The structure of the spike train coding the nociceptive signal was investigated by a cross-correlation method. The action of nociceptive solutions of potassium chloride (125–1000 mM) on the saphenous nerve caused excitation of both myelinated and nonmyelinated fibers. The density of the spike train increased during the action of the stimulus up to a threshold sufficient for the appearance of nociceptive reflexes. The maximum of these reflexes coincided with the appearance of synchronous pulsations of discharges in the group of unmyelinated fibers. The nociceptive signal evoked by direct action of highly concentrated potassium chloride solutions on the nerve is thus coded by a high density of the spike train generated by the nerve fibers. Synchronous pulsations may be present in the spike train under these circumstances.
Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevski Gor'kii State University. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 598–605, November–December, 1977.