillation
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