Abstract
It is the thesis of this review that the origin of the intercurrent facilitation at 50 to 400 msec in the standard recovery curve of the H reflex, evoked with paired stimuli, is a complex. It is composed importantly of central feedback effects from the conditioning reflex contraction, influences mediated by cutaneous group III afferent nerve fibres excited by the percutaneous stimulus, and with a possible additional modest contribution by long-loop, spino-bulbo-spinal influences.