Presented During:
Monday, June 24, 2024: 5:45 PM - 7:00 PM
COEX
Room:
Grand Ballroom 104-105
Poster No:
105
Submission Type:
Abstract Submission
Authors:
Irtisha Chakraborty1, Rajan Kashyap2, S. Sreeraj3, Faheem Arshad4, B.K. Yamini5, Rose Bharath2, P. T. Sivakumar3, Suvarna Alladi4, Ganesan Venkatsubramanian3, T N Sathyaprabha1, Kaviraja Udupa1, Sagarika Bhattacharjee1
Institutions:
1Department of Neurophysiology, NIMHANS, Bengaluru, Karnataka, 2Department of Neuroimaging and Interventional Radiology, NIMHANS, Bengaluru, Karnataka, 3Department of Psychiatry, NIMHANS, Bengaluru, Karnataka, 4Department of Neurology, NIMHANS, Bengaluru, Karnataka, 5Speech Pathology and Audiology Department, NIMHANS, Bengaluru, Karnataka
First Author:
Co-Author(s):
Rajan Kashyap, Phd
Department of Neuroimaging and Interventional Radiology, NIMHANS
Bengaluru, Karnataka
S. Sreeraj
Department of Psychiatry, NIMHANS
Bengaluru, Karnataka
B.K. Yamini
Speech Pathology and Audiology Department, NIMHANS
Bengaluru, Karnataka
Introduction:
The variability in the effects of transcranial Direct Current Stimulation (tDCS) is seen due to the inter-individual differences in brain anatomy causing variability in the current intensity reaching the Region of Interest (ROI). Evans et al. showed that variability in current intensity within the ROI can be reduced by varying the dose (amount of current applied to the scalp) from outside the brain [3]. It is known that current intensity at target ROI also depends on montage configurations like conventional (1x1) and high-definition (HD) tDCS (4x1) as HD-tDCS is thought to be more focal [1]. The present study investigates the variability in the personalised dose needed to obtain a constant intensity at the target ROI across individuals for both HD-tDCS and Conventional tDCS. This will be investigated in dementia patients, known to have severely atrophied brains, compared against a control major depressive disorder group expected to have relatively lesser brain atrophy.
Methods:
T1 weighted MRI images of 125 subjects (78 Dementia and 47 Depression), were used to simulate 2 language pathway montages (dorsal CP5_Cz and ventral TP7_Nape of the neck) [2] using 2 montage configurations (Conventional and HD electrode) and 2mA input current through ROAST software. ROAST final output gives electric field distribution for both montages [4]. ROAST output i-SATA (MNI) software [5] estimates Average Current Density (ACD) across individual cortical lobes and gyri in two ROIs for each dorsal [Inferior parietal lobule (IPL) and angular gyrus (AG)] and ventral [middle temporal gyrus (MTG) and inferior temporal gyrus (ITG)] pathways of language (Figure 1). Using ACD data, we calculate the required dose (RD) for conventional and HD-tDCS by following formulae.[3,5]
Required Dose= 2/(simulated current at ROI )× Desired intensity at ROI
The desired intensity at the target ROI was determined as the intensity obtained at the same ROI after simulating MNI brain with 2 mA as the current dose.
DTDI (Dose-target determination index) measured the probability of target ROI receiving the maximum current, was calculated by following formulae [5]
DTDI=(ACD at the target ROI)/(Maximum value of ACD formed at any ROI)
A DTDI value of 1 show that the maximum stimulation intensity (ACD) is generated at the target ROI. However, the peak intensity may be received at non-targeted ROI, resulting in a DTDI value <1. A DTDI value of 0 will indicate no stimulation of the target ROI.
Three separate Linear regression analysis was performed to understand the relationship between the dose, ACD at ROIs and DTDI index as dependent variable and montage configuration (conventional vs HD) as the independent variable while controlling for age and sex.
Results:
For all 4 target ROIs in both the groups (dementia and depression), the ACD at ROI was significantly higher for conventional tDCS than HD-tDCS. For the dementia group, the dorsal and ventral pathway ROIs needed significantly lesser doses for conventional tDCS than HD tDCS. However, such a difference in the dosage requirement was seen only for dorsal pathway ROIs in the control depression group. The DTDI values were almost similar between the two montage configurations in both the groups, except IPL(both dementia and depression) and AG (only dementia) ROIs showed a higher probability of reaching peak current for conventional montage (Figure 2).
Conclusions:
We found that significantly higher ACD is received at the target ROI for conventional montage than HD-tDCS, consistent across different ROIs and disease groups. However, depending on the disease population (with varying degrees of atrophy), conventional tDCS requires a lower individual current dose (within the maximum tolerable dosage of 4mA) outside the scalp to generate a consistent current intensity at the target ROI across individuals. However, the probability of hitting the target region with peak current remains unchanged, irrespective of the montage configuration.
Brain Stimulation:
Non-invasive Magnetic/TMS
TDCS 1
Disorders of the Nervous System:
Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s) 2
Psychiatric (eg. Depression, Anxiety, Schizophrenia)
Language:
Language Comprehension and Semantics
Keywords:
Aphasia
Degenerative Disease
Other - tDCS simulation
1|2Indicates the priority used for review
Provide references using author date format
[1] Alam, M. (2016). 'Spatial and polarity precision of concentric high-definition transcranial direct current stimulation (HD-tDCS)', Physics in Medicine & Biology, 61(12), 4506.
[2] Bhattacharjee, S.(2019). 'Simulation analyses of tDCS montages for the investigation of dorsal and ventral pathways', Scientific reports, 9(1), 12178.
[3] Evans, C. (2020). 'Dose-controlled tDCS reduces electric field intensity variability at a cortical target site', Brain stimulation, 13(1), 125-136.4.
[4] Huang, Y. (2019). 'Realistic volumetric-approach to simulate transcranial electric stimulation—ROAST—a fully automated open-source pipeline', Journal of neural engineering, 16(5), 056006.
[5] Kashyap, R.(2021). 'Focality-oriented selection of current dose for transcranial direct current stimulation', Journal of Personalized Medicine, 11(9), 940.