This study aims to investigate the frequency-dependent effects of near-infrared (NIR) transcranial photobiomodulation (tPBM) on human cortical excitability and fine motor performance. A cohort of 20 healthy adult volunteers (aged 18-35 years) will participate in a randomized, double-blind, sham-controlled, single-center study utilizing a within-subject, five-arm crossover design. Each participant will undergo five distinct experimental conditions separated by a strict washout period: active Continuous Wave (CW) tPBM, active pulsed tPBM at three neural oscillation frequencies (10 Hz, 40 Hz, and 100 Hz), and an inactive Sham comparator. All interventions will be delivered using a clinical-grade near-infrared device. To isolate the specific effects of pulse frequency from overall energy delivery, the total energy dose (cumulative Joules) and total exposure time will be held perfectly constant across all active arms. The pulsed conditions will keeps the average irradiance and cumulative fluence identical to the continuous wave mode. Cortical excitability will be assessed via single- and paired-pulse Transcranial Magnetic Stimulation (TMS) protocols over the primary motor cortex (M1). Fine motor performance will be quantified using a smartphone-based Finger Tapping Test (FTT). Safety and systemic parameters will be tracked using the Systematic Assessment for Treatment Emergent Events - Systematic Inquiry (SAFTEE-SI) and vital signs. The central hypothesis is that distinct modulation frequencies will differentially influence corticospinal excitability and motor execution, independent of the total energy delivered.
Age range
18 Years – 35 Years
Sex
ALL
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Motor Evoked Potential (MEP) Amplitude - TMS
Timeframe: Immediately before the intervention (pre-intervention) and 20 minutes after the intervention (post-intervention)
Intracortical Facilitation (ICF) - TMS
Timeframe: Immediately before the intervention (pre-intervention) and 20 minutes after the intervention (post-intervention)
Short-Interval Intracortical Inhibition (SICI) - TMS
Timeframe: Immediately before the intervention (pre-intervention) and 20 minutes after the intervention (post-intervention)
Cortical Silent Period (CSP) - TMS
Timeframe: Immediately before the intervention (pre-intervention) and 20 minutes after the intervention (post-intervention)