Clinical trials testing the analgesic (pain-relieving) effects of acupuncture often find that actual (verum) and sham (placebo) acupuncture have similar analgesic effects. Basic science research also suggests that acupuncture and placebo may share some analgesic mechanisms in the brain. A recent NCCAM-funded study used functional magnetic resonance imaging (fMRI) to investigate whether acupuncture and placebo analgesia work through the same brain networks, and how an individual's expectation of pain relief is involved in the process. The study was conducted by researchers affiliated with Massachusetts General Hospital, the Osher Research Center at Harvard Medical School, and the University of Hull in the United Kingdom.
In the study, 48 people were divided into 4 groups based on treatment mode (actual or sham acupuncture) and expectation of pain relief (high or low). In actual electroacupuncture, an electric current passed through needles inserted into the skin; in sham treatment, the needles did not penetrate the skin and there was no electrical stimulation. Experimental conditions were manipulated to control expectation.
Before and after treatment, the subjects were exposed to heat stimuli. They rated the level of pain they experienced and underwent fMRI scans to measure brain activity. Analysis of data for high-expectation subjects found that although the actual and sham groups reported similar levels of pain relief, fMRI images showed different patterns of brain activity for the two groups. In addition to affecting regions of the brain that process pain, actual acupuncture appears to modulate nerve pathways that descend from the brain to the spinal cord, inhibiting the transmission of pain signals in the spinal cord. Expectation appears to enhance acupuncture analgesia by activating parts of the brain involved in affective modulation—regulating the subjective experience of pain.
The researchers concluded that their findings provide evidence of different underlying mechanisms for acupuncture and placebo analgesia. They also suggest that expectation can significantly enhance the analgesic effect of acupuncture.
Kong J, Kaptchuk TJ, Polich G, et al. Expectancy and treatment interactions: a dissociation between acupuncture analgesia and expectancy evoked placebo analgesia. NeuroImage.; 45(3):940–949.2009