Transspinal Direct Current Stimulation Produces Persistent Plasticity in Human Motor Pathways

Abstract

The spinal cord is an integration center for descending, ascending, and segmental neural signals. Noninvasive transspinal stimulation may thus constitute an effective method for concomitant modulation of local and distal neural circuits. In this study, we established changes in cortical excitability and input/output function of corticospinal and spinal neural circuits before, at 0–15 and at 30–45 minutes after cathodal, anodal, and sham transspinal direct current stimulation (tsDCS) to the thoracic region in healthy individuals. We found that intracortical inhibition was different among stimulation polarities, however remained unchanged over time. Intracortical facilitation increased after cathodal and anodal tsDCS delivered with subjects seated, and decreased after cathodal tsDCS delivered with subjects lying supine. Both cathodal and anodal tsDCS increased corticospinal excitability, yet facilitation was larger and persisted for 30 minutes post stimulation only when cathodal tsDCS was delivered with subjects lying supine. Spinal input/output reflex function was decreased by cathodal and not anodal tsDCS. These changes may be attributed to altered spontaneous neural activity and membrane potentials of corticomotoneuronal cells by tsDCS involving similar mechanisms to those mediating motor learning. Our findings indicate that thoracic tsDCS has the ability to concomitantly alter cortical, corticospinal, and spinal motor output in humans.

Spinal direct current stimulation (tsDCS) in hereditary spastic paraplegias (HSP): A sham-controlled crossover study

“…To the best of our knowledge, this study is Although tsDCS mechanisms of action still remain debated, a growing body of evidence suggests that tsDCS interferes with cortical, corticospinal, and spinal motor output in humans. [36][37] Since spinal stimulation modulates both alpha and gamma motor neuron activity in animals, anodal tsDCS could directly inhibit gamma system in humans. 14,38 In addition, the pre-synaptic inhibition and post-activation depression induced by tsDCS could reduce spasticity by modulating interneuronal excitability.…”

Cortical and Subcortical Effects of Transcutaneous Spinal Cord Stimulation in Humans with Tetraplegia

“…During the sham-TESS session, the electrodes were located in the same position, and the intensity of stimulation was set as the same intensity as used in TESS sessions and gradually decreased down to 0 in ϳ1 min. Similar sham stimulation procedures have been used successfully in previous neuromodulation studies using TESS to provide the initial sensation of stimulation without the subsequent effects (Murray et al, 2018;Awosika et al, 2019). During TESS without 5 kHz carrier frequency (tested on subjects listed as 1-8 on Table 1), single biphasic pulses (200 s duration) were delivered at a 30 Hz frequency (every 33.1 ms) for 20 min using the same intensity as described above.…”

Transcutaneous spinal direct current stimulation increases corticospinal transmission and enhances voluntary motor output in humans

“…For clinical purposes, it would be desirable if the stimulation could be applied non-invasively and at intensities that are not painful. Lately, considerable interest has therefore been devoted to the possibility of modulating spinal neural transmission by transcutaneous application of a constant electrical direct current (DC) over the spinal cord; tsDCS (Berry, Tate, & Conway, 2017;Jankowska, 2017;Murray, Tahayori, & Knikou, 2018;Song & Martin, 2017). This has been spurred on by the demonstration that cortical DC stimulation may modulate cortical excitability and induce lasting plastic changes in cortical circuitry raising prospects of a clinical role in neurorehabilitation following brain lesion (Lefaucheur et al, 2017;Nitsche et al, 2008;Nitsche & Paulus, 2000).…”