Differences in tDCS-induced E-fields according to Alzheimer's disease and gender: An in-silico study
Poster No:
42
Submission Type:
Abstract Submission
Authors:
Chae-Bin Song1, Cheolki Lim2, Jongseung Lee1, Donghyeon Kim1, Hyeon Seo3
Institutions:
1NEUROPHET Inc, Seoul, Republic of Korea, 2Gwangju Institute of Science and Technology, Gwangju, Republic of Korea, 3Gyeongsang National University, Gyeongsangnam-do, Republic of Korea
First Author:
Co-Author(s):
Introduction:
Alzheimer's disease is considered the most common cause of dementia [1]. Several studies reported that transcranial direct current stimulation (tDCS) could help improve cognition for patients with Alzheimer's disease (AD) [2]. Previous studies used the same montage for AD and cognitively normal individuals (CN). However, anatomical differences for individuals due to brain atrophy affect the flow of tDCS-induced current [3]. Therefore, conventional montages might not sufficiently stimulate the target area of AD. In this study, we investigated tDCS effect for both AD and CN focused on the electric field intensities within each brain region when using the same montages through simulation.
Methods:
We used 180 T1-weighted magnetic resonance images (MRIs) from Alzheimer Disease Neuroimaging Initiative (ADNI) dataset [4] for four groups (AD-females, AD-males, CN-females, CN-males). We made no statistical differences in age distribution across groups.
An anatomical head model was constructed based on each MRI. We segmented the models into gray matter (GM), white matter (WM), scalp, skull, CSF, and ventricles through our deep learning-based brain segmentation models [5, 6]. We divided GM into 68 regions based on the function of each brain region. The mesh generation was performed using CGAL version 4.0 [7]. CGAL generated segmented MRI data into 3D tetrahedral mesh based on the Delaunay triangulation method. The electrical potential induced by tDCS was determined according to the transformed Maxwell equation in static conditions and boundary conditions [8]. We used the Eigen library as a solver to calculate the tDCS-induced electric field. We assigned electrical conductivities of each region in units of S/m (GM 0.276; WM 0.126; scalp 0.465; skull 0.01; CSF 1.65; ventricles 1.65). We located electrodes in F3-Fp2 to stimulate the left rostral middle frontal gyrus (RMF) associated with cognitions.
The maximum current was analyzed through the 90th percentile to minimize errors. We analyzed statistical differences in the tDCS-induced electric field between AD and CN for each brain region. For statistical analysis, we used the parametric unpaired t-test. A p-value of less than 0.05 was considered statistically significant.
An anatomical head model was constructed based on each MRI. We segmented the models into gray matter (GM), white matter (WM), scalp, skull, CSF, and ventricles through our deep learning-based brain segmentation models [5, 6]. We divided GM into 68 regions based on the function of each brain region. The mesh generation was performed using CGAL version 4.0 [7]. CGAL generated segmented MRI data into 3D tetrahedral mesh based on the Delaunay triangulation method. The electrical potential induced by tDCS was determined according to the transformed Maxwell equation in static conditions and boundary conditions [8]. We used the Eigen library as a solver to calculate the tDCS-induced electric field. We assigned electrical conductivities of each region in units of S/m (GM 0.276; WM 0.126; scalp 0.465; skull 0.01; CSF 1.65; ventricles 1.65). We located electrodes in F3-Fp2 to stimulate the left rostral middle frontal gyrus (RMF) associated with cognitions.
The maximum current was analyzed through the 90th percentile to minimize errors. We analyzed statistical differences in the tDCS-induced electric field between AD and CN for each brain region. For statistical analysis, we used the parametric unpaired t-test. A p-value of less than 0.05 was considered statistically significant.
Results:
In all regions, the male group showed significantly lower electric field intensities than the female group regardless of disease. The electric field intensity within the ventricle was significantly higher in CN-males than in AD-males. Among the 68 subdivided regions of GM, we focused on the electric field intensities within 14 brain regions associated with cognitions (both sides of RMF, the superior temporal gyrus, the middle temporal gyrus, the inferior temporal gyrus, the insula, the parahippocampal cortex, and the entorhinal cortex) as shown in fig. 1. In females, there were no significant differences between AD and CN. AD-males showed significantly smaller intensities within the left/right superior temporal gyrus, the left/right middle temporal gyrus, and the left insula than CN-males.
·Electric field intensities within fourteen regions related to cognitions for each group
Conclusions:
We could not observe significant differences in the target area between AD and CN. However, it is well known by previous studies that not only one specific brain region but also other all anatomical characteristics affect current flows [9]. Our results showed that some regions were significantly different in the electric field intensities between AD and CN while others did not. It might be necessary to consider all brain regions that affect the electric field distribution for improving the stimulation effect. Also, the AD showed lower electric field intensities in subdivided GM regions than the CN even if not at a statistically significant level . It might be interpreted that stimulating the target area for AD when using the same montages for CN is difficult due to complex factors such as brain atrophy. We propose that montage optimization that considers anatomical variations and brain atrophy might lead to improvement of tDCS effects.
Brain Stimulation:
Non-invasive Electrical/tDCS/tACS/tRNS 1
Disorders of the Nervous System:
Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s) 2
Keywords:
Cognition
Computational Neuroscience
Cortex
Data analysis
Degenerative Disease
Modeling
MRI
Open Data
Other - tDCS, simulation
1|2Indicates the priority used for review
Provide references using author date format
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