computing connectivity in source space, as compared with conventional 3-layer models of skin, skull, and brain 81. A finite element method, which allows for modeling arbitrary anisotropic conductivity profiles, was used to solve the EEG forward problem 82–84. Leadfields were calculated for sources on a regularly spaced grid with 1 cm distance covering the entire brain (3294 voxels) in Montreal Neurological Institute (MNI) space. Subject-specific 3D electrode positions were obtained with the CapTrak electrode localization tool (Brain Products GmbH, Germany) and results were aligned to the MNI template brain. Anatomical labeling of voxels was performed with NFRI functions 85 based on the automated anatomical labeling atlas 86 and automated Talairach atlas labels 87. PAC in source space was calculated in the same fashion as PAC in electrode space using circular-linear correlations. It is important to note that although source reconstruction methods allow us to sharpen our reasoning about the underlying pattern of activity generating the scalp-recorded EEG signal, such modeling carries with it several ambiguities. As a result, source estimates are not intended as strong claims about the precise spatial origins of neuronal generation, but rather as potential candidate regions with which to further investigate using methods with higher spatial
