Significant group-level hotspots found in deep brain regions during transcranial direct current stimulation (tDCS): A computational analysis of electric fields

•Novel neuroanatomical atlas of tDCS-generated electric fields on deep brain regions.•Significant group-level dosage hotspots appeared in deep brain regions during tDCS.•Analysis of electric field show that direct modulation of deep regions is feasible. Transcranial direct current stimulation (tDCS) is a neuromodulation scheme that delivers a small current via electrodes placed on the scalp. The target is generally assumed to be under the electrode, but deep brain regions could also be involved due to the large current spread between the electrodes. This study aims to computationally evaluate if group-level hotspots exist in deep brain regions for different electrode montages. We computed the tDCS-generated electric fields (EFs) in a group of subjects using interindividual registration methods that permitted the projection of EFs from individual realistic head models (n = 18) to a standard deep brain region. The spatial distribution and peak values (standard deviation of 14%) of EFs varied significantly. Nevertheless, group-level EF hotspots appeared in deep brain regions. The caudate had the highest field peaks in particular for F3-F4 montage (70% of maximum cortical EF), while other regions reach field peaks of 50%. tDCS at deeper regions may include not only modulation via underlying cortical or subcortical circuits but also modulation of deep brain regions. The presented EF atlas in deep brain regions can be used to explain tDCS mechanism or select the most appropriate tDCS montage.