Comparison of somatosensory evoked potentials recorded from the scalp and dorsal column nuclei to upper and lower limb stimulation in the rat.

Responses from the dorsal column nuclei (DCN) in the rat to stimulation of the upper limbs (median nerve) and lower limbs (sciatic nerve) showed a difference in the wave forms of the two responses. These results support results of earlier studies in the cat, monkey, and man that showed that only slow-conducting cutaneous afferents from the lower limbs travel in the dorsal column, while all afferents from the upper limbs travel in the dorsal column and synapse in the DCN. A comparison between the response from the DCN and that from the vertex to stimulation of the upper limbs showed correspondence between short-latency peaks, while no clear earlier waves could be discerned in the response from the vertex to stimulation of the lower limbs. Even when the dorsal column was transected on one side, the correspondence between the early peaks in the scalp and the DCN responses to stimulation of the upper limbs was maintained. The effect of the dorsal column lesion on the response recorded from the surface of the DCN to stimulation of the sciatic nerve was mainly a reduction in the number of peaks. Transection at the midbrain level resulted in elimination of the long-latency response in the scalp recording, but the initial negative peak was maintained, which corresponded to the initial negative peak of the DCN response to stimulation of the upper limbs.