Repeated transspinal stimulation decreases soleus H-reflex excitability and restores spinal inhibition in human spinal cord injury

PLoS ONE, 2019 · DOI: https://doi.org/10.1371/journal.pone.0223135 · Published: September 26, 2019

Spinal Cord Injury Neurology Neuroplasticity

Simple Explanation

This study investigates the effects of repeated transspinal stimulation on the soleus H-reflex, a measure of spinal cord excitability, in individuals with and without spinal cord injury (SCI). Transspinal stimulation involves applying electrical stimulation to the spinal cord through the skin. The researchers examined how repeated sessions of this stimulation affected the H-reflex and spinal inhibition, which is the ability of the spinal cord to suppress overactive reflexes. The results showed that repeated transspinal stimulation decreased the excitability of the soleus H-reflex in individuals with SCI, suggesting a restoration of spinal inhibitory control. This indicates that transspinal stimulation may be a useful non-invasive method for improving reflex actions after SCI.

Study Duration

Not specified

Participants

10 SCI and 10 healthy control subjects

Evidence Level

Not specified

Key Findings

1
Repeated transspinal stimulation reduced soleus H-reflex excitability in both motor incomplete and complete SCI, but not in healthy control subjects.
2
Transspinal stimulation restored the amplitude of monosynaptic motoneuron responses following repetitive excitation of muscle spindle group Ia afferents at low stimulation frequencies.
3
The study found that transspinal stimulation decreased the severity and frequency of spasms and ankle clonus in individuals with SCI.

Research Summary

This study investigated the impact of repeated cathodal transspinal stimulation on soleus H-reflex excitability and spinal inhibition in individuals with and without chronic SCI. The research involved administering monophasic transspinal stimuli and assessing changes in motoneuron recruitment, homosynaptic depression, and postactivation depression. The key findings revealed a decrease in soleus H-reflex excitability in both legs of SCI subjects, along with the presence of soleus H-reflex homosynaptic and postactivation depression. Repeated transspinal stimulation increased homosynaptic depression in all SCI subjects and reduced the severity of spasms and ankle clonus. The study concludes that repeated transspinal stimulation can decrease reflex hyperexcitability and restore spinal inhibitory control in the injured human spinal cord, suggesting its potential as a noninvasive neuromodulation method for restoring spinally-mediated afferent reflex actions after SCI in humans.

Practical Implications

Therapeutic Intervention

Transspinal stimulation can be used as a non-invasive method for restoring spinally-mediated afferent reflex actions after SCI in humans.

Complementation to Existing Therapies

Transspinal stimulation can complement conventional activity-based interventions in optimizing meaningful and long-lasting recovery from neurologic injury and disease.

Improvement of Motor Control

The decreased hyperreflexia, decreased spasticity and increased motoneuron output may benefit neural motor control and improve functional tasks such as standing and walking.

Study Limitations

1
Neurophysiological tests were not performed at different time points following cessation of stimulation.
2
The study only used a single, 1-ms square pulse at 0.2 Hz for transspinal stimulation.
3
The study cannot attribute the results exclusively to presynaptic mechanisms of neuroplasticity because the soleus H reflex at maximal amplitudes is not purely monosynaptic.

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