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.
Highlights
In its development, transcranial direct current stimulation is an ambitious method in clinical and cognitive neuroscience to modulate neuroplasticity
We investigate the effects of anodal transcranial direct current stimulation (tDCS) on motor cortical plasticity, as measured by amplitude changes from transcranial magnetic stimulation (TMS)-induced Motor evoked potentials (MEPs)
The main goal of this work was to assess the reproducibility of tDCS-induced effects on MEPs to measure
Summary
Transcranial direct current stimulation (tDCS) is an ambitious method in clinical and cognitive neuroscience to modulate neuroplasticity. The effects of tDCS on CSE, as reported in most cases when the subject is in a relaxed state, are polarity dependent: anodal tDCS facilitates motor cortical excitability, whereas cathodal tDCS diminishes it (Nitsche and Paulus, 2000; Nitsche and Paulus, 2001; Nitsche et al, 2003; Bikson et al, 2016; Boonstra et al, 2016; Hanley et al, 2016; Hsu et al, 2016). Long-lasting CSE elevations, as revealed by tDCS, are increasingly being used as an index of functional changes in the human motor cortex (Boonstra et al, 2016; Inukai et al, 2016)
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