Exploring the CNS effects of acupuncture needling with TMS

CNS-effects of acupuncture are still a matter of debate. Until now, neurophysiological studies using proper placebo conditions are scarce. CNS excitability can be determined by transcranial magnetic stimulation (TMS) using the motor cortex as a reference region. Aim: The aim of the present study was to explore short term effects of manual acupuncture needling on motor cortex excitability with TMS while controlling for non-specific effects of needle insertion by using a single-blind, non-penetrating state-of-the-art sham condition (“Streitberger Needle”). Methods: Distinct variants of motor cortex excitability such as resting motor threshold (rMT), active motor threshold (aMT), cortical silent period (CSP), short intra-cortical inhibition (SICI) and intra-cortical facilitation (ICF), were assessed before and after needling in healthy volunteers from the abductor digiti minimi of both hands. Both verum acupuncture and sham acupuncture with retractable tips were performed for 200 seconds at a standard acupoint near the right knee. Results: Verum compared to sham acupuncture needling was found to significantly decrease motor cortex excitability as represented by increased rMT. No significant effect of needling was found for all other parameters tested (aMT, CSP, SICI or ICF). Conclusion: Our results suggest a specific inhibitory effect of deep manual acupuncture on the excitability of the motor system, potentially relevant for the proposed therapeutic effects of acupuncture.