Spinal facilitation of descending motor input

bioRxiv preprint, 2023 · DOI: https://doi.org/10.1101/2023.06.30.547229 · Published: July 3, 2023

Simple Explanation

The study investigates how Dynamic Stimulation (DS), a type of spinal electrical stimulation, affects motor responses, especially after spinal injury. It uses a corticospinal platform to selectively stimulate the cortex while measuring electrical activity in the spinal cord. The researchers validated their epidural interface by measuring cord dorsum potentials (CDPs) in response to peripheral nerve stimulation. They found that DS increases the excitability of spinal interneurons that process corticospinal input. The findings support the use of electrical neuromodulation to improve motor output when volitional input is weak, such as due to partial disconnection from supraspinal structures or brain dysfunctions.

Study Duration

Not specified

Participants

24 adult male and female Wistar rats (250 - 300 g body weight)

Evidence Level

Not specified

Key Findings

1
Dynamic Stimulation (DS) selectively increases the excitability of spinal interneurons that first process corticospinal input, without altering the magnitude of commands from the motor cortex.
2
DS increases the excitability of post-synaptic spinal interneurons at the stimulation site, enhancing their responsiveness to residual supraspinal control.
3
The study established a novel correlation between muscle recruitment and components of cortically-evoked CDPs, suggesting a link between spinal interneuron activity and motor output.

Research Summary

The study investigates the effects of Dynamic Stimulation (DS) on corticospinal motor responses using a corticospinal platform in rats. The platform allows for selective cortical stimulation and simultaneous acquisition of cord dorsum potentials (CDPs). The results show that DS selectively increases the excitability of spinal interneurons involved in processing corticospinal input, without changing the magnitude of descending commands from the motor cortex. This suggests a postsynaptic facilitation of spinal networks. The study supports the use of electrical neuromodulation in cases where motor output is compromised due to weak volitional input, such as in spinal cord injury or brain dysfunctions, by enhancing the responsiveness of spinal interneurons to residual supraspinal control.

Practical Implications

Neurorehabilitation Strategies

The findings suggest that neuromodulation strategies, particularly Dynamic Stimulation (DS), can be targeted at spinal interneurons to enhance motor recovery after SCI or in cases of neuronal brain dysfunctions.

Technological Advancement

The study validates the use of multi-electrode arrays for simultaneous stimulation and recording of spinal cord activity, paving the way for more advanced clinical interfaces that can provide real-time feedback on stimulation efficiency.

Understanding Spinal Circuits

The research provides insights into the mechanisms of spinal neuromodulation, particularly its effects on spinal interneuron excitability and responsiveness to descending motor commands, which can inform the development of more effective therapeutic interventions.

Study Limitations

1
The study was conducted on anesthetized rats, which may limit the generalizability of the findings to awake, behaving animals.
2
The exact identity of the spinal interneurons responsible for the P2 wave was not determined.
3
The study did not fully titrate the amplitude of presynaptic input in response to cortical stimulation, potentially limiting the understanding of presynaptic effects.

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