Epidural stimulation restores muscle synergies by modulating neural drives in participants with sensorimotor complete spinal cord injuries

Journal of NeuroEngineering and Rehabilitation, 2023 · DOI: https://doi.org/10.1186/s12984-023-01164-1 · Published: May 16, 2023

Spinal Cord Injury Neurology Neurorehabilitation

Simple Explanation

This study investigates how epidural spinal cord stimulation (eSCS) affects muscle coordination in individuals with motor-complete spinal cord injury (SCI). Researchers analyzed muscle activity complexity and muscle synergies with and without stimulation to understand its impact on neuromuscular control. The study found that eSCS immediately reduced the complexity of muscle activity in SCI participants. Over time, their muscle synergy structure became more defined, with fewer synergies needed, indicating improved coordination. The results suggest that eSCS helps restore muscle movements and synergies in SCI participants, but these movements are still different from those of healthy individuals.

Study Duration

Up to one year (13 follow-ups)

Participants

6 participants with chronic, motor and sensory complete SCI and 9 healthy participants

Evidence Level

Not specified

Key Findings

1
Epidural stimulation immediately reduces the complexity of muscle activity in SCI participants, bringing it closer to the complexity levels seen in healthy controls.
2
Long-term eSCS leads to a more defined muscle synergy structure in SCI participants, indicated by a decrease in the number of synergies required for movement.
3
Muscle synergies were restored with eSCS, supporting the neural hypothesis of muscle synergies, suggesting that these synergies originate from a neural source.

Research Summary

This study investigates the impact of epidural spinal cord stimulation (eSCS) on neuromuscular control in individuals with motor and sensory complete spinal cord injury (SCI). It analyzes changes in muscle activity complexity and muscle synergies with and without stimulation. The key findings reveal that eSCS reduces muscle activity complexity, leads to a more defined muscle synergy structure over time, and supports the neural origin of muscle synergies. These improvements suggest the restoration of muscle movements through neuromodulation. Despite the restoration of muscle synergies, the study highlights that the muscle synergies in SCI participants remain distinct from those in able-bodied controls, indicating persistent differences in neuromuscular control.

Practical Implications

Rehabilitation Strategies

eSCS can be integrated into rehabilitation programs for SCI patients to improve muscle coordination and volitional motor control.

Personalized Stimulation Parameters

Optimization of eSCS parameters can be tailored to individual needs to maximize the restoration of muscle synergies and motor function.

Understanding Neural Mechanisms

The findings support the neural basis of muscle synergies, guiding future research on targeted neuromodulation strategies.

Study Limitations

1
The study did not record hip extensor muscle groups, limiting the synergy analysis associated with hip extension.
2
EMG data normalization was performed using maximum muscle activation within each session due to the inability to record maximum voluntary contraction, which could affect the estimation of muscle loadings.
3
The supine posture of the participants made it difficult to record sEMG signals from the hamstrings and gluteus maximus.

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