Transspinal stimulation downregulates flexion reflex pathways during walking in healthy humans

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation Science

Background:

• The tibialis anterior (TA) flexion reflex is crucial for locomotion.
• Understanding how spinal stimulation affects reflexes is key for neurological rehabilitation.
• Transspinal stimulation (TSS) is a potential tool for modulating spinal circuits.

Purpose of the Study:

• To investigate the phase-dependent modulation of the TA flexion reflex during treadmill walking.
• To determine the effects of transspinal stimulation (TSS) at various frequencies and intensities on this reflex.
• To explore the potential of TSS for modulating spinal neuronal networks involved in walking.

Main Methods:

• Participants underwent transspinal stimulation (TSS) at 15, 30, and 50 Hz, above and below paresthesia.
• The tibialis anterior (TA) flexion reflex was elicited by medial arch foot stimulation during treadmill walking.
• Reflex activity was measured across the step cycle and normalized to maximal TA activity.

Main Results:

• The unconditioned flexion reflex showed phase-dependent modulation during walking.
• TSS consistently produced a pronounced depression of the TA flexion reflex across all tested frequencies and intensities.
• This depression occurred without altering the relationship between reflex activity and background EMG, suggesting specific pathway modulation.

Conclusions:

• Transspinal stimulation (TSS) effectively downregulates the tibialis anterior (TA) flexion reflex during walking in healthy individuals.
• Findings suggest TSS primarily affects flexion reflex pathways, not extension pathways (like the soleus H-reflex).
• This neuromodulation of spinal networks offers potential therapeutic benefits for improving walking after spinal cord injury by suppressing exaggerated reflexes.