Prolonged hypalgesia following “acupuncture” in monkeys

After learning to escape painful electrical stimulation of one leg, Cebus albifrons monkeys were presented with a random schedule of five intensities, and they consistently responded with minimal latencies to the higher intensities during control sessions. Preceding different sets of experimental sessions, the monkeys received mild electrical stimulation between loci below the knees that were intended to correspond to acupuncture points. following the majority of these “acupuncture treatments” significant elevations of escape latencies were observed at the higher stimulus intensities. The decreased reactivities to noxious stimuli were often delayed in onset following the end of “acupuncture treatments,” and substantial alterations of escape behavior were detected up to 70 hours post-treatment. Regardless of the relevance of this finding to acupuncture, it represents an unusually enduring alteration of pain sensitivity following stimulation of the body surface in a situation free from suggestive influences.