Investigating the mechanisms of acupuncture on neural excitability in healthy adults

Acupuncture is gaining interest as a potential treatment modality for various neurological conditions. Yet, the underlying mechanisms and efficacy on brain function are not well understood. Therefore, this study investigated the previously proposed hypothesis that acupuncture suppresses motor cortex excitability using transcranial magnetic stimulation (TMS) in healthy adults. The study was randomised, sham-controlled, and double-blinded. Single and paired-pulse TMS was delivered before, during, immediately after, and 30 min after removal of the needle. Acupuncture to the right Hegu acupoint (LI-4) of the hand was delivered by an experienced acupuncturist using standardised manipulations. A disposable (0.22×30 mm, Hwato) needle was used for verum stimulation (penetrating) and a Park retractable needle for sham (nonpenetrating). The peak-to-peak amplitude of TMS-induced motor-evoked potentials was recorded from two intrinsic hand muscles. Needling sensations were quantified using the Massachusett's acupuncture sensation scale. Participant needling sensations were not different between verum or sham acupuncture (P>0.54). Corticomotor excitability, intracortical inhibition, and intracortical facilitation were not modulated by verum or sham acupuncture during, immediately after, or 30 min after, recorded from a local or distant hand muscle to the needling site (all P>0.075). Contrary to previous studies, manual acupuncture did not affect motor cortex excitability in healthy adults. Because of the increasing popularity of acupuncture therapy, further research using patient populations should be considered.