The R3 component of the blink reflex in man: a reflex response induced by activation of high threshold cutaneous afferents.

Ten successive experiments were carried out in 10 volunteers to compare the physiological properties of R2 and R3 components of the blink reflex. The electrical activation threshold of the R3 component was found to be significantly higher than that of the R2 response and was more susceptible to anaesthetic blocking of the peripheral afferents. This result suggests that the R3 component is induced by the activation of a different population of peripheral afferents from the R2 component. A recovery cycle study performed using a double stimulus showed that R3 is inhibited to a greater extent and for a longer time than R2. The temporal relationship of R3 to the voluntarily produced blink demonstrates that R3 is not a voluntary response to electrical stimulation. In conclusion, these experiments support the existence of an independent R3 component and its relationship with the activation of small diameter and higher threshold afferent fibres, perhaps nociceptive ones.