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

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• The monosynaptic spinal reflex (H reflex) is known to be facilitated before voluntary electromyographic (e.m.g.) responses.
• Understanding the precise timing and nature of this facilitation is crucial for comprehending motor preparation.

Purpose of the Study:

• To investigate the temporal characteristics and specificity of H reflex facilitation preceding voluntary plantarflexion.
• To differentiate between ipsilateral and contralateral H reflex modulation during reaction-time tasks.

Main Methods:

• Human subjects performed isometric plantarflexions in simple and choice reaction-time tasks.
• H reflexes were evoked bilaterally via electrical stimulation at various intervals after visual stimuli.
• Pre-motor time and reaction time were measured, alongside H reflex amplitude changes.

Main Results:

• Significant ipsilateral H reflex facilitation occurred 100-160 ms before e.m.g. onset in both reaction-time conditions.
• A smaller contralateral facilitation was observed in some subjects.
• Both early and late phases of pre-motor time increased with longer reaction times, with decreased facilitation slope and amplitude.

Conclusions:

• The specific facilitation of the H reflex suggests a removal of presynaptic inhibition at Ia terminals or activation of interneurons.
• The timing of H reflex facilitation differentiates between stimulus processing/response selection and motor system preparation.
• These findings offer insights into the neural mechanisms underlying voluntary movement initiation.