The Immediate and Short-Term Effects of Transcutaneous Spinal Cord Stimulation and Peripheral Nerve Stimulation on Corticospinal Excitability

Frontiers in Neuroscience, 2021 · DOI: 10.3389/fnins.2021.749042 · Published: October 21, 2021

Spinal Cord Injury Neurology Rehabilitation

Simple Explanation

This study explores how electrical stimulation can help people with spinal cord injuries recover motor function. It looks at the immediate and short-term effects of different types of electrical stimulation on the spinal cord and nerves. The researchers used transcranial magnetic stimulation (TMS) along with transcutaneous spinal cord stimulation (tSCS) and peripheral nerve stimulation (PNS) to see how these techniques affect the excitability of the pathways between the brain and the muscles. The study found that pairing TMS with tSCS can increase the excitability of these pathways and improve motor performance. They also compared different types of tSCS to see which was most effective.

Study Duration

Not specified

Participants

Healthy subjects; Experiment I: 24, Experiment II: 20, Experiment III: 10

Evidence Level

Original Research

Key Findings

1
Repeated pairing of TMS and tSCS, timed to coincide at the alpha-motoneurone, increases corticospinal excitability and influences functional motor output.
2
Short trains of tSCS applied at motor threshold immediately facilitate subsequent motor-evoked potentials at inter-stimulus intervals of 30-50 ms.
3
Motor thresholds were substantially higher when delivering tSCS in a single HF (10kHz) burst compared with a single pulse of tSCS (square wave).

Research Summary

The study investigated the effects of tSCS and PNS on corticospinal excitability in healthy subjects using TMS. Three experiments were conducted to compare different stimulation parameters and their impact on motor performance. Experiment I showed that repeated pairing of TMS and tSCS, timed to arrive simultaneously at the alpha-motoneurone, increased corticospinal excitability and influenced motor performance. Experiments II and III compared the immediate effects of tSCS and PNS, as well as different tSCS waveforms, on corticospinal excitability, revealing that short trains of tSCS facilitated motor-evoked potentials, while HF-tSCS required higher currents and had a lesser effect.

Practical Implications

Optimizing Stimulation Parameters

The findings suggest that careful timing and pairing of TMS and tSCS can enhance corticospinal excitability, which could be beneficial for neuroplasticity in SCI patients.

Immediate Enhancement of Excitability

Short trains of tSCS can quickly improve corticospinal excitability, potentially leading to immediate improvements in motor control for individuals with SCI.

Waveform Considerations

The study highlights the importance of waveform selection (traditional vs. HF) for tSCS, as HF waveforms require higher currents and may have different underlying mechanisms.

Study Limitations

1
The mechanisms observed in healthy participants may not fully translate to people with SCI.
2
Only two ISIs were tested in Experiment I, so the effects may not be entirely due to STDP.
3
The comparison between tSCS and HF tSCS in experiment III was done at only one ISI.

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