Sagarika Bhattacharjee1, Rajan Kashyap2, Alicia M Goodwill3, Beth Ann O'Brien4, Brenda Rapp5, Kenichi Oishi6, John E Desmond7, S H Annabel Chen8. 1. Psychology, School of Social Sciences, Nanyang Technological University, Singapore. Electronic address: bhattacharya.sagarika7@gmail.com. 2. Centre for Research and Development in Learning (CRADLE), Nanyang Technological University, Singapore. Electronic address: rajankashyap6@gmail.com. 3. Centre for Research and Development in Learning (CRADLE), Nanyang Technological University, Singapore; Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang Technological University, Singapore. Electronic address: alicia.goodwill@nie.edu.sg. 4. Centre for Research in Child Development (CRCD), National Institute of Education, Singapore. Electronic address: obrienbeth1@gmail.com. 5. The Johns Hopkins University, Krieger School of Arts and Sciences, Baltimore, United States. Electronic address: brapp1@jhu.edu. 6. The Johns Hopkins University School of Medicine, Baltimore, United States. Electronic address: koishi@mri.jhu.edu. 7. The Johns Hopkins University School of Medicine, Baltimore, United States. Electronic address: jdesmon2@jhmi.edu. 8. Psychology, School of Social Sciences, Nanyang Technological University, Singapore; Centre for Research and Development in Learning (CRADLE), Nanyang Technological University, Singapore; Lee Kong Chian School of Medicine (LKC Medicine), Nanyang Technological University, Singapore. Electronic address: annabelchen@ntu.edu.sg.
Abstract
INTRODUCTION: The observed variability in the effects of transcranial direct current stimulation (tDCS) is influenced by the amount of current reaching the targeted region-of-interest (ROI). Age and sex might affect current density at target ROI due to their impact on cortical anatomy. The present tDCS simulation study investigates the effects of cortical anatomical parameters (volumes, dimension, and torque) on simulated tDCS current density in healthy young, middle-aged, and older males and females. METHODOLOGY: Individualized head models from 240 subjects (120 males, 18-87 years of age) were used to identify the estimated current density (2 mA current intensity, 25 cm2 electrode) from two simulated tDCS montages (CP5_CZ and F3_FP2) targeting the inferior parietal lobule (IPL) and middle frontal gyrus (MFG), respectively. Cortical parameters including segmented brain volumes (cerebrospinal fluid [CSF], grey and white matter), cerebral-dimensions (length/width &length/height) and brain-torque (front and back shift, petalia, and bending) were measured using the magnetic resonance images (MRIs) from each subject. The present study estimated sex differences in current density at these target ROIs mediated by these cortical parameters within each age group. RESULTS: For both tDCS montages, females in the older age group received higher current density than their male counterparts at the target ROIs. No sex differences were observed in the middle-aged group. Males in the younger age group had a higher current density than females, only for the parietal montage. Across all age groups, CSF, and grey matter volumes significantly predicted the current intensity estimated at the target sites. In the older age group only, brain-torque was a significant mediator of the sex difference. CONCLUSIONS: Our findings demonstrate the presence of sex differences in the simulated tDCS current density, however this pattern differed across age groups and stimulation locations. Future studies should consider influence of age and sex on individual cortical anatomy and tailor tDCS stimulation parameters accordingly.
INTRODUCTION: The observed variability in the effects of transcranial direct current stimulation (tDCS) is influenced by the amount of current reaching the targeted region-of-interest (ROI). Age and sex might affect current density at target ROI due to their impact on cortical anatomy. The present tDCS simulation study investigates the effects of cortical anatomical parameters (volumes, dimension, and torque) on simulated tDCS current density in healthy young, middle-aged, and older males and females. METHODOLOGY: Individualized head models from 240 subjects (120 males, 18-87 years of age) were used to identify the estimated current density (2 mA current intensity, 25 cm2 electrode) from two simulated tDCS montages (CP5_CZ and F3_FP2) targeting the inferior parietal lobule (IPL) and middle frontal gyrus (MFG), respectively. Cortical parameters including segmented brain volumes (cerebrospinal fluid [CSF], grey and white matter), cerebral-dimensions (length/width &length/height) and brain-torque (front and back shift, petalia, and bending) were measured using the magnetic resonance images (MRIs) from each subject. The present study estimated sex differences in current density at these target ROIs mediated by these cortical parameters within each age group. RESULTS: For both tDCS montages, females in the older age group received higher current density than their male counterparts at the target ROIs. No sex differences were observed in the middle-aged group. Males in the younger age group had a higher current density than females, only for the parietal montage. Across all age groups, CSF, and grey matter volumes significantly predicted the current intensity estimated at the target sites. In the older age group only, brain-torque was a significant mediator of the sex difference. CONCLUSIONS: Our findings demonstrate the presence of sex differences in the simulated tDCS current density, however this pattern differed across age groups and stimulation locations. Future studies should consider influence of age and sex on individual cortical anatomy and tailor tDCS stimulation parameters accordingly.
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