Auditory and somatosensory evoked potentials in Friedrich's ataxia (FA)

Methodological considerations on the use of the blink reflex R3 component in the assessment of pain in man

We define the principal physiological properties of the nociceptive component R3 of the blink reflex (b.r.) on electrical stimulation of the supraorbital nerve, with the aim of supplying some rules for its use in the analysis of pain in man. We explore the relationship between the threshold (th) of R3 and that of pain on stimulation of the trigeminal nerve and the extent to which R3 is modulated by habituation and attentional levels. Both pain th and R3 th correlate significantly with age. The R3 th was always higher than the R2 th. Habituation definitely decreases the amplitude of R3, which easily disappears. Focusing of attention on the stimulus sharply inhibits R3 while distraction increases it. Our findings emphasize the need to take all these aspects into account when designing protocols for the study of pain mechanisms based on the R3 reflex component.

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.