PAIN-EVOKED POTENTIALS - WHAT DO THEY REALLY MEASURE

Cerebral evoked potentials (EPs) in response to painful stimuli have b een recorded since the 1970s. Based on the apparent relationship of th e response amplitude to intensity of stimulation, these potentials are conventionally interpreted as reflecting the sensory-discriminative a spects of pain. As such, pain-EPs provide an objective measure for sen sation of pain. An alternative interpretation regards the pain-EP as c omprised of al least two overlapping components, one pain-specific, th e other, a P300 wave. In the case of pain, the P300 may reflect the de gree of discomfort or unpleasantness, thus reflecting the emotional-mo tivational aspect. To establish the nature of the pain-EP, mini doses of a benzodiazepine, counterbalanced with placebo, were given to 6 nor mal volunteers. Benzodiazepines decrease anxiety, and so diminish the emotional response to pain, but they have no analgesic effect. In all subjects, pain perception was unchanged, while the EP wave was almost completely obliterated. We conclude that the pain-EP reflects the emot ional-motivational response to pain rather than the sensory-discrimina tive. Thus, it provides a useful neurophysiological tool for studying the emotions associated with pain.