Determinants of the electric field during transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) continues to demonstrate success as a medical intervention for neurodegenerative diseases, psychological conditions, and traumatic brain injury recovery. One aspect of tDCS still not fully comprehended is the influence of the tDCS electric field on neural functionality. To address this issue, we present a mathematical, multiscale model that couples tDCS administration to neuron electrodynamics. We demonstrate the model’s validity and medical applicability with computational simulations using an idealized two-dimensional domain and then an MRI-derived, three-dimensional human head geometry possessing inhomogeneous and anisotropic tissue conductivities. We exemplify the capabilities of these simulations with real-world tDCS electrode configurations and treatment parameters and compare the model’s predictions to those attained from medical research studies. The model is implemented using efficient numerical strategies and solution techniques to allow the use of fine computational grids needed by the medical community.

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High-Definition Transcranial Direct Current Stimulation Improves Delayed Memory in Alzheimer’s Disease Patients: A Pilot Study Using Computational Modeling to Optimize Electrode Position

Journal of Alzheimer s Disease ◽

10.3233/jad-210378 ◽

2021 ◽

pp. 1-17

Author(s):

Ingrid Daae Rasmussen ◽

Nya Mehnwolo Boayue ◽

Matthias Mittner ◽

Martin Bystad ◽

Ole K. Grnli ◽

...

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Electric Field ◽

Computational Modeling ◽

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Cortical Atrophy ◽

Brain Anatomy ◽

High Definition ◽

Direct Current Stimulation

Background: The optimal stimulation parameters when using transcranial direct current stimulation (tDCS) to improve memory performance in patients with Alzheimer’s disease (AD) are lacking. In healthy individuals, inter-individual differences in brain anatomy significantly influence current distribution during tDCS, an effect that might be aggravated by variations in cortical atrophy in AD patients. Objective: To measure the effect of individualized HD-tDCS in AD patients. Methods: Nineteen AD patients were randomly assigned to receive active or sham high-definition tDCS (HD-tDCS). Computational modeling of the HD-tDCS-induced electric field in each patient’s brain was analyzed based on magnetic resonance imaging (MRI) scans. The chosen montage provided the highest net anodal electric field in the left dorsolateral prefrontal cortex (DLPFC). An accelerated HD-tDCS design was conducted (2 mA for 3×20 min) on two separate days. Pre- and post-intervention cognitive tests and T1 and T2-weighted MRI and diffusion tensor imaging data at baseline were analyzed. Results: Different montages were optimal for individual patients. The active HD-tDCS group improved significantly in delayed memory and MMSE performance compared to the sham group. Five participants in the active group had higher scores on delayed memory post HD-tDCS, four remained stable and one declined. The active HD-tDCS group had a significant positive correlation between fractional anisotropy in the anterior thalamic radiation and delayed memory score. Conclusion: HD-tDCS significantly improved delayed memory in AD. Our study can be regarded as a proof-of-concept attempt to increase tDCS efficacy. The present findings should be confirmed in larger samples.

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