Connectivity preprocessing followed prior methods, well described and widely used in the imaging literature (Fair et al., 2007; Fair et al., 2009). These steps included: (i) a temporal band-pass filter (0.009 Hz < f <0.08 Hz), (ii) regression of six parameters obtained by rigid body head motion correction, (iii) regression of the whole brain signal averaged over the whole brain, (iv) regression of ventricular signal averaged from ventricular region of interest (ROI), and (v) regression of white matter signal averaged from white matter ROI. Regression of first order derivative terms for the whole brain, ventricular, and white matter signals were also included in the correlation preprocessing. These preprocessing steps aim to reduce spurious variance unlikely to reflect neuronal activity (Fox and Raichle, 2007).
