inverse solution against spontaneous brain oscillations, the noise covariance used for inverse calculation was estimated from the empty room data pooled across recording sessions and band-pass filtered between 3 and 50 Hz. A signal-to-noise ratio (SNR) of 5 (Lin et al., 2004) was used for scaling of the noise covariance in calculation of the inverse operator. An identity matrix was used for the noise-sensitivity normalization of the source-space solution. The noise-sensitivity normalized estimates of total source power were obtained for each frequency at each location on the cortical surface. For each subject, a map of total theta source power was calculated by averaging across frequencies and trials. Total event-related theta power estimates were then baseline corrected by subtracting the mean theta source power estimate in the 300 ms prestimulus period. Group average maps of baseline-corrected total theta power are shown in Figures 2–4.
