Optimized stimulation and recording parameters of human ‘nociception specific’ blink reflex recordings

Objective: Few non-invasive methods are available for studying trigeminal nociception in humans. The ‘nociception specific’ blink reflex (nBR) is elicited by a preferential stimulation of trigeminal nociceptive fibers and is highly sensitive to changes in trigeminal nociception. The aim of this study was to establish its optimal stimulation parameters. Methods: The inter-individual variability of R2 responses (41 healthy subjects), symmetry of R2 responses after right vs. left sided stimulation (25 subjects), optimal stimulation parameters (3 groups, each 16 subjects) and re-test reliability over time (15 subjects) were studied. Results: The nBR had a R2 response with a latency of 44.7±7.3 ms, but no R1 response. The mean difference of R2 latencies (right vs. left sided stimulation) was 0.4±2.1(SD) ms, the mean ratio of the R2 response areas (RA) was 1.05±0.39 (SD). Thus, lateral differences of onset latencies greater than 4.6 ms (0.4+4.2 (2SD)) or >1.83-fold (1.05+0.78 (2SD)) of RA can be assumed as outside of normal range. Long inter-block intervals of 7 min minimized the cumulative habituation of R2 RAs to 23%, onset latencies remained constant. Re-test reliability over 4 weeks was high both for latencies (Crohnbachʹs ALPHA=0.85) and RAs (alpha=0.94). Conclusions: The nBR with the established stimulation parameters could be used for studying trigeminal nociception.