Relation between the specific H reflex facilitation preceding a voluntary movement and movement parameters in man.

Abstract

SUMMARY1. In a reaction-time situation, the monosynaptic spinal reflex (H reflex) is facilitated before the onset of an electromyographic (e.m.g.) response. The aim of the present investigation was to study aspects of this facilitation.-2. Human subjects were required to perform isometric plantarflexions of the foot in response to a visual stimulus. The movement was always on the same side in the simple reaction-time situation, and randomly with the right or left foot in the choice reaction-time situation. Stimuli to evoke H reflexes were applied bilaterally 40-400 ms after the onset of the visual stimulus. Pre-motor time, i.e. the interval between the onset of the visual stimulus and the e.m.g. response, and reaction time, i.e. the interval between the onset of the visual stimulus and the response on the torque recording, were computed.3. In both reaction-time situations, there was a significant facilitation of the ipsilateral H reflex 100-160 ms before e.m.g. onset and, in some subjects, a small facilitation of the contralateral H reflex. The specific facilitation, i.e. the difference between the facilitation on the ipsi-and contralateral side relative to the movement, was not significantly different on the right and left side.4. Pre-motor time was divided into the interval from the light onset until the onset of the specific facilitation, and the interval from the onset of the facilitation until the onset of the voluntary response. Both intervals increased, and the slope and the amplitude of the facilitation decreased with increasing pre-motor time and reaction time.5. The specificity of the H reflex facilitation in a choice reaction-time situation implies that the interval from light onset until the onset of the facilitation includes stimulus identification and response selection, and the interval from the onset of the facilitation until the e.m.g. response preparation of the motor system for the required movement.6. The present results suggest that the specific facilitation of the H reflex before a movement is caused by removal of presynaptic inhibition at I a terminals or by activation of interneurones intercalated in polysynaptic components of the H reflex rather than by a subthreshold activation of motoneurones. PHY 34718

Spinal Reflexes In Microgravity: Measuring H Reflexes During Space Flight

“…Facilitatory effects of about 40 percent are well within the range we have obtained in a reaction time task (4 (2).…”

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

“…This gradual rise in the corticospinal excitability is concomitantly evidenced by parallel enhancements in MEPs of the target muscle (Pascual-Leone et al 1992;Chen and Hallett 1999). Secondly, enhanced excitability during this period occurs along the neuroaxis, including the spinal level (Eichenberger and Ruegg 1984). Thirdly, motor imagery enhances the corticospinal excitability, including the spinal levels .…”

Time course of motor excitability before and after a task-related movement

“…Spinal contribution to excitability changes may be due to corticofugal influences before movement or to afferent inputs following the movement. Spinal facilitation has been demonstrated only between 50 and 100 ms before EMG onset [6,11] and thus cannot explain the excitability changes beyond this time period. The effect of afferent inputs after movement is unlikely because afferent inputs have been shown not to affect spinal motoneuron or interneuron excitability [20].…”