Is the R3 component of the human blink reflex nociceptive in origin?

The R3 component of the blink reflex can reproducibly be evoked by noxious stimulation but can probably also be elicited by innocuous stimuli. This st udy was conducted to investigate the contribution of nociceptive A delta an d C fibers to the generation of the electrically evoked R3 blink reflex. El ectrical thresholds for detection. pain and all blink reflex components wer e determined and the modulatory effects of local anesthesia were investigat ed. The electrical R3 threshold of 4.6 +/- 0.5 mA (mean +/- SE) corresponde d to 2.9 times the detection threshold and to 0.35 times the pain threshold . The R3 threshold was significantly below the pain threshold. Under local anesthesia of the supraorbital skin with a complete loss of warm and cold s ensation, a loss of pinprick sensation. but a normal detection of tactile s timuli, the electrical pain threshold increased, all other thresholds remai ned unchanged. Under local anesthesia none of the reflex components were si gnificantly reduced. Cutaneous A beta fibers and nociceptive A delta fibers , but not unmyelinated C fibers, contribute to the generation of the electr ically evoked R3 component. According to the recruitment order in periphera l sensory nerves the electrical threshold of the R3 is mainly determined by activation of A beta fibers. Thus, it can nor be assumed that the electric ally evoked R3 is an adequate model to investigate nociceptive processing. (C) 2001 International Association for the Study of Pain. Published by Else vier Science B.V. All rights reserved.