Effects of acupuncture on somatosensory evoked potentials: a review.

Although acupuncture has a long history of analgesic effects, the mechanisms underlying its effects are still unclear. Somatosensory evoked potential (SEP) methodology has been adopted in the research of acupuncture since the 1970s. In research on the effects of acupuncture on the conventional SEP, variable results have been observed, and two different opinions concerning the presence or absence of acupuncture effects on the conventional SEP are discussed. Since the conventional SEP is mediated mainly by fast conducting sensory nerve fibers, the conventional SEP methodology, especially that for recording short-latency SEP, may be inadequate for studying acupuncture mechanisms. In the case of the long-latency cortical SEP, there are too few data available to judge the effects of acupuncture analgesia (AA). Studies on the effects of AA on pain SEPs demonstrated that AA has a suppressive effect on amplitude of the pain SEP (and affecting the latency as well in some experiments) in both animals and humans, being accompanied by increased pain threshold. Thus, acupuncture seems to have analgesic effects that are probably related to activation of the antinociceptive system, and application of the pain SEP methodology to the study of mechanisms of AA may be promising.