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Randomized Controlled Trial
. 2019 Oct 25;16(1):123.
doi: 10.1186/s12984-019-0589-6.

Cervical trans-spinal direct current stimulation: a modelling-experimental approach

Sofia Rita Fernandes  1   2 , Mariana Pereira  3 , Ricardo Salvador  4 , Pedro Cavaleiro Miranda  5 , Mamede de Carvalho  3   6
Affiliations
Randomized Controlled Trial

Cervical trans-spinal direct current stimulation: a modelling-experimental approach

Sofia Rita Fernandes et al. J Neuroeng Rehabil. .

Abstract

Background: Trans-spinal direct current stimulation (tsDCS) is a non-invasive technique with promising neuromodulatory effects on spinal cord (SC) circuitry. Computational studies are essential to guide effective tsDCS protocols for specific clinical applications. This study aims to combine modelling and experimental studies to determine the electrode montage that maximizes electric field (E-field) delivery during cervical tsDCS.

Methods: Current and E-field distributions in the cervical SC were predicted for four electrode montages in a human realistic model using computational methods. A double-blind crossover and randomized exploratory study was conducted using the montage that maximized E-field delivery. tsDCS was applied for 15 min in 10 healthy subjects (anodal, cathodal, sham, with polarity assigned to the cervical electrode), with a current intensity of 2.5 mA, resulting in a total current charge density delivery of 90 mC/cm2. Upper limb motor (transcranial magnetic stimulation) and sensory evoked potentials (MEP, SEP), M-waves, H-reflex and F-wave responses were analysed. Central and peripheral conduction times were determined using MEP. Repeated measures ANOVA and Friedman test were used for statistical analysis (significance level α = 0.05).

Results: All montages presented higher current density and E-field magnitudes in the cervical SC region between the electrodes. However, electrodes at C3 and T3 spinous processes (C3-T3) originated the highest E-field magnitude (0.50 V/m). Using C3-T3 montage we observed significant changes in N9 SEP latency (p = 0.006), but significance did not persist in pairwise comparisons (sham-anodal: p = 0.022; sham-cathodal: p = 0.619; anodal-cathodal: p = 0.018; α = 0.017, Bonferroni corrected). MEP latency and central motor conduction time (CMCT) modified significantly on stimulation (p = 0.007 and p = 0.015, respectively). In addition, pairwise comparisons confirmed significant differences between sham and cathodal conditions after Bonferroni correction for MEP latency (sham-anodal: p = 0.868; sham-cathodal: p = 0.011; anodal-cathodal: p = 0.023) and CMCT (sham-anodal: p = 0.929; sham-cathodal: p = 0.010; anodal-cathodal: p = 0.034).

Conclusions: Computational models predicted higher E-field delivery in the cervical SC for the C3-T3 montage. Polarity-dependent effects in motor responses were reported using this montage consistent with spinal motor modulation. tsDCS experimental protocol designs should be guided by modelling studies to improve effectiveness.

Keywords: Cervical; Computational modeling; Direct current stimulation; Neuromodulation; Spinal cord.

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Conflict of interest statement

PC Miranda is a member of the advisory board of Neuroelectrics, Barcelona, Spain.

Figures

Fig. 1
Fig. 1
Electrode settings: (a) gel, rubber pad and connector dimensions; (b) montages considered in the study, with illustration of connector configuration on the right
Fig. 2
Fig. 2
Current density magnitude distribution in a sagittal slice of the upper thoracic and neck regions for each electrode montage, with the current direction represented by grey arrows of the same length: a) C7-rD, b) C7-CMA; c) C3-T3; d) C4-CMA. Letter “A” marks the active connector position in each electrode. The magnitude colour scale is on the top right and is the same for all montages. The inset on the right of C4-CMA shows the reversal in current density direction inside the spinal canal
Fig. 3
Fig. 3
Average magnitude of the E-field and average amplitude of its components in the spinal-WM in all montages along the z axis. Position of spinal segments is marked on the grey vertical bar, electrodes are represented by vertical bars and active connectors are marked with letter “A”. Volume plots of the E-field magnitude in cervico-thoracic spinal-WM, brainstem and cerebellum are represented at the right of the average distribution in each montage, with the corresponding colour scales
Fig. 4
Fig. 4
Axial SC slices in selected cervical and T1 segments near maximum E-field peaks. Colour scale and image orientation are represented on the right
Fig. 5
Fig. 5
Boxplots of N9, N13, N18, N20 and P22 SEP’s latency for sham, anodal and cathodal conditions
Fig. 6
Fig. 6
Boxplots of upper limb MEP amplitude and latency, CSP duration, PMCT and CMCT for sham, anodal and cathodal conditions. Statistically significant differences between conditions (sham-cathodal) are marked by * (p < 0.05/3, Bonferroni corrected) in MEP latency and CMCT
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