Fig. 1.  Summary of region-of-interest (ROI)–based connectivity analysis procedures. (A ) Neurovascular coupling: blood oxygen level-dependent (BOLD) signal correlates with regional neural activity. In response to a local neuronal activation, regional cerebral blood flow will increase more than what is needed to supply metabolic needs. The result is an increase in blood oxygen level and an increase in T2* MRI signal (corresponding to BOLD signal). Resting-state functional MRI studies assume that region-specific low frequency BOLD signal fluctuations correspond to fluctuations in underlying neural activity; the relationship between these two variables is given by the hemodynamic response function (HRF). (B ) Single-subject (first-level) analyses procedure: extraction of individual resting-state networks. In a first step, a principal analysis decomposition of a ROI time course is performed. The first eigenvariate of this time course is then used in a correlation analysis. In each subject, single-subject analyses identify regions positively and negatively correlated (or anticorrelated) to the seed ROI time course, after removal of spurious correlations due to physiologic nonneuronal signal. Regions positively correlated to a posterior cingulate ROI are found to be part of the default network. Regions positively correlated to middle frontal gyrus are typically part of the executive-control network. Executive-control network regions are usually anticorrelated to default-network regions. (C ) Second-level analyses: computation of group level–resting state networks. Individual connectivity maps obtained at the first level are entered in a second level random effects analysis, looking for consistent correlation patterns at the group level, taking into account intersubject variability. Group results are thresholded at false discovery rate (FDR) corrected P  value less than 0.05 and rendered for display on the mean group structural MRI of the subjects. Color scale corresponds to group-level T values for each voxel. deoxyHb = deoxyhemoglobin; oxyHb = oxyhemoglobin.

Fig. 1.  Summary of region-of-interest (ROI)–based connectivity analysis procedures. (A ) Neurovascular coupling: blood oxygen level-dependent (BOLD) signal correlates with regional neural activity. In response to a local neuronal activation, regional cerebral blood flow will increase more than what is needed to supply metabolic needs. The result is an increase in blood oxygen level and an increase in T2* MRI signal (corresponding to BOLD signal). Resting-state functional MRI studies assume that region-specific low frequency BOLD signal fluctuations correspond to fluctuations in underlying neural activity; the relationship between these two variables is given by the hemodynamic response function (HRF). (B ) Single-subject (first-level) analyses procedure: extraction of individual resting-state networks. In a first step, a principal analysis decomposition of a ROI time course is performed. The first eigenvariate of this time course is then used in a correlation analysis. In each subject, single-subject analyses identify regions positively and negatively correlated (or anticorrelated) to the seed ROI time course, after removal of spurious correlations due to physiologic nonneuronal signal. Regions positively correlated to a posterior cingulate ROI are found to be part of the default network. Regions positively correlated to middle frontal gyrus are typically part of the executive-control network. Executive-control network regions are usually anticorrelated to default-network regions. (C ) Second-level analyses: computation of group level–resting state networks. Individual connectivity maps obtained at the first level are entered in a second level random effects analysis, looking for consistent correlation patterns at the group level, taking into account intersubject variability. Group results are thresholded at false discovery rate (FDR) corrected P  value less than 0.05 and rendered for display on the mean group structural MRI of the subjects. Color scale corresponds to group-level T values for each voxel. deoxyHb = deoxyhemoglobin; oxyHb = oxyhemoglobin.

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