Spinal cord potentials evoked by peripheral nerve stimulation.

Lumbar, thoracic, and cervical spinal cord responses evoked by sciatic nerve stimulation were measured in 20 cats at the skin level and directly from the dorsal surface of the cord. Computer averaging techniques were used for both skin level recordings and cord surface recordings at all levels. Recordings made directly from the cord surface at lumbar levels were large and were characterized by a large, initial, negative transient, followed by a more complicated and variable waveform. As recording electrodes were moved rostrally, the initial large spike decreased in amplitude and the duration and latency of the response increased. At cervical levels were large and were characterized by a large, initial, negative transient, followed by a more complicated and variable waveform. As recording electrodes were moved rostrally, the initial large spike decreased in amplitude and the duration and latency of the response increased. At cervical levels the responses were polyphasic, of long duration and small amplitude. Deafferentation by posterior rhizotomy of all lumbar and sacral roots ipsilateral to sciatic nerve stimulation abolished the response at all levels. Thoracic cord section also abolished the response over the cervical cord. Skin level recordings were of shorter latency than direct recordings, especially at cervical levels. Response configurations were similar for both recording techniques at lumbar levels, but had different waveforms at both thoracic and cervical levels. Clinical implications of the techniques and possible explanations of the waveforms recorded are discussed.