Figure 1.

Experimental paradigm. Acupuncture needle manipulation was performed at LI 4 (arrow pointing to red dot) in the first interosseous muscle (gray shading). Scanning began 2 min prior to needle insertion. The needle was left at rest for 2 min before manipulation. Two epochs of needle manipulation (M1, M2) each lasting 2 min, were administered separated by a rest interval of 4 min. The needle was removed 2 min after M2. Scanning was continued for an additional 2 min. For statistical analyses, the mean signal intensity of the three periods of needle at rest (R1, R2, R3) served as the baseline for changes in signal intensity during needling. For the control experiments tactile stimulation was delivered to the skin surface overlying the acupuncture point with the tip of a flexible wire during M1 and M2. Total scanning time was 16 min.