O203 Neuromodulation of lower limb motor circuitry with transcutaneous lumbar spinal cord direct current stimulation

Abstract

Objectives The advent of transcranial direct current stimulation (tDCS) introduced growing interest in modulating spinal circuits, altered in many neurologic conditions. Transcutaneous spinal direct current stimulation (tsDCS) of cervical and thoracic spine regions was observed to modulate sensory and motor responses. Combining clinical studies with computational modelling can be a powerful tool to establish tsDCS protocols for specific therapeutic purposes. The aim of this study was to measure the effects of tsDCS delivered on the lumbar region on motor spinal responses and observe if these were consistent with the electric field (E-field) distribution predicted in the spinal cord using a computational model. Methods The exploratory study design was double-blind crossover pseudo-randomized. tsDCS was delivered for 15 min (anodal, cathodal, sham) at L2 vertebra level (2.5 mA, 90 C/cm2) in 15 healthy subjects. The F-wave, H-reflex, cortical silent period, motor evoked potential and sympathetic skin response were analysed. Statistical methods were applied with Bonferroni correction for multiple comparisons (p = 0.05). A human volume conductor model was obtained from available databases. E-field distributions in the spinal grey matter (GM) and white matter (WM) were calculated considering the same protocol and tissue conductivities based on literature review. Results We observed the increase of the F-wave mean latency, however this was independent of the type of intervention. No other differences were observed (p > 0.05, Bonferroni corrected). The E-field magnitude predicted for the lumbosacral spinal GM and WM was 0.15 V/m in protocols with observed modulation of motor responses. Discussion Therefore, the E-field obtained is not sufficient to ensure neuromodulation, which is consistent with the absence of effects observed. The tsDCS protocol applied did not change motor response to delivered stimulus, having no effect on lumbosacral motor circuits. Conclusions Future studies should address diversified protocols sustained in computational models. Significance Computer models of E-field for tsDCS should be optimized to increase chances of a biological effect.