2.1.2. EEG forward modeling

The electrodes were placed according to the standard 32-channel (also 64-channel in one example) 10–20 system, using the template provided in the Fieldtrip toolbox.²⁵ The locations of the electrodes are shown in Fig. 1. The resistances of the four layers were assumed to have a ratio of (from scalp to brain) 1:80:1/5:1 according to literature.²⁶ The leadfield matrix was then calculated in Fieldtrip using the SimBio toolbox.^27,28 Finally, at each dipole location, the 3D leadfield vector given by Fieldtrip was projected onto the direction normal to the cortical surface.

Placement of EEG electrodes and and DOT probes. Black dots: EEG electrodes; blue dots: DOT detectors; red dots: DOT sources; dashed lines: DOT channels formed by source-detector pairs.