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. 2022 Dec 8:16:1041932.
doi: 10.3389/fnins.2022.1041932. eCollection 2022.

Lumbar trans-spinal direct current stimulation: A modeling-experimental approach to dorsal root ganglia stimulation

Mariana Pereira  1 , Sofia Rita Fernandes  1   2 , Pedro Cavaleiro Miranda  2 , Mamede de Carvalho  1   3
Affiliations

Lumbar trans-spinal direct current stimulation: A modeling-experimental approach to dorsal root ganglia stimulation

Mariana Pereira et al. Front Neurosci. .

Abstract

Introduction: The excitability of spinal motor neurons (MN) can be altered through subthreshold currents, such as transcutaneous spinal direct-current stimulation (tsDCS). Current evidence shows that tsDCS can interfere with ascending somatosensory pathways and lower motor neurons' (LMN) excitability, which points to its therapeutic potential for repairing altered spinal responses. We aim to define the best tsDCS montage for maximizing the electric field (E-field) in the lumbar spinal cord (L-SC) by computer modeling; and to apply this montage to measure the effect on LMN excitability and somatosensory evoked potentials (SSEP).

Methods: A human volume conductor model was obtained from an available database. The E-field distribution was calculated considering three different electrode settings aiming at maximizing the field at L-SC and right dorsal root ganglia (DRG). The best electrode setting was then selected and applied in a blind crossover pseudo-randomized study including 14 subjects. tsDCS was delivered for 15 min (cathodal vs. sham) over L2 vertebra level (4 mA, 144 mC/cm2), and its effect on F-waves, H-reflex (including homosynaptic depression, HD) and SSEPs was investigated in the lower limbs.

Results: All simulated montages showed higher current density and E-field magnitudes between the electrodes (>0.15 V/m), with a major longitudinal component and with rostral-caudal direction. The induced E-field involved the sensory ganglia and was maximum in the right T8-left L2 montage, which was the one selected for the experimental protocol. We disclosed a statistically significant increase of the H-reflex amplitude at 0.1 Hz, after cathodal tsDCS (c-tsDCS) on both sides. No other significant change was observed.

Discussion: Our results can suggest the c-tsDCS applied to the L-SC and DRG can modulate synaptic efficiency increasing lower motor neurons response to Ia fibers excitation. The possible implications of our findings for treating clinical conditions will be addressed in future studies.

Keywords: computational modeling; dorsal ganglia; electric field; neurophysiology; spinal cord; tsDCS.

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Conflict of interest statement

PM is a member of the advisory board of Neuroelectrics, Barcelona, Spain. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Electrode montages considered in this report: (A) pvT8 left-pvL2 right; (B) T8-L2; (C) pvT8 right-pvL2 left. (D) Relative position of the active connectors in all montages.
FIGURE 2
FIGURE 2
Study design.
FIGURE 3
FIGURE 3
Average electric field (E-field) magnitude in the spinal cord (SC) (V/m) in 1 mm thick transverse slices along the z direction in the three montages: (A) spinal gray matter (spinal-GM); (B) spinal white matter (spinal-WM). The positions of the spinal segments along the SC are indicated in the vertical axis.
FIGURE 4
FIGURE 4
Average electric field (E-field) longitudinal component (V/m) in 1 mm thick transverse slices along the z direction in the three montages: (A) spinal gray matter (spinal-GM); (B) spinal white matter (spinal-WM). Spinal segments positions along the spinal cord (SC) are indicated in the vertical axis.
FIGURE 5
FIGURE 5
Electric field (E-field) magnitude distribution in transverse slices of the spinal cord (SC). The orientation of the slices is represented in the bottom left corner and color scale in V/m is represented on the right.
FIGURE 6
FIGURE 6
Electric field (E-field) magnitude distribution in the spinal dura and roots for T8 left—L2 right montage (A) and T8 right—L2 left montage (B). For each montage, a coronal view of the magnitude on the spinal dura is represented on the left and a sagittal view of spinal dura and vertebra near the L2 electrode position on the right. A color scale for the E-field magnitude is presented in the center.
FIGURE 7
FIGURE 7
Electric field (E-field) magnitude distribution and direction in transverse slices of the spinal cord (SC) at the levels of the lumbar dorsal ganglia. The orientation of the slices is shown in the bottom left corner and color scale in V/m is represented on the right. E-field direction is indicated by black arrows of the same length.
FIGURE 8
FIGURE 8
Soleus H-Reflex elicited at 0.1 Hz in the two conditions [Sham and c-tsDCS for the two types of intervention (sham–blue trace and cathodal—red trace)]. H-reflex was obtained in the soleus muscle, for the both sides. [H-mean/H1 at 0.1 Hz (%)—size of mean reflex evoked (%) of mean reflex evoked at 0.1 HZ]. *A statistically significant difference (p < 0.05).
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