Voluntary Modulation of Evoked Responses Generated by Epidural and Transcutaneous Spinal Stimulation in Humans with Spinal Cord Injury

Journal of Clinical Medicine, 2021 · DOI: 10.3390/jcm10214898 · Published: October 24, 2021

Simple Explanation

Transcutaneous (TSS) and epidural spinal stimulation (ESS) are techniques used to study how external electrical signals interact with spinal cord networks involved in movement. Pilot clinical trials have shown that ESS and TSS can restore motor functions lost due to spinal cord injury (SCI). This study examined how TSS or ESS pulses affect the lumbosacral spinal cord in nine individuals with chronic SCI, focusing on their ability to control leg flexion while lying down.

Study Duration

Not specified

Participants

9 individuals with chronic SCI

Evidence Level

Not specified

Key Findings

1
Lower-extremity muscles were activated similarly during TSS and ESS when participants were instructed to relax.
2
Both TSS- and ESS-evoked motor responses were significantly inhibited across all muscles when participants attempted lower-extremity muscle contractions.
3
Participants with clinically complete SCI tested with ESS and incomplete SCI tested with TSS showed a greater ability to modulate responses, although not statistically significant.

Research Summary

This study investigated the effects of voluntary control on TSS- and ESS-evoked responses in individuals with SCI. Participants were tested in relaxed conditions and while attempting maximal voluntary flexion of the lower extremities. The results indicated that during voluntary attempts to move paralyzed limbs, the evoked responses from both ESS and TSS were inhibited. The study also found that the ability to modulate evoked responses varied depending on the stimulation modality (ESS vs. TSS) and the severity of the spinal cord injury.

Practical Implications

Rehabilitation Strategies

These results suggest that descending commands combined with spinal stimulation may increase activity of inhibitory interneuronal circuitry within spinal sensorimotor networks in individuals with SCI, which may be relevant in the context of regaining functional motor outcomes.

Individualized Therapy

The option to choose a modality will likely result in the most desirable patient-speciﬁc outcome. Further studies are needed to demonstrate functional differences between TSS and ESS within the same individuals.

Understanding Spinal Mechanisms

These results suggest the interaction of supraspinal and spinal mechanisms even in individuals with severe SCI. Future work should focus on the role of effort at different stages from preparation to execution of the movement.

Study Limitations

1
SCI is a heterogeneous population and results may differ depending on location and severity of injury, time since injury, and age of participant
2
All of our experiments used low-frequency (0.2–2 Hz) stimulation in order to evaluate the effects of stimulation and voluntary effort without post-activation depression due to frequent stimulation.
3
All participants within this study were not trained to perform the task, and therefore may exhibit different results when part of a long-term study.

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