Long-latency spinal reflex in man after flexor reflex afferent stimulation

Area of Science:

• Neuroscience
• Spinal Cord Injury Research
• Electrophysiology

Background:

• Clinically complete spinal cord transection impairs voluntary motor control.
• Understanding residual reflex pathways is crucial for rehabilitation strategies.

Purpose of the Study:

• To investigate electromyographic (EMG) flexor muscle responses to peripheral nerve stimulation in spinal cord transection patients.
• To characterize the properties of early and late reflex responses.

Main Methods:

• Electromyographic recordings from tibialis anterior, biceps femoris, and rectus femoris.
• Electrical stimulation of sural (cutaneous) and tibial (mixed) nerves in 16 patients.
• Analysis of reflex response latencies and thresholds.

Main Results:

• Distinct early (approx. 75-100 ms latency) and late (approx. 130 ms latency) ipsilateral flexor muscle responses were elicited.
• The late response exhibited a striking latency increase with stimulus intensity (up to 450 ms).
• Late reflex characteristics were similar to those observed in animal models of spinalization.

Conclusions:

• Both early and late flexor responses are directly elicited by afferent volleys, not peripheral loops.
• The late reflex involves spinal pathways with significant central delay (>100 ms).
• Findings provide insights into spinal reflex mechanisms post-transection.