Fig. 2

The magnitude and radial component of the electric field induced by tDCS montages. Analysis of tDCS-induced strength and radial (normal to the cortical surface) component of the electric field (EF) using a head model (MNI152) developed from magnetic resonance imaging. Electrode montages targeting anodal tDCS in the left dorsolateral prefrontal cortex (panels A-I) and primary motor cortex (panels J-R). Anodal (red rectangle; 5 × 4 cm) and cathodal (blue rectangle; 5 × 4 cm) electrodes were placed over the scalp (A and J). The magnitude of the EF is shown in panels B-F and K-O, with hot colors (e.g., red) representing stronger EF and cold colors (e.g., blue) representing weaker EF. Panels G-I and P-R depict the radial EF, with red representing the electric current flowing into the cortex (i.e., inducing excitatory effects) and blue representing the electric current flowing out of the cortex (i.e., inducing inhibitory effects). Panels E and N show that the research montages reached the target areas with enough electric current magnitude to generate a neuromodulatory effect (blue circles roughly indicating the target locations). Furthermore, as shown in panels I and R, the target areas were stimulated with the desired polarity (i.e., anodal current) to elicit excitatory effects in the target regions (blue circles roughly indicating the target areas). Because the anatomical model for the M1 tDCS montage does not include the shoulders, the cathode electrode was placed on the lower part of the neck, which provides a good approximation of the shoulder placement. Panels show the EF magnitude and radial components in the gray matter surface (C-E, G-I, L-N, and P-R), white matter surface (F and O), and both (B and K)