Transcranial electrical stimulation motor threshold can estimate individualized tDCS dosage from reverse-calculation electric-field modeling

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Abstract

Background:

Unique amongst brain stimulation tools, transcranial direct current stimulation (tDCS) currently lacks an easy or widely implemented method for individualizing dosage.

Objective:

We developed a method of reverse-calculating electric-field (E-field) models based on Magnetic Resonance Imaging (MRI) scans that can estimate individualized tDCS dose. We also evaluated an MRI-free method of individualizing tDCS dose by measuring transcranial magnetic stimulation (TMS) motor threshold (MT) and single pulse, suprathreshold transcranial electrical stimulation (TES) MT and regressing it against E-field modeling. Key assumptions of reverse-calculation E-field modeling, including the size of region of interest (ROI) analysis and the linearity of multiple E-field models were also tested.

Methods:

In 29 healthy adults, we acquired TMS MT, TES MT, and anatomical T1-weighted MPRAGE MRI scans with a fiducial marking the motor hotspot. We then computed a “reverse-calculated tDCS dose” of tDCS applied at the scalp needed to cause a 1.00 V/m E-field at the cortex. Finally, we examined whether the predicted E-field values correlated with each participant’s measured TMS MT or TES MT.

Results:

We were able to determine a reverse-calculated tDCS dose for each participant using a 5 × 5 x 5 voxel grid region of interest (ROI) approach (average = 6.03 mA, SD = 1.44 mA, range = 3.75–9.74 mA). The Transcranial Electrical Stimulation MT, but not the Transcranial Magnetic Stimulation MT, significantly correlated with the ROI-based reverse-calculated tDCS dose determined by E-field modeling (R ² = 0.45, p < 0.001).

Conclusions:

Reverse-calculation E-field modeling, alone or regressed against TES MT, shows promise as a method to individualize tDCS dose. The large range of the reverse-calculated tDCS doses between subjects underscores the likely need to individualize tDCS dose. Future research should further examine the use of TES MT to individually dose tDCS as an MRI-free method of dosing tDCS.

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Most cited references 77

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Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

M A Nitsche, W. Paulus (2000)

In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp. Excitability changes of up to 40 %, revealed by transcranial magnetic stimulation, were accomplished and lasted for several minutes after the end of current stimulation. Excitation could be achieved selectively by anodal stimulation, and inhibition by cathodal stimulation. By varying the current intensity and duration, the strength and duration of the after-effects could be controlled. The effects were probably induced by modification of membrane polarisation. Functional alterations related to post-tetanic potentiation, short-term potentiation and processes similar to postexcitatory central inhibition are the likely candidates for the excitability changes after the end of stimulation. Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive, painless, reversible, selective and focal way.

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Safety of Transcranial Direct Current Stimulation: Evidence Based Update 2016.

Marom Bikson, Pnina Grossman, Chris P. Thomas … (2016)

This review updates and consolidates evidence on the safety of transcranial Direct Current Stimulation (tDCS). Safety is here operationally defined by, and limited to, the absence of evidence for a Serious Adverse Effect, the criteria for which are rigorously defined. This review adopts an evidence-based approach, based on an aggregation of experience from human trials, taking care not to confuse speculation on potential hazards or lack of data to refute such speculation with evidence for risk. Safety data from animal tests for tissue damage are reviewed with systematic consideration of translation to humans. Arbitrary safety considerations are avoided. Computational models are used to relate dose to brain exposure in humans and animals. We review relevant dose-response curves and dose metrics (e.g. current, duration, current density, charge, charge density) for meaningful safety standards. Special consideration is given to theoretically vulnerable populations including children and the elderly, subjects with mood disorders, epilepsy, stroke, implants, and home users. Evidence from relevant animal models indicates that brain injury by Direct Current Stimulation (DCS) occurs at predicted brain current densities (6.3-13 A/m(2)) that are over an order of magnitude above those produced by conventional tDCS. To date, the use of conventional tDCS protocols in human trials (≤40 min, ≤4 milliamperes, ≤7.2 Coulombs) has not produced any reports of a Serious Adverse Effect or irreversible injury across over 33,200 sessions and 1000 subjects with repeated sessions. This includes a wide variety of subjects, including persons from potentially vulnerable populations.

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Variability in response to transcranial direct current stimulation of the motor cortex.

Sarah Wiethoff, Masashi Hamada, John Rothwell (2014)

Responses to a number of different plasticity-inducing brain stimulation protocols are highly variable. However there is little data available on the variability of response to transcranial direct current stimulation (TDCS). We tested the effects of TDCS over the motor cortex on corticospinal excitability. We also examined whether an individual's response could be predicted from measurements of onset latency of motor evoked potential (MEP) following stimulation with different orientations of monophasic transcranial magnetic stimulation (TMS). Fifty-three healthy subjects participated in a crossover-design. Baseline latency measurements with different coil orientations and MEPs were recorded from the first dorsal interosseous muscle prior to the application of 10 min of 2 mA TDCS (0.057 mA/cm2). Thirty MEPs were measured every 5 min for up to half an hour after the intervention to assess after-effects on corticospinal excitability. Anodal TDCS at 2 mA facilitated MEPs whereas there was no significant effect of 2 mA cathodal TDCS. A two-step cluster analysis suggested that approximately 50% individuals had only a minor, or no response to TDCS whereas the remainder had a facilitatory effect to both forms of stimulation. There was a significant correlation between the latency difference of MEPs (anterior-posterior stimulation minus latero-medial stimulation) and the response to anodal, but not cathodal TDCS. The large variability in response to these TDCS protocols is in line with similar studies using other forms of non-invasive brain stimulation. The effects highlight the need to develop more robust protocols, and understand the individual factors that determine responsiveness. Copyright © 2014. Published by Elsevier Inc.

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Author and article information

Journal

Journal ID (nlm-journal-id): 101465726

Journal ID (pubmed-jr-id): 35618

Journal ID (nlm-ta): Brain Stimul

Journal ID (iso-abbrev): Brain Stimul

Title: Brain stimulation

ISSN (Print): 1935-861X

ISSN (Electronic): 1876-4754

Publication date Nihms-submitted: 7 February 2021

Publication date (Electronic): 21 April 2020

Publication date (Print): Jul-Aug 2020

Publication date PMC-release: 25 February 2021

Volume: 13

Issue: 4

Pages: 961-969

Affiliations

[a ]Brain Stimulation Laboratory, Department of Psychiatry, Medical University of South Carolina, Charleston, SC, USA

[b ]Department of Biomedical Engineering, The City College of New York, NY, USA

[c ]Ralph H. Johnson VA Medical Center, Charleston, SC, USA

Author notes

[* ]Corresponding author. Medical University of South Carolina, Department of Psychiatry, Brain Stimulation Division, 67 President St., 502N, Charleston, SC, 29425, USA. caulfiel@ 123456musc.edu (K.A. Caulfield).

CRediT authorship contribution statement

Kevin A. Caulfield: Data curation, Formal analysis, Writing - original draft. Bashar W. Badran: Data curation, Formal analysis, Writing - original draft. William H. DeVries: Data curation, Formal analysis, Writing - original draft. Philipp M. Summers: Data curation, Formal analysis, Writing - original draft. Emma Kofmehl: Data curation, Formal analysis, Writing - original draft. Xingbao Li: Data curation, Formal analysis, Writing - original draft. Jeffrey J. Borckardt: Data curation, Formal analysis, Writing - original draft. Marom Bikson: Data curation, Formal analysis, Writing - original draft. Mark S. George: Data curation, Formal analysis, Writing - original draft.

Article

Manuscript ID: NIHMS1666634

DOI: 10.1016/j.brs.2020.04.007

PMC ID: 7906246

PubMed ID: 32330607

SO-VID: 0ab39ae5-1611-4d5d-9576-f39a58e45dcd

License:

This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/).

Transcranial electrical stimulation motor threshold can estimate individualized tDCS dosage from reverse-calculation electric-field modeling

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Abstract

Background:

Objective:

Methods:

Results:

Conclusions:

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NeuroImaging Methods

Most cited references 77

Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

Safety of Transcranial Direct Current Stimulation: Evidence Based Update 2016.

Variability in response to transcranial direct current stimulation of the motor cortex.

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