Spinal evoked potential in the monkey

Abstract

Computer-averaged evoked potential responses (EPs) to stimulation of the sciatic nerve and cervical spinal cord were recorded from the dura and skin over the causda equina and spinal cord in seven monkeys, three with chronic spinal cord lesions. Sciatic EPs consited of predominantly negative triphasic propagated potentials recorded at all spinal levels and greatest in amplitude over the cauda equina and caudal spinal cord. The conduction velocity of this EP was faster over the cauda equina and rostral spinal cord than over caudal cord segments. Triphasic potentials were succeeded by small negative potentials over the cauda equina and larger negative potentials over the lumbar enlargement. Sciatic EPs over the upper lumbar and thoracic cord were more sensitive to asphyxia than the initial triphasic potentials recorded over cauda equina and caudal cord but resisted changes from increasing the rate of stimulation up to 100 per second. Propagated thoracic EPs were preceded by nonpropagated potentials. The longer latency negative potentials occurring locally over the cauda equina and lower lumbar enlargement were abolished at levels of asphyxia and were attenuated at rates of stimulation that did not affect the preceding triphasic potentials. Following complete spinal cord transection, nonpropagated sciatic EPs were recorded in leads rostral to the section. In preparations with chronic partial cord hemisection involving dorsal and lateral quadrants, ipsilateral sciatic EPs had increased latency, reduced amplitude, and poor definition in the vicinity of and rostral to the lesion. Direct cervical cord stimulation elicited caudally propagated potentials which were followed by large, broad potentials over the number enlargement.

Waveform changes due to conduction block and their underlying mechanism in spinal somatosensory evoked potential: a computer simulation

“…The computer model described above predicted that localization of the precise site of the conduction block can be achieved by demonstrating an abrupt reduction in the amplitude of the spinal SSEP, which is accompanied by an increased negative wave caudally and a monophasic pos-itive wave rostrally. In animal studies, the augmentation of the unipolarly recorded spinal SSEP has been observed in the lead immediately caudal to the site of the lesion caused by acute sectioning 9 or subacute compression 24 of the spinal cord. In human studies using unipolar leads, the phenomenon has received little attention, although it is evident in figures 27,36 showing spinal SSEP recordings for cervical spondylotic myelopathy.…”

Paradoxical enhancement of spinal-cord-evoked potentials rostral and caudal to the site of progressive cord compression in the cat

“…In previous animal studies, the enhancement of SCEPs was observed immediately caudal to the site of acute cord sectioning 15 or subacute cord compression.…”

Spinal somatosensory evoked potentials in juvenile diabetes

“…The broader, more complex potential recorded over caudal cord segments reflects activity in intramedullary continuations of dorsal root fibers and synaptic activity in neurons concerned with local reflex mechanisms 141. Potentials recorded over rostral cord segments arise in multiple rapidly conducting afferent tracts that lie primarily ipsilateral to the stimulated nerve [9,201 reflects branching of dorsal root fibers and synaptic activity in this region, where fibers undergo synaptic contact in Clarke's column and other nuclei. All these conduction velocities are lower in the infant and progressively increase with age.…”

“…Spinal somatosensory evoked potentials to lower limb stimulation recorded from surface electrodes have been studied in both humans and animals [3,4,9,15,18,201. In reference recordings over the cauda equina, an initial triphasic potential is often followed by a second, negative potential or inflection.…”