Facilitation of the dorsal root potentials by volleys spreading caudally and cranially in the spinal cord.

Conditioning volleys spreading along 3 segments of the cord produce larger facilitation of bilateral dorsal root potentials in sacral cord than volleys in neighbouring dorsal roots used to evoke the testing depolarization. Contralateral potentials are more facilitated by volleys descending from lumbar than ascending from caudal segments.