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.