Standardized low-resolution brain electromagnetic tomography (sLORETA70,71) was used to estimate the intracerebral electrical sources. As a standard procedure, a common average reference transformation70 was performed before applying the sLORETA algorithm. sLORETA computes electric neuronal activity as current density (A/m2) without assuming a predefined number of active sources. The solution space used in this study and associated lead-field matrix are those implemented in the LORETA-Key software (freely available at http://www.uzh.ch/keyinst/loreta.htm). This software implements revisited realistic electrode coordinates (Jurcak et al. 2007) and the lead field produced by Fuchs et al.72 by applying the boundary element method on the MNI-152 (Montreal neurological institute, Canada) template of Mazziotta et al.73,74. The sLORETA-key anatomical template divides and labels the neocortical (including hippocampus and anterior cingulate cortex) MNI-152 volume in 6,239 voxels of dimension 5 mm3, based on probabilities returned by the Demon Atlas75,76.
