Effects of acupuncture needle penetration on motor system excitability

Transcranial magnetic stimulation (TMS) studies reported changes in motor evoked potential amplitude after acupuncture needling both at traditional acupoints and non-acupoints. However, the effects of needle penetration per se have not yet been investigated with TMS. The present study aimed at exploring effects of deep manual acupuncture needling compared to a state-of-the-art, non-penetrating control condition on several standard TMS measures of motor system excitability.

Twenty healthy volunteers received both verum and sham acupuncture applied at the acupoint GB 34 near the right knee, using a crossover design. A needle with a retractable tip ("Streitberger needle") was used as sham condition to minimize non-specific effects. TMS parameters (resting motor threshold, active motor threshold, cortical silent period, short intracortical inhibition, and intracortical facilitation) were calculated from the abductor digiti minimi (ADM) of both hands 15 min before and after needling by a researcher blind to the treatment condition.

Verum compared to sham acupuncture significantly increased resting motor threshold. No significant treatment effect was found for any other measure, though cortical silent period and intracortical facilitation showed trends to increase in the hemisphere contralateral to the needling site after verum acupuncture.

These results suggest a subtle but specific inhibitory effect of acupuncture needle penetration at acupoint GB 34 on motor system excitability. Further investigations should be performed with a particular emphasis on the measurements of resting motor threshold, cortical silent periods and intracortical facilitation.