The neural mechanism underlying the analgesic effect of acupuncture is largely unknown. We aimed at investigating the effect of abdominal acupuncture (AA) on the laser evoked potential (LEP) amplitude and laser-pain rating to stimulation of body parts either homotopic or heterotopic to the treated acupoint.
LEPs were recorded from 13 healthy subjects to stimulation of the right wrist (RW), left wrist (LW), and right foot (RF). LEPs were obtained before, during, and after the AA stimulation of an abdominal area corresponding to the representation of the right wrist. Subjective laser-pain rating was collected after each LEP recording.
The amplitude of the N2/P2 LEP component was significantly reduced during AA and 15 minutes after needle removal to both RW (F=4.14, p=0.02) and LW (F=5.48, p=0.008) stimulation, while the N2/P2 amplitude to RF stimulation (F=0.94, p=0.4) remained unchanged. Laser-pain rating was reduced during AA and 15 minutes after needle removal only to RW stimulation (F=5.67, p=0.007).
Our findings showing an AA effect on LEP components to both the ipsilateral and contralateral region homotopic to the treated area, without any LEP change to stimulation of a heterotopic region, suggest that the AA analgesia is mediated by a segmental spinal mechanism.

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