Motor improvements enabled by spinal cord stimulation combined with physical training after spinal cord injury: review of experimental evidence in animals and humans

Bioelectronic Medicine, 2021 · DOI: https://doi.org/10.1186/s42234-021-00077-5 · Published: September 30, 2021

Spinal Cord Injury Neurology Neurorehabilitation

Simple Explanation

Electrical spinal cord stimulation (SCS) has emerged as a promising treatment for motor paralysis resulting from spinal cord injury (SCI). Combining SCS with activity-based training has led to significant improvements in motor function for individuals with chronic SCI, with effects persisting even without stimulation. SCS activates dormant spinal circuits below the injury by stimulating sensory afferents within the posterior roots. This understanding has led to standardized implant positions, consistently showing that SCS combined with physical training enhances motor performance and neurorecovery. Animal studies suggest that this neurorecovery involves synaptic reorganization of cortico-reticulo-spinal circuits, which improves voluntary motor control. Future research in both humans and animals is essential to fully understand the potential and limitations of SCS for various types and severities of SCI.

Study Duration

Not specified

Participants

8 participants with chronic SCI, varying in completeness (AIS A, B, C, D)

Evidence Level

Review of experimental evidence

Key Findings

1
SCS acts as a prosthetic, enabling individuals to move previously paralyzed limbs from the first day of implantation.
2
Individuals with SCI classified as AIS B and C regained motor function in paralyzed joints even without stimulation, but not individuals with motor and sensory complete SCI (AIS A).
3
Experiments in animal models of SCI investigating the potential mechanisms underpinning this neurorecovery suggest a synaptic reorganization of cortico-reticulo-spinal circuits that correlate with improvements in voluntary motor control.

Research Summary

This review examines the advancements in spinal cord stimulation (SCS) combined with activity-based training for motor paralysis after spinal cord injury (SCI). It highlights the use of SCS to activate dormant spinal circuits below the injury by recruiting sensory afferents. Clinical studies have demonstrated that SCS, when combined with physical training, leads to improvements in motor performance and neurorecovery. Notably, some individuals with incomplete SCI regained motor function even without stimulation. Animal studies suggest that SCS-mediated neurorecovery involves synaptic reorganization of cortico-reticulo-spinal circuits. Further research is necessary to understand the full potential and limitations of SCS for different types of SCI.

Practical Implications

Rehabilitation Strategies

SCS can be integrated into rehabilitation programs to amplify residual voluntary motor control and promote lasting improvements in motor function.

Patient Selection

Assessment of residual supra-spinal inputs could improve patient selection and optimize rehabilitation protocols for individuals with different severities of SCI.

Training Activities

Training programs should maximize volitional inputs while implementing diverse types of tasks to promote circuit-specific plasticity via SCS.

Study Limitations

1
Small population sizes in clinical trials limit definitive conclusions about recovery outcomes.
2
Mechanisms of SCS-mediated recovery after severe contusions remain largely debated and unexplored.
3
Need for further research on factors affecting responsiveness to SCS, such as sex, race, genetics, and economic backgrounds

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