Latencies of chemically evoked discharges in human cutaneous nociceptors and of the concurrent subjective sensations.

Percutaneous recordings from single nociceptive A delta- and C-fibers have been performed from the superficial radial nerves of conscious human subjects. Nociceptors were tested with a chemical irritant substance, which induced a burning sensation when applied to the intact skin. A comparison of the onset of spike discharges in nociceptors and the onset of the subjective burning sensation indicated that under the conditions of our experiments summation of input from nociceptors is needed in order to induce pain sensations. In particular, our results indicate spatial summation.