Distinguishing acupuncture from placebo acupuncture has been a methodological challenge. We propose to use a quantitative brain imaging method to investigate the mechanism of acupuncture analgesia, placebo analgesia and their interrelationship. A well tested method to induce high and low expectation will be combined with acupuncture analgesia and sham acupuncture analgesia to create a 2 X 2 comparison of verum acupuncture and sham acupuncture each paired with positive and negative expectancies.