Phase-dependent oscillatory dynamics during needle retention and withdrawal: a comparison of penetrating and non-penetrating acupuncture.

Introduction: Clinical and neuroimaging studies have shown that non-penetrating sham acupuncture can elicit effects comparable to those of verum acupuncture. However, the electrophysiological signatures on the scalp remain unclear. Method: In a 2 × 2 crossover study involving 20 acupuncture-naive college students, we recorded electroencephalography (EEG) during verum and sham acupuncture at Hegu (LI4) to determine whether sham acupuncture evokes scalp electrophysiological activities comparable to verum acupuncture during the needle retention and post-withdrawal phases. Results: Despite eliciting a stronger deqi sensation, verum acupuncture produced scalp electrophysiological responses that closely resembled those evoked by sham acupuncture. Both interventions were associated with a significant increase in theta power in the central region during the needle retention and post-withdrawal phases, a significant increase in beta power in the central region during the needle retention phase, and a widespread reduction in alpha power from the needle retention to the post-withdrawal phase. Nevertheless, sham acupuncture may exert a relatively weaker influence, and the most consistent difference between verum and sham acupuncture concerned the alpha power reduction from the needle retention phase to the post-withdrawal phase. Exploratory correlation analyses indicated that the associations between deqi sensations and scalp EEG power may differ between verum and sham acupuncture. Conclusion: These results indicate that non-penetrating skin touch stimulation at acupoints and the associated sensory attention can trigger electrophysiological activities similar to, though partially weaker than, those of verum acupuncture.