Lumbosacral spinal evoked potentials in humans.

Evoked potentials in response to submaximal electrical stimuli to the peroneal or tibial nerves were recorded from the lumbosacral region in 18 normal subjects. Averaging of 128 responses from recording electrodes over spinous processes S1 to T11, with a reference electrode on the contralateral iliac crest, demonstrated potentials of 0.5 to 1.8 microV, with two well-defined negative peaks having latencies proportional to the distance between the stimulating and recording electrodes. The first peak originated from a traveling wave of depolarization in afferent fibers in the cauda equina, and the second peak originated in the spinal cord. F waves, H reflexes, microreflexes, and volume-conducted muscle responses did not contribute to these potentials.