Fig. 2
a Current intensities by locations of the electrodes, according to the 10–20 system, Total Injected Current, Weighted Correlation Coefficient, and average electric field (V/m) values are presented for each Montage. b Current densities (mA/cm2) and electrodes locations, according to the 10–20 system. Sham absolute densities were up to 0.08 mA/cm2. Electrodes FC5 and AF4 did not deliver current in the sham condition. c The targets of tDCS by montages targeting the left dorsolateral prefrontal cortex (L-DLPFC) and the primary motor cortex (M1). Modeling was carried out with the ‘Stimweaver’ algorithm on a standard brain to visualize the distribution of the component of the tDCS-induced electric field normal to the cortical surface. Warmer and cooler colors represent greater positive or negative normal component (En) of electrical field, respectively. Positive (current injecting, anodes) electrodes are in red; negative electrodes (cathodes) are in blue. The montage (electrode placement and current parameters) for each stimulation condition was developed using the Stimweaver® optimization technique on a realistic template head model. The stimulation regions-of-interest (ROIs) (i.e., the left DLPFC and M1) were determined via parcellation of Brodmann areas (i.e., L-DLPFC: BA 46; SM1: BA 1–4, within the leg area). The montage was designed to facilitate the excitability of the designated ROI, while at the same time optimally distributing the injected currents to minimize potential effects elsewhere in the brain. To do so, the Stimweaver algorithm was used to optimize the component of the electric field normal to the cortical surface (i.e., En) over each ROI, as this component of the induced electric field polarizes pyramidal cells in the cortex and thus has been linked to the concurrent effects of stimulation on cortical excitability. The specific objective of each optimization was to minimize the (weighted) least-squares difference between the target En-field distribution and the modeled En induced by the tDCS. The target En-field was set to + 0.25 V/m over each designated ROI, and 0 V/m over the remaining regions