Mapping the Iceberg of Autonomic Recovery: Mechanistic Underpinnings of Neuromodulation following Spinal Cord Injury

The Neuroscientist, 2024 · DOI: 10.1177/10738584221145570 · Published: January 1, 2023

Simple Explanation

Spinal cord injury (SCI) disrupts communication between the spinal cord and brain, leading to sensorimotor and autonomic impairments. Restoring autonomic function is a high priority for individuals with SCI due to its impact on quality of life. Spinal cord stimulation (SCS) is emerging as a promising approach for restoring autonomic function after SCI. SCS involves applying electrical current to the spinal cord to promote functional recovery. This review explores the mechanisms by which SCS may restore autonomic functions like cardiovascular, bowel, and lower urinary tract (LUT) function, focusing on somatoautonomic reflexes and neuroplasticity.

Study Duration

Not specified

Participants

Preclinical and clinical evidence

Evidence Level

Review

Key Findings

1
SCS likely activates the somatoautonomic reflex arc by stimulating primary afferent fibers, spinal interneurons, and autonomic efferent pathways, resulting in targeted responses in visceral organs.
2
SCS may promote neuroplasticity in spinal autonomic circuits by preserving myelin, promoting remyelination, and encouraging axon sprouting and regeneration.
3
SCS shows potential in mitigating orthostatic hypotension by activating sympathetic spinal cord circuits and mitigating autonomic dysreflexia by inhibiting visceral/noxious sensory transmission.

Research Summary

This review explores the mechanisms underlying the effects of spinal cord stimulation (SCS) for autonomic recovery following spinal cord injury (SCI). Two plausible mechanisms are discussed: activation of somatoautonomic reflexes and facilitation of neuroplasticity of spinal autonomic pathways. The review highlights areas where evidence is limited, guiding future research to further explore these mechanisms and advance the clinical translation of SCS for autonomic recovery.

Practical Implications

Targeted neuromodulation strategies

Understanding the specific spinal circuits activated by SCS for different autonomic functions can lead to more targeted and effective neuromodulation strategies.

Personalized SCS protocols

Identifying the optimal SCS parameters (e.g., stimulation site, frequency, intensity) for individual patients based on their specific autonomic deficits could improve outcomes.

Combination therapies

Combining SCS with other rehabilitation strategies, such as exercise and pharmacological interventions, may enhance neuroplasticity and functional recovery.

Study Limitations

1
Lack of direct evidence for the activation of sympathetic preganglionic neurons (SPNs) by SCS in mitigating orthostatic hypotension.
2
Limited mechanistic evidence on the activation of inhibitory interneurons or the decrease of sensory transmission by SCS in inhibiting autonomic dysreflexia.
3
The effect of SCS on LUT function is still not fully understood, with some case reports suggesting adverse effects such as urinary incontinence.

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