M. Tomita et al., SPINAL TRACTS PRODUCING SLOW COMPONENTS OF SPINAL-CORD POTENTIALS-EVOKED BY DESCENDING VOLLEYS IN MAN, Electroencephalography and clinical neurophysiology. Evoked potentials, 100(1), 1996, pp. 68-73
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.