Anatomy-informed recommendations for electrode montage and shape in electrical stimulation methods: a tDCS case study

<i>Objective.</i>Transcranial direct current stimulation (tDCS) shows potential for cognitive enhancement and neuromodulation, yet its efficacy is limited by substantial inter-individual variability in the induced electric field (<i>E</i>-field) distribution in targeting brain areas and functional networks. This study aims to develop an anatomy-informed framework to select electrode montage and geometry that optimizes network-level<i>E</i>-field delivery.<i>Approach.</i>Using high-resolution T1-weighted/T2-weighted MRI from 590 participants (ages 36-80) in the Human Connectome Project-Aging, we extracted anatomical features, including cortical, skull, and cerebrospinal fluid (CSF) thickness, and sulcal depth. We simulated<i>E</i>-fields with finite-element models (SimNIBS 4.1) across multiple commonly used montages in working memory research. Network-level analyses, based on the Schaefer atlas, were performed to assess the spatial distribution and intensity of tDCS-induced<i>E</i>-fields.<i>Main results.</i>Montage configuration and individual anatomy strongly shape the spatial distribution and intensity of tDCS-induced<i>E</i>-fields. For montages targeting the dorsolateral prefrontal cortex, the resulting fields extended beyond the intended site and exhibited considerable variability in their cortical focality and magnitude. Principal component and feature importance analyses indicated local gyrification index, cortical thickness, skull thickness, CSF thickness, and sulcal depth as primary determinants of network-level<i>E</i>-field distribution, with executive and default mode networks most consistently receiving suprathreshold<i>E</i>-field magnitudes. Importantly, peak induced<i>E</i>-field varied markedly between individuals even under standardized protocols, highlighting substantial inter-individual variability in both dosing and targeting outcomes.<i>Significance.</i>We present a practical workflow for anatomy-guided montage selection that addresses the need for personalized approaches in tDCS. This framework has the potential to improve the efficacy and reproducibility of tDCS in both research and clinical practice by accounting for individual anatomical differences in stimulation planning.