Experimental Design. Each subjects received both true and sham acupuncture in a randomized order. Boxcar design of fMRI paradigm was used. Each fMRI paradigm lasted a total of 8 minutes and 40 seconds. Stimulation (true or sham acupuncture) was initiated at the time points indicated with the downward arrows and stopped at those indicated with the upward arrows (panel 1a). During true acupuncture, a real acupuncture needle was inserted at the LI-2 acupuncture point. During sham acupuncture, a Streitberger placebo needle was applied at a non-acupuncture (sham) point (panel 1b).