Highlights
- •Patients with DBS electrodes serve as natural models to detect electric fields inside the brain.
- •We recorded voltage changes generated by tDCS at the subthalamic level in human brain in vivo.
- •Voltage changes depend on the current level and montage of tDCS.
- •Inter-electrode spacing affected tDCS-generated voltage changes.
Abstract
Background
Transcranial direct current stimulation (tDCS) is a promising brain modulation technique
for several disease conditions. With this technique, some portion of the current penetrates
through the scalp to the cortex and modulates cortical excitability, but a recent
human cadaver study questions the amount. This insufficient intracerebral penetration
of currents may partially explain the inconsistent and mixed results in tDCS studies
to date. Experimental validation of a transcranial alternating current stimulation-generated
electric field (EF) in vivo has been performed on the cortical (using electrocorticography, ECoG, electrodes),
subcortical (using stereo electroencephalography, SEEG, electrodes) and deeper thalamic/subthalamic
levels (using DBS electrodes). However, tDCS-generated EF measurements have never
been attempted.
Objective
We aimed to demonstrate that tDCS generates biologically relevant EF as deep as the
subthalamic level in vivo.
Methods
Patients with movement disorders who have implanted deep brain stimulation (DBS) electrodes
serve as a natural experimental model for thalamic/subthalamic recordings of tDCS-generated
EF. We measured voltage changes from DBS electrodes and body resistance from tDCS
electrodes in three subjects while applying direct current to the scalp at 2 mA and
4 mA over two tDCS montages.
Results
Voltage changes at the level of deep nuclei changed proportionally with the level
of applied current and varied with different tDCS montages.
Conclusions
Our findings suggest that scalp-applied tDCS generates biologically relevant EF. Incorporation
of these experimental results may improve finite element analysis (FEA)-based models.
Keywords
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Article info
Publication history
Published online: March 13, 2018
Accepted:
March 8,
2018
Received in revised form:
February 28,
2018
Received:
December 22,
2017
Identification
Copyright
© 2018 Elsevier Inc. All rights reserved.
