University of Twente Student Theses


Trans-Spinal Direct Current Stimulation in Incomplete Spinal Cord Injury Subjects: Analysis of Motor Unit Activity for a New Class of Biomarkers

Gogeascoechea Hernandez, A.D.J. (2019) Trans-Spinal Direct Current Stimulation in Incomplete Spinal Cord Injury Subjects: Analysis of Motor Unit Activity for a New Class of Biomarkers.

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Abstract:Electrophysiological changes after trans-spinal direct current stimulation (tsDCS) in incomplete spinal cord injury (SCI) subjects are not well understood. Presumably, cathodal tsDCS facilitates motor function after stimulation is administered in healthy subjects. The aim of this study is to investigate motor unit (MU) features that help describe the effects of tsDCS on incomplete SCI subjects. Based on the data of the double-blind, sham-controlled crossover study of Kuck et al., neural activity of the soleus muscle from one chronic, incomplete SCI subject was analyzed in time and frequency domain. The protocol recorded high density-electromyography (HD-EMG) during plantar flexion sub-maximal contractions before and just after cathodal and sham tsDCS (2.5 mA, 15 min). In frequency domain, several features were obtained from the coherence between two cumulative spike trains (CSTs), which were generated from sets of single motor units (MUs). The coherence peaks and areas of the delta band (0-5 Hz) showed a decrease after cathodal tsDCS and no effect after sham tsDCS. This suggests that cathodal tsDCS decreases the strength of the common drive, which is likely due to an enhanced afferent feedback as secondary common synaptic input. Supporting this hypothesis, it was also found that the number of MUs in the CSTs reaching a plateau in coherence was greater after cathodal tsDCS. In time domain, a decrease in the cross-correlation peaks between smoothed CSTs confirmed the decrease in strength of the common drive found in frequency domain. Moreover, the coefficient of variation of the smoothed CSTs indicated a possible increase in steadiness (decrease in fluctuations) after cathodal tsDCS and no change after sham tsDCS. However, the coefficient of variation of the first common component (FCC, first principal component) as well as the average discharge rate did not reveal any change. The present study provides a novel MU-based analysis of the effects of cathodal tsDCS on lower limb motor impairment due to incomplete SCI. At a later stage, these findings may lead to robust biomarkers for a closed-loop modulation of the corticospinal excitability.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:50 technical science in general, 53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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