The effects of interaction between large and small diameter fiber systems on the somatosensory evoked potential

The effect of interaction between large and small diameter fiber systems on the somatosensory evoked potential (SEP) was studied in anesthetized cats. Activation of large diameter fibers of the peroneal or radial nerves eliminates the late components of the SEP produced by stimulation of all fibers in the contralateral median or radial nerves. The inhibitory effects of a selective conditioning stimulus to the large diameter fibers of the peroneal nerve on the radial nerve evoked SEP was eliminated by bilateral transection of the dorsal column and spino-cervical tracts. However, interaction could still be obtained following transection when both large and small diameter fibers in the peroneal nerve were stimulated. The results of this study support the hypothesis that a correlation exists between activity in different fiber groups in afferent nerves, their conduction pathways through the cord, and the components of the cortical evoked potential.