Facilitation During the H-Reflex Recovery Cycle

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Abstract
A period of facilitation at 200 msec has been studied in the H-reflex recovery cycle, or period during which a second (test) reflex is influenced by a first (conditioning). Three main experiments were performed on normal and quadriplegic patients: (1) identical conditioning and test stimuli to same leg; (2) liminal conditioning and maximum test stimuli to same leg; and (3) maximum conditioning contralateral leg, maximum test ipsilateral leg. Both normal and quadriplegic subjects had facilitation in each experiment at about 200 msec. Our data are interpreted as not supporting a long loop reflex producing this facillitation. We suggest this facilitation is the interaction of afferent activity in large diameter axons with the physiological tremor, whose first subharmonic is 200 msec.