Patterned response of lamina V cells: cutaneous and dorsal funicular stimulation

Single unit activity was recorded in spinal lamina V (LV) in unansthetized cats. Poststimulus-time histogram (PSTH) analysis of responses to intracutaneous stimulation demonstrated similar firing patterns for all cells. In addition to a direct relationship between stimulus intensity and the duration of cellular response, modulation of firing frequency and distinct delayed PSTH peaks in 77 percent of the units were observed. The pattern of delayed peaks was associated with the same high intensity intracutaneous stimulation reported as painful when applied to human observers. A background of dorsal funicular stimulation selectively inhibited the delayed response of LV cells to high intensity stimulation. Thus, LV cells, by their duration of firing, trasmit information related to stimulus intensity, and by their patterned responses, have the potential to relay other information, possibly related to their nociceptive role. As delayed LV activity is associated with a high proportion of small fibers in the afferent input, presynaptic inhibition of A-delta and C fibers might account for the selective inhibition associated with dorsal funicular stimulation.