Author(s): THEODOSIADOU, A., SORDET, J., AMIRIDIS, I.G., MARTIN, A., PAPAIORDANIDOU, M., Institution: UNIVERSITÉ DE BOURGOGNE EUROPE, Country: FRANCE, Abstract-ID: 1686

INTRODUCTION:
Trans-spinal cord stimulation (tSCS) involves the transcutaneous application of electrical currents at the lumbar or thoracic spinal levels, inducing concomitant responses in lower-limb muscles. Evidence indicates that tSCS modulates spinal circuitry through the activation of sensory afferents(1). tSCS provides a valuable tool for investigating mechanisms underlying motor control(2,3) and counteracting the detrimental effects of immobilization in individuals with motor disorders(4). Despite its therapeutic potential, the optimal stimulation parameters remain poorly defined. Although current evidence suggests that variability in stimulation modalities does not alter the overall benefits, optimizing these parameters is essential to maximize outcomes(5). The aim of this study was to examine how different tSCS stimulation parameters influence the spinal excitability to propose relevant stimulation protocols for populations with motor deficits.
METHODS:
Twenty healthy young adults participated in a single experimental session consisting of ten 20-s trains of tSCS. Each train was delivered at 2 frequencies (30, 100Hz) and 5 intensities (60,80,90,100,120% of motor threshold [MT]). All procedures were performed with participants in a supine position. Peripheral nerve stimulation was used to record soleus H-reflex amplitude, while tSCS was also used to elicit trans-spinal evoked potentials (TEP). 1 Mmax, 4 H-reflexes, and 4 TEPs were recorded before and after each train. Mean values were calculated and normalized to soleus Mmax for analysis. Separate two-factor repeated-measures ANOVAs (Intensity×Time) were conducted for H-reflex and TEP amplitudes.
RESULTS:
No significant effects of Intensity nor Time were observed for H-reflex amplitude at the two frequencies, nor for TEP amplitude at 100Hz (p>0.05). In contrast, at 30Hz, a significant time effect (p=0.012) and Intensity×Time interaction (p=0.034) were found for soleus TEP amplitude. Specifically, TEP was reduced following the stimulation train at 120%MT compared with pre values (p=0.031).
CONCLUSION:
Our findings indicate that the acute effects of tSCS on spinal excitability could be frequency- and intensity-dependent. Specifically, a 30Hz 20s-train reduced soleus TEP amplitude at 120%MT, possibly due to increased pre-synaptic inhibitory mechanisms. This reduction of TEP and the preservation of H-reflex amplitude indicate that TEP seems more sensitive than the H-reflex to ionic changes occurring at the stimulation site. The preservation of spinal responses after the 100-Hz stimulation possibly indicates a concomitant modulation of excitatory and inhibitory mechanisms leading to no net effect.

References
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5. Rehman et al. (2023). J Clin Med;12(3):854.