Laser acupuncture improves cortical excitability and behavioural performance in healthy individuals: a randomized controlled trial

This pioneering study investigated the effects of laser acupuncture (LA) on corticospinal excitability and behavioral performance in healthy adults, using a rigorous methodological approach that combines transcranial magnetic stimulation (TMS) with behavioral measures. The research fills an important gap in knowledge about the neurobiological mechanisms of LA, a noninvasive modality that uses low-intensity laser radiation at acupoints. The study employed a randomized, placebo-controlled, single-blind crossover design involving 18 right-handed healthy participants who completed four experimental sessions. Each participant received LA at three points of the Large Intestine meridian — LI-4 (Hegu, 合谷), LI-10 (Shousanli, 手三里), and LI-11 (Quchi, 曲池) — in addition to a control session with placebo laser.

The choice of these points was based on a previous meta-analysis identifying their relevance to motor function and their innervation by the radial and median nerves, corresponding to spinal segments C5–C8. The protocol used a gallium aluminum arsenide laser (655 nm, 50 mW) for 5 minutes per point, with a total dose of 7.5 J per session. Neurobiological measures included assessment of corticospinal excitability via motor evoked potential (MEP) amplitude, along with paired-pulse protocols to quantify short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI), and intracortical facilitation (ICF). These measures provide insight into the underlying GABAergic and glutamatergic mechanisms.

Behavioral performance was assessed through the Purdue Pegboard test for manual dexterity and computerized reaction-time tasks via PsyToolkit. Results demonstrated that LA at LI-4 and LI-10 produced significant increases in corticospinal excitability compared with baseline and placebo conditions (p < 0.01), whereas LI-11 showed only a non-significant trend. Analyses of intracortical circuits revealed that LI-4 and LI-10 reduced GABAergic inhibition (SICI and LICI) and increased glutamatergic facilitation (ICF), suggesting modulation of inhibitory and excitatory systems. Behaviorally, LI-4 significantly improved reaction time (p < 0.05), whereas LI-10 showed immediate post-intervention effects.

Analysis of individual factors revealed that participant expectation was a significant predictor of response to LA (p < 0.034), highlighting the importance of top-down cognitive mechanisms in neuroplasticity. The clinical implications are substantial, since LA offers distinct advantages over traditional acupuncture: painless application, shorter sessions, minimal adverse events, and greater capacity for experimental blinding. The proposed mechanisms involve photobiomodulation through mitochondrial ATP production, reduction of inflammation, and improvement of microcirculation. Limitations include the population of young healthy adults, which may show ceiling effects limiting detectable improvements, assessment only of immediate effects without long-term follow-up, and a single-blind design.

The study establishes neurobiological foundations for LA as a neuromodulation technique, with point specificity evidenced by the different response profiles among LI-4, LI-10, and LI-11 despite their belonging to the same meridian.