Cerebral slow waves related to the perception of pain in man

Significant amplitude and temporal augmentation occurred in later time segments of human somatosensory evoked responses (60–700 ms) when percutaneous electrical pulse stimulation, delivered to finger, toe, or lip, indicated subjectively both crossing of a perceptual pain threshold and somatotopic movement associated with a noxious, qualitative change. Sequential pseudorandomizing of stimulus intensity (noxious and nonnoxious) or modality (contingent acoustic clicks) suggested that the waveform changes represented, at least in part, stimulus-specific information due to differential activation of peripheral fiber systems, rather than stimulus-nonspecific processing of event significances. The late waves were localizable, on scalp, to parietal and vertex regions, with insignificant contralateralization for finger stimuli. Their augmentation was related to subjective reports rather than to physical stimulus parameters, confirming previous data on potentially noxious mechanical stimulation of digits and palm, and another laboratory's noxious stimulation of tooth pulp. Subsequent data from a third laboratory, resulting from noxious laser stimulation of forearm, have replicated this late, slow-wave activity.