Age-related changes in excitability of nociceptive flexion reflex. An electrophysiological study in school-age children and young adults.

By stimulating the sural nerve at the retromalleolar level and recording EMG response from biceps femoris muscle two components can be evoked: RII (shorter latency, lower threshold, non-nociceptive) and RIII (longer latency, higher threshold, nociceptive). RIII reflex represents a useful tool for pain research in humans since a close correlation exists between the reflex threshold and that of pain. In our study, latency, amplitude, duration and threshold of RII and RIII reflexes were investigated in school-age children (aged 7-14 years) and young adults. RIII threshold was significantly lowered in children, while the other parameters were similar in both groups. Our data suggest the existence of a reduced inhibitory descending control in nociceptive spinal neurones in children.