Abstract:
Background: High definition Transcranial Direct Current Stimulation (HD-tDCS) is one of the most recent developments in neuro-modulation which finds its applications in treatment and research of many neurological and psychiatric disorders. HD-tDCS employs arrays of small concentric scalp electrodes for targeted, safe and cost effective stimulation of brain. HD-tDCS is an emerging technology and in-depth apprehension of the biophysical interactions is needed.
Since in-vivo observations are quite difficult during performance of the clinical trials,
computational modeling has played a vital role in the understanding and optimizing stimulation
therapies.
Objective: The aim of the study is to address the shortcomings of existing HD tDCS
computational models by constructing realistic three dimensional models with more layers and
different electrode placements.
Methodology: Finite Element (FE) models were developed from the averaged and subject
specific radiological images (Magnetic Resonance Imaging (MRI)). Using Maxwell’s, Laplace’s
and Gauss’s equation the Electric field (E-field) distribution has been assessed. Under the
influence of different electrode configurations (anode fixed at C3) and biological tissue
conductivities in a multilayer (19 layers) brain model, the electric field maps have been
examined.
Results: Most of the current was shunted in non-cortical areas due to the large impedance of the
scalp. In addition, the peak value of the induced E-field was spotted beneath the anode and the
current was mainly distributed underneath the circumference of stimulation montage. As the
current density in a brain layer tends to stay constant, the inclusion of directional conductivity
caused significant changes in E-field (Topological ~ 40% and Magnitude ~ 0.7) as compared to
isotropic models. Variations in the radius and shape of the montage brought noticeable changes
in the E-field maps. The intensity and the depth of penetration amplified when the radius was
increased. However, the spreading of fields over larger area of Head lessened their focality. The
fields became more uniform and hence the skewness decreased. The same trends were observed
when the electrode configuration was given a 450 shift in the orientation as the area under
electrodes has increased
Conclusion: The accuracy of the predicted region of interest and the dosage parametersof
stimulation can be controlled by using effective modeling and simulation approaches. Based on individual anatomy and pathological conditions, this study would be beneficial to the clinicians for planning customized HD-tDCS treatments of the patients.
