Four preprocessing models were compared in the current study. All preprocessing conditions utilized the AFNI software package (Cox, 1996 (link)) and had the following series of steps in common. The first 4 EPI volumes were removed from the resting scan, and large transients in the remaining volumes were removed by constraining values to be within 4 standard deviation units of the mean (using AFNI's 3dDespike). Volumes were then slice-time corrected, co-registered to the anatomical scan, resampled to 2.0-mm isotropic voxels, smoothed with an isometric 6-mm full width half maximum Gaussian kernel, normalized by the mean signal intensity in each voxel to reflect percent signal change, and transformed into the standardized Talairach and Tournoux (1988 ) volume for the purposes of group analyses. Tissue-based nuisance regressors were created by segmenting the anatomical scan into tissue compartments using Freesurfer (Fischl et al., 2002 (link)). Ventricle and white-matter masks were created, eroding the outer voxels of the masks to prevent partial volume effects with grey matter. Eroded masks were then applied to the volume-registered EPI data (prior to smoothing) in order to yield nuisance time series with minimal contribution from gray matter signals for the ventricles, as well as a local average, at each voxel, of the EPI signal from the (eroded mask) white matter voxels within a 15 mm radius of the central voxel.
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