SPINAL TRACTS PRODUCING SLOW COMPONENTS OF SPINAL-CORD POTENTIALS-EVOKED BY DESCENDING VOLLEYS IN MAN

Slow negative (N) and slow positive (P) waves are frequently produced in the posterior epidural space at the lumbosacral enlargement by epid ural stimulation of the rostral part of human spinal cord. The product ion of these slow potentials are thought to be responsible for analges ia at the stimulated segment as well as below that level. In order to define the spinal tract which mediates these slow potentials, we stimu lated directly or from the epidural space the dorsal, dorsolateral, la teral and ventral columns at the cervical or thoracic level, and epidu rally recorded spinal cord potentials (des.SCPs) at the lumbosacral en largement in 7 patients who underwent spine or spinal cord surgery. Th e des.SCPs recorded in the lumbosacral enlargement consisted of polyph asic spike potentials followed by slow N and P waves. At a near thresh old level of stimulus intensity the slow N and P potentials were consi stently elicited only by stimulation of the dorsal column. The slow wa ves were also produced by intense stimulation of other tracts, bur rem ained significantly (P < 0.05-P < 0.01) smaller than those evoked by d orsal column stimulation when compared at the same stimulus intensity. Moreover, the slow P wave could not be elicited even by intense stimu lation (10 times the threshold strength for the initial spike potentia ls) of the ventral column. Thus, the results suggest that the slow N a nd P waves are mostly mediated by the antidromic impulses descending t hrough the dorsal column.