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Updated: Jan 9, 2026
Neuronavigated Focalized Transcranial Direct Current Stimulation Administered During Functional Magnetic Resonance Imaging
Published on: November 15, 2024
Group-level and personalized optimization for the insula and hippocampus focal electric field in transcranial
Taiga Inoue1, Naofumi Otsuru2, Akimasa Hirata3
1Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, 466-8555, Japan.
Objectives:
This study evaluated the efficacy of transcranial temporal interference stimulation (tTIS) for focal stimulation of the insula and hippocampus, which are clinically relevant but anatomically challenging targets. Individualized and group-level electrode optimizations were compared to determine whether generalized montages can provide reliable targeting while reducing the modeling demands.
Methods:
Sixty high-resolution anatomical head models (30 individuals and their mirrored counterparts) were constructed from T1-and T2-weighted magnetic resonance images. The electric field (EF) distributions were determined using the scalar-potential finite difference method. The electrode montages and current ratios were optimized to minimize the root-mean-square error between the simulated and target EF envelope (EFE) distributions. A stimulation threshold of 0.3 V/m was applied. Subsampling analysis was performed to estimate the number of head models required for stable group-level results.
Results:
For insular targeting, a novel montage combining T7-P7 and Fp1-Fp2 achieved the highest focality. The focality was comparable to most individualized configurations and reduced interindividual variability. For hippocampal targeting, a newly proposed montage combining F7-T7 and T8-P8 yielded the best group-level focality. However, individualized optimization was required in a subset of cases to achieve adequate off-target suppression. Reliable group-level EF patterns were obtained using ∼20 models for the insula and ∼9 for the hippocampus.
Conclusions:
The findings show optimal transcranial stimulation montages depend on the target's anatomical depth. For cortical targets, including deep areas like the insula, group-level montages derived from sufficiently diverse anatomical models can achieve both high focality and applicability. However, for subcortical targets like the hippocampus, individualized optimization is recommended to maximize focality and minimize off-target activation, despite requiring fewer models to achieve stable group-level patterns.
