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. 2019 Jul;7(13):e14087.
doi: 10.14814/phy2.14087.

Effects of anodal transcranial direct current stimulation on motor evoked potentials variability in humans

Shahid Bashir  1 , Shafiq Ahmad  2 , Moath Alatefi  2 , Ali Hamza  3 , Mohamed Sharaf  2 , Shirely Fecteau  4 , Woo Kyoung Yoo  5   6
Affiliations

Effects of anodal transcranial direct current stimulation on motor evoked potentials variability in humans

Shahid Bashir et al. Physiol Rep. 2019 Jul.

Abstract

Motor evoked potentials (MEPs) obtained from transcranial magnetic stimulation (TMS) allow corticospinal excitability (CSE) to be measured in the human primary motor cortex (M1). CSE responses to transcranial direct current stimulation (tDCS) protocols are highly variable. Here, we tested the reproducibility and reliability of individual MEPs following a common anodal tDCS protocol. In this study, 32 healthy subjects received anodal tDCS stimulation over the left M1 for three durations (tDCS-T5, tDCS-T10, and tDCS-T20 min) on separate days in a crossover-randomized order. After the resting motor threshold (RMT) was determined for the contralateral first dorsal interosseous muscle, 15 single pulses 4-8 sec apart at an intensity of 120% RMT were delivered to the left M1 to determine the baseline MEP amplitude at T0 , T5 , T10 , T20 , T30 , T40 , T50 , and T60 min after stimulation for each durations. During TMS delivery, 3D images of the participant's cortex and hot spot were visualized for obtaining MEPs from same position. Our findings revealed that there was a significant MEPs improvement at T0 (P = 0.01) after 10 min of anodal stimulation. After the 20-min stimulation duration, MEPs differed specifically at T0, T5, T30 min (P < 0.05). This indicates that tDCS is a promising tool to improve MEPs. Our observed variability in response to the tDCS protocol is consistent with other noninvasive brain stimulation studies.

Keywords: Corticospinal excitability; Motor cortex; Motor evoked potentials; Resting motor threshold; Transcranial direct current stimulation.

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Conflict of interest statement

The author(s) declare(s) that there is no conflict of interest regarding the publication of this paper.

Figures

Figure 1
Figure 1
Region of interest (ROI) selected from the motor cortex strip from both hemisphere for the correlation analysis of cortical thickness and motor evoked potentials.
Figure 2
Figure 2
Mean motor evoked potentials (MEPs) from the left hemisphere of 32 subjects representing by each axis with respect to tDCS‐T5_baseline and follow‐up MEPs assessment at time point, T 0, T 5, T 10, T 20, T 30, T 40, T 50, and T 60 min.
Figure 3
Figure 3
Mean motor evoked potentials (MEPs) from the left hemisphere of 32 subjects representing by each axis with respect to tDCS‐T10_baseline and follow‐up MEPs assessment at time point, T 0, T 5, T 10, T 20, T 30, T 40, T 50, and T 60 min.
Figure 4
Figure 4
Mean motor evoked potentials (MEPs) from the left hemisphere of 32 subjects representing by each axis with respect to tDCS‐T20_baseline and follow‐up MEPs assessment at time point, T 0, T 5, T 10, T 20, T 30, T 40, T 50, and T 60 min.
Figure 5
Figure 5
Mean motor evoked potentials (MEPs) at baseline and follow‐up MEPs assessment at time point, T 0, T 5, T 10, T 20, T 30, T 40, T 50, and T 60 min for tDCS‐T5, tDCS‐T10 and tDCS‐T20. The bar graph showed confidence limit the bars reflect (standard deviation).
Figure 6
Figure 6
The grand average value expressed as the percentage of “responders” (favorable MEP increase after anodal tic's stimulation) and “non‐responders” using the mean grand average poststimulation criterion. Subjects with grand averages > 1 were classified as “non‐responders” and subjects with grand averages < 1 were classified as “responders” for tDCS‐T5, tDCS‐T10, and tDCS‐T20 min.
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