ERBS POINT STIMULATION PRODUCES SLOW POSITIVE POTENTIALS IN THE HUMANLUMBAR SPINAL-CORD

Evoked spinal cord potentials (SCPs) were recorded from the posterior epidural space (PES) at the cervical and lumbrosacral enlargements in response to electrical stimulation of the brachial plexus at Erb's poi nt in 17 chronic pain patients. Erb's point stimulation produced slow positive potentials (heterosegmental slow positive potentials, HSPs) i n the PES at the lumbrosacral enlargement in all 13 subjects without s pinal cord lesions but not in 4 subjects with spinal cord lesions. The HSP1 with a central peak latency of 21 +/- 2 ms (mean +/- SE) was rec orded at the stimulus intensity up to two to three times the threshold strength (T) of the initially positive spike (P1) of the segmental SC P, which was simultaneously recorded from the PES at the cervical enla rgement At the stimulus intensity of more than 3T, another slow positi ve potential (HSP2) with central peak latency of 71 +/- 6 ms was recor ded. These slow positive potentials (HSP1 and HSP2) might be produced by a feedback loop via supraspinal structures, presumably primary affe rent depolarizations, in comparison to the HSPs of our previous studie s in the rat. Slow negative potentials were sometimes noted before (5 of 13) and/or after (2 of 13) the HSP1. These slow negative potentials probably reflect the activities of dorsal horn neurons producing the HSP1 and HSP2, respectively, also elicited by a feedback loop via supr aspinal structures.