This article aims to describe a basic protocol for combining transcranial direct current stimulation (tDCS) with proton magnetic resonance spectroscopy (1H-MRS) measurements to investigate the effects of bilateral stimulation on primary motor cortex metabolism.
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Method Article
The Use of Magnetic Resonance Spectroscopy as a Tool for the Measurement of Bi-hemispheric Transcranial Electric Stimulation Effects on Primary Motor Cortex Metabolism
In This Article
Summary
Abstract
Transcranial direct current stimulation (tDCS) is a neuromodulation technique that has been increasingly used over the past decade in the treatment of neurological and psychiatric disorders such as stroke and depression. Yet, the mechanisms underlying its ability to modulate brain excitability to improve clinical symptoms remains poorly understood 33. To help improve this understanding, proton magnetic resonance spectroscopy (1H-MRS) can be used as it allows the in vivo quantification of brain metabolites such as γ-aminobutyric acid (GABA) and glutamate in a region-specific manner 41. In fact, a recent study demonstrated that 1H-MRS is indeed a powerful means to better understand the effects of tDCS on neurotransmitter concentration 34. This article aims to describe the complete protocol for combining tDCS (NeuroConn MR compatible stimulator) with 1H-MRS at 3 T using a MEGA-PRESS sequence. We will describe the impact of a protocol that has shown great promise for the treatment of motor dysfunctions after stroke, which consists of bilateral stimulation of primary motor cortices 27,30,31. Methodological factors to consider and possible modifications to the protocol are also discussed.
Introduction
The idea of applying electricity to the human brain to modulate its activity has been studied since ancient times. In fact, writings from as early as the 11th century have been found that describe the use of the torpedo electric fish in the treatment of epileptic seizures1. Yet, it is not until recently that non-invasive brain stimulation has received widespread interest in the scientific community as it was shown to produce modulatory effects on cognitive function and motor response2. While transcranial magnetic stimulation (TMS) has been extensively studied since the early 1980's3, recent interest in transcranial direc....
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Protocol
The study was approved by the Research and Community Ethics Boards of Unité de Neuroimagerie Fonctionnelle and University of Montréal and was done in compliance with the code of ethics as stated in the Declaration of Helsinki. All subjects gave written informed consent following careful screening for MRI compatibility and were financially compensated for their participation.
1. tDCS Material
- Make sure all necessary materials are available before starting the experiment (see Figure 1 for list).
Note: Different electrode sizes are available for tDCS. For this study, two 5 x 7 cm rubber electrodes ....
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Results
Figure 6 shows the position of the VOI located on the representation of hand in M1 where all MRS measures were taken. In figure 6D, a 3D visualization shows a clear representation of the tDCS electrodes positioned on the scalp over the putative primary motor cortex. Figure 7 shows representative “EDIT OFF” and difference (“DIFF”) spectra acquired in M1. Peaks corresponding to Glx, GABA+MM as well as NAA can be clearly seen.
Figure 8
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Discussion
The present paper aimed to describe a standard protocol for combining tDCS and 1H-MRS using a 3 T scanner. In the next section, methodological factors will be discussed.
Critical Steps
Contraindications Screening
Previous to the experiment, it is crucial to screen participants for any contraindication regarding the use of tDCS and 1H-MRS. The use of the following exclusion criteria is recommended for tDCS: a psychiatric or neurologic.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
This works was supported by grants from the Canadian Institutes of Health Research and the Natural Sciences and Engineering Research Council of Canada. ST was supported by a Vanier Canada Graduate scholarship from the Canadian Institutes of Health Research. MM acknowledges the support from Biotechnology Research Center (BTRC) grant P41 RR008079 and P41 EB015894 (NIBIB), and NCC P30 NS076408.
We would like to acknowledge Romain Valabrègue (Centre de NeuroImagerie de Recherche – CENIR, Paris, France) and Brice Tiret (Centre Recherche de l’Institut Universiatire de Gériatrie (CRIUGM), Montréal, Canada; Commissariat &....
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| DC-stimulator plus | NeuroConn | 30DCS01E | MR compatible device |
| NuPrep preparation gel | Weaver and Co. | #10-61 | |
| Ten20 conductive paste | Weaver and Co. | #10-20-4 | |
| Electrode prepping pad | Grass technologies | MD0017 | 70% isopropyl alcohol and pumice |
| Saline solution | Local drugstore sample | 0.9% sodium chloride | |
| Non permanent hydro-marker | Sharpie | SHPE20WH | |
| SYNGO MR VB17 | Siemens AG | MRI software | |
| MAGNETOM Trio A Tim System | Siemens AG | MRI scanner version | |
| Matlab 2013a (Version 8.1) | MathWorks Inc | processing and analysis software | |
| LCModel 6.3 | LC MODEL inc | see: s-provencher.com |
References
- Kellaway, P. The part played by electric fish in the early history of bioelectricity and electrotherapy. Bull. Hist. Med. 20 (2), 112-137 (1946).
- Brunoni, A. R., et al. Clinical research with transcranial dir....
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