Cortifugal influences on dorsal column nuclei: an electrophysiological study in the rat using the cortical spreading depression technique.

The sign and duration of corticofugal effects on the extracellularly recorded spontaneous activity of cuneate and gracile neurons were examined by means of the cortical spreading depression technique (CSD). Among the 40 units studied 22 showed changes in their spontaneous firing rate during the passage of a CSD. Changes were of either short (5-20 s) or long (greater than 20-140 s) duration. Increases and decreases in activity, as well as sequences of both types of alteration were observed. Short duration changes were more frequent and much more pronounced than those of long duration. From their time course and intensity the short duration effects seem to be related to the brief high frequency cortical neuron discharge that precedes the cortical silence due to CSD, whereas the long lasting effects seem related to the cortical block. It is concluded that the most important corticofugal effects on gracile and cuneate neurons are phasic in nature and the sensorimotor cortical regions were found to be responsible for these influences.