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. 2023 Dec 16;13(12):2353.
doi: 10.3390/life13122353.

Transspinal Direct Current Electrical Stimulation Selectively Affects the Excitability of the Corticospinal System, Depending on the Intensity but Not Motor Skills

Alena Popyvanova  1 , Ekaterina Pomelova  1 , Dmitry Bredikhin  1 , Maria Koriakina  1 , Anna Shestakova  1 , Evgeny Blagovechtchenski  1
Affiliations

Transspinal Direct Current Electrical Stimulation Selectively Affects the Excitability of the Corticospinal System, Depending on the Intensity but Not Motor Skills

Alena Popyvanova et al. Life (Basel). .

Abstract

Transspinal direct current stimulation (tsDCS) is a non-invasive technique used to modulate spinal cord activity. However, the effects and mechanisms of this stimulation are currently not comprehensively known. This study aimed to estimate the effect of different intensities of tsDCS applied at the level of cervical enlargement of the spinal cord (C7-Th1 segments) on the excitability of the corticospinal system (CSS) and the correction of motor skills in healthy subjects. The effect of tsDCS was estimated by the motor-evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS) in the primary motor cortex (M1). The study involved 54 healthy adults aged 22 ± 4 years. The application of 11 min anodal tsDCS at the level of the cervical spine C7-Th1 with a current intensity of 2.5 mA did not change the MEP amplitude of the upper limb muscles, in contrast to the data that we previously obtained with a current intensity of 1.5 mA. We also found no difference in the effect of 2.5 mA stimulation on motor skill correction in healthy subjects in the nine-hole peg test (9-HPT) and the serial reaction time task (SRT) as with 1.5 mA stimulation. Our data show that an increase in the intensity of stimulation does not lead to an increase in the effects but rather reduces the effects of stimulation. These results provide information about the optimally appropriate stimulation current intensities to induce CSS excitability and the ability of tsDCS to influence motor skills in healthy adults.

Keywords: motor skills; non-invasive brain stimulation; transcranial magnetic stimulation; transspinal stimulation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The experimental design, consisting of two stages, each comprising four blocks. Initially, a “hot spot” search was performed for the right FDI muscle, followed by the recording of 20 MEPs induced by TMS (Tbefore). Subsequently, participants underwent 11 min of either anodal tsDCS or sham. Following the stimulation, two blocks of MEP recordings were performed: the first immediately after tsDCS (T0) and the second 15 min post-stimulation (T15). In the second stage of the study, the subjects were divided into anodal and sham groups, undergoing similar tsDCS. However, during the 11 min tsDCS session, subjects performed two motor tests—the nine-hole peg test and the serial reaction time test—aimed at evaluating manual dexterity. The impact of tsDCS was evaluated by comparing the MEP ratios before and after stimulation at both immediate and 15 min post-tsDCS intervals in both stages.
Figure 2
Figure 2
Position of electrodes. (a) General layout of TMS and tsDCS stimulating systems. Layout of electrodes: the anodal electrode was located above the C7-Th1 segment (red) and (b) the cathodal electrode was located on the clavicle (black).
Figure 3
Figure 3
Used motor tests. (A) Layout of buttons in the serial reaction time task test. The subject must press the buttons located on the response pad in accordance with the image on the screen as quickly as possible. (B) Performing the nine-hole peg test. The subject must place the pegs in 9 holes as quickly as possible and fold them back as quickly as possible.
Figure 4
Figure 4
MEP amplitudes normalized by pre-stimulation (Tbefore) values for groups receiving tsDCS (blue) and sham (gray) stimulation. The MEPs were recorded immediately after the stimulation (T0) and with a 15 min delay (T15). Markers above the columns indicate the statistical significance of the estimated marginal mean difference between corresponding MEP amplitudes before and after the tsDCS/sham session (* p < 0.05; ns: p > 0.05). Error bars represent the 95% CI of the estimates.
Figure 5
Figure 5
Performance timing of participants receiving 1.5 mA anodal tsDCS (yellow), 2.5 mA anodal tsDCS (blue), and sham (gray) stimulation assessed separately for the nine-hole peg test (9-HTP) and the serial reaction time task (SRT). No significance was observed for the Group factor, indicated by the special symbols between bars (ns: p > 0.05). Special symbols between groups of bars indicate the significance of the Day factor in each of the two ANOVA models (*** p < 0.001).
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