, 2002). Transformation to MNI152 standard space was then further refined using FNIRT non-linear registration (Andersson et al., 2007a,b). Linear registration of each participant’s
functional time series to the space of the high-resolution structural image was also carried out using FLIRT. To control for the effects of physiological processes (such as fluctuations related to cardiac and respiratory cycles) and motion, we removed signal associated with several nuisance covariates. Specifically, we regressed each subject’s preprocessed 4-D volume on nine predictors that modeled nuisance signals from white matter, cerebrospinal fluid, the global signal and six motion parameters, as detailed elsewhere (Kelly et al., 2009). This nuisance signal regression step produced a 4-D residuals volume for each participant. As a final preprocessing step, each participant’s 4-D residuals selleck compound volume was spatially normalized by applying
the previously computed transformation to MNI152 standard space, with 1-mm3 resolution. In order to best delineate the patterns of RSFC associated with ventral area 6 and areas 44 and 45, the precise placement of the three ventrolateral frontal regions of interest (ROIs) was determined on an individual basis. Specifically, to maximize the probability that the selleck chemical ROIs would lie in architectonic areas 44, 45 and ventral area 6, we followed a two-step procedure. First, we examined each participant’s normalized (to MNI152 space) high-resolution structural MR image and used sulcal landmarks to identify the pars opercularis [Brodmann’s area (BA) 44], pars triangularis (BA 45) and the ventral part of the anterior precentral region for premotor BA 6 (described in detail below). Although the depth of the sulci may not always coincide with architectonic boundaries (Fischl et al., 2008; Lohmann et al., 2008), all studies that have examined the cytoarchitecture of the inferior frontal gyrus agree that the bulk of the pars opercularis is occupied by area 44, while the bulk of the pars triangularis is occupied by area 45 (e.g. Brodmann,
1909; Petrides & Pandya, 1994, 2002; Amunts et al., 1999). Subsequent to the initial identification step, we adjusted our placement of the ROIs according to details 5-Fluoracil of the local morphology of each particular brain. This second adjustment step was necessary in order to ensure that the ROIs would not be placed close to the sulci where there is ambiguity about the exact border between areas, but rather in a part of the pars opercularis, pars triangularis and rostral inferior precentral gyrus where all available architectonic studies agree that areas 44 and 45 and ventral area 6 are located. For instance, Amunts et al. (1999) have shown that the border of area 44 and ventral area 6 can vary within the inferior precentral sulcus.