Dose-controlled tDCS reduces electric field intensity variability at a cortical target site

Carys Evans; Clarissa Bachmann; Jenny S A Lee; Evridiki Gregoriou; Nick Ward; Sven Bestmann

doi:10.1016/j.brs.2019.10.004

Dose-controlled tDCS reduces electric field intensity variability at a cortical target site

Brain Stimul. 2020 Jan-Feb;13(1):125-136. doi: 10.1016/j.brs.2019.10.004. Epub 2019 Oct 7.

Authors

Carys Evans¹, Clarissa Bachmann², Jenny S A Lee², Evridiki Gregoriou², Nick Ward², Sven Bestmann³

Affiliations

¹ Department for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, UK. Electronic address: carys.evans@ucl.ac.uk.
² Department for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, UK.
³ Department for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, UK; Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, UK.

PMID: 31653475
DOI: 10.1016/j.brs.2019.10.004

Abstract

Background: Variable effects limit the efficacy of transcranial direct current stimulation (tDCS) as a research and therapeutic tool. Conventional application of a fixed-dose of tDCS does not account for inter-individual differences in anatomy (e.g. skull thickness), which varies the amount of current reaching the brain. Individualised dose-control may reduce the variable effects of tDCS by reducing variability in electric field (E-field) intensities at a cortical target site.

Objective: To characterise the variability in E-field intensity at a cortical site (left primary motor cortex; M1) and throughout the brain for conventional fixed-dose tDCS, and individualised dose-controlled tDCS.

Methods: The intensity and distribution of the E-field during tDCS was estimated using Realistic Volumetric Approach to Simulate Transcranial Electric Stimulation (ROAST) in 50 individual brain scans taken from the Human Connectome Project, for fixed-dose tDCS (1 mA & 2 mA) and individualised dose-controlled tDCS targeting left M1.

Results: With a fixed-dose (1 mA & 2 mA), E-field intensity in left M1 varied by more than 100% across individuals, with substantial variation observed throughout the brain as well. Individualised dose-control ensured the same E-field intensity was delivered to left M1 in all individuals. Its variance in other regions of interest (right M1 and area underneath the electrodes) was comparable with fixed- and individualised-dose.

Conclusions: Individualised dose-control can eliminate the variance in E-field intensities at a cortical target site. Assuming that the current delivered to the brain directly determines its physiological and behavioural consequences, this approach may allow for reducing the known variability of tDCS effects.

Keywords: Brain stimulation; Current flow model; Individualization; Inter-individual variability; Transcranial electrical stimulation.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Adult
Biological Variation, Population*
Brain Waves
Evoked Potentials, Motor
Female
Humans
Male
Models, Neurological
Motor Cortex / physiology*
Random Allocation
Transcranial Direct Current Stimulation / methods*
Transcranial Direct Current Stimulation / standards