Affiliations: [a] NeuRRo Lab, Department of Physical Medicine and Rehabilitation, Michigan Medicine, Ann Arbor, MI, USA
| [b]
Michigan Robotics Institute, University of Michigan, Ann Arbor, MI, USA
| [c]
School of Kinesiology, University of Michigan, Ann Arbor, MI, USA
| [d] Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
Correspondence:
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Corresponding author: Chandramouli Krishnan, PT, PhD, Director, Neuromuscular & Rehabilitation Robotics Laboratory (NeuRRo Lab), Department of Physical Medicine and Rehabilitation, Michigan Medicine, University of Michigan, 325 E Eisenhower Parkway (Suite 3013), Ann Arbor, MI –48108, USA. Tel.: +1 319 321 0117; Fax: +1 734 615 1770; E-mail: mouli@umich.edu.
Abstract: Background:There is a growing concern among the scientific community that the effects of transcranial direct current stimulation (tDCS) are highly variable across studies. The use of different tDCS devices and electrode sizes may contribute to this variability; however, this issue has not been verified experimentally. Objective:To evaluate the effects of tDCS device and electrode size on quadriceps motor cortical excitability. Methods:The effect of tDCS device and electrode size on quadriceps motor cortical excitability was quantified across a range of TMS intensities using a novel evoked torque approach that has been previously shown to be highly reliable. In experiment 1, anodal tDCS-induced excitability changes were measured in twenty individuals using two devices (Empi and Soterix) on two separate days. In experiment 2, anodal tDCS-induced excitability changes were measured in thirty individuals divided into three groups based on the electrode size. A novel Bayesian approach was used in addition to the classical hypothesis testing during data analyses. Results:There were no significant main or interaction effects, indicating that cortical excitability did not differ between different tDCS devices or electrode sizes. The lack of pre-post time effect in both experiments indicated that cortical excitability was minimally affected by anodal tDCS. Bayesian analyses indicated that the null model was more favored than the main or the interaction effects model. Conclusions:Motor cortical excitability was not altered by anodal tDCS and did not differ by devices or electrode sizes used in the study. Future studies should examine if behavioral outcomes are different based on tDCS device or electrode size.
