Estimation of CSD was performed using surface Laplacians [96]. These methods are more sensitive than surface potentials to local brain sources [97] as they improve the spatial resolution of EEG [98]. The CSD methods have been widely employed in studying several neuropsychiatric disorders to understand the cortical sources underlying scalp potentials during resting state and during cognitive processing (for a review, see Kamarajan et al. [99]). The CSD maps were constructed from the Laplacian transformed data as described by Wang and Begleiter [100]. This method has also been applied in our earlier studies [41,101]. Since the recorded potential at each electrode represents the resultant contributions from several adjacent and distal sources, local sources cannot be clearly estimated [102]. The CSD transform acts as a spatial filter and provides an estimate of the local radial current density [96,102,103] and represents components of the primary neural activity in the scalp region [104]. In the present study, surface Laplacian was computed on the grand mean waveforms representing ERO total theta amplitude for each subgroup and for each task condition separately. The surface Laplacian
