The impact of individual electrical fields and anatomical factors on the neurophysiological outcomes of tDCS: A TMS-MEP and MRI study

Mohsen Mosayebi-Samani; Asif Jamil; Ricardo Salvador; Giulio Ruffini; Jens Haueisen; Michael A Nitsche

doi:10.1016/j.brs.2021.01.016

The impact of individual electrical fields and anatomical factors on the neurophysiological outcomes of tDCS: A TMS-MEP and MRI study

Brain Stimul. 2021 Mar-Apr;14(2):316-326. doi: 10.1016/j.brs.2021.01.016. Epub 2021 Jan 28.

Authors

Mohsen Mosayebi-Samani¹, Asif Jamil², Ricardo Salvador³, Giulio Ruffini³, Jens Haueisen⁴, Michael A Nitsche⁵

Affiliations

¹ Department Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, Germany.
² Department Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany.
³ Neuroelectrics, Cambridge, MA (US) and Barcelona, Spain.
⁴ Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, Germany.
⁵ Department Psychology and Neurosciences, Leibniz Research Centre for Working Environment and Human Factors, Dortmund, Germany; Department of Neurology, University Hospital Bergmannsheil, Bochum, Germany. Electronic address: nitsche@ifado.de.

PMID: 33516860
DOI: 10.1016/j.brs.2021.01.016

Abstract

Background: Transcranial direct current stimulation (tDCS), a neuromodulatory non-invasive brain stimulation technique, has shown promising results in basic and clinical studies. The known interindividual variability of the effects, however, limits the efficacy of the technique. Recently we reported neurophysiological effects of tDCS applied over the primary motor cortex at the group level, based on data from twenty-nine participants who received 15min of either sham, 0.5, 1.0, 1.5 or 2.0 mA anodal, or cathodal tDCS. The neurophysiological effects were evaluated via changes in: 1) transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP), and 2) cerebral blood flow (CBF) measured by functional magnetic resonance imaging (MRI) via arterial spin labeling (ASL). At the group level, dose-dependent effects of the intervention were obtained, which however displayed interindividual variability.

Method: In the present study, we investigated the cause of the observed inter-individual variability. To this end, for each participant, a MRI-based realistic head model was designed to 1) calculate anatomical factors and 2) simulate the tDCS- and TMS-induced electrical fields (EFs). We first investigated at the regional level which individual anatomical factors explained the simulated EFs (magnitude and normal component). Then, we explored which specific anatomical and/or EF factors predicted the neurophysiological outcomes of tDCS.

Results: The results highlight a significant negative correlation between regional electrode-to-cortex distance (rECD) as well as regional CSF (rCSF) thickness, and the individual EF characteristics. In addition, while both rCSF thickness and rECD anticorrelated with tDCS-induced physiological changes, EFs positively correlated with the effects.

Conclusion: These results provide novel insights into the dependency of the neuromodulatory effects of tDCS on individual physical factors.

Keywords: CBF; Computational neurostimulation; FEM; Inter-individual variability; MEP; TMS; fMRI; tDCS.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Evoked Potentials, Motor
Humans
Magnetic Resonance Imaging
Motor Cortex* / diagnostic imaging
Transcranial Direct Current Stimulation*
Transcranial Magnetic Stimulation