I found a paper by Grecius et. al. (2004) "Default-mode network activity distinguishes Alzheimer's disease from healthy aging: Evidence from functional MRI", which seems to provide an explanation of spatial correlation:

"Next, a template of the default-mode network was used to select the "best-fit" of the remaining low-frequency components in each subject. To do this, we developed a nonlinear template-matching procedure that involved taking the average z score of voxels falling within the template minus the average z score of voxels outside the template and selecting the component in which this difference (the goodness of fit) was the greatest. z scores here reflect the degree to which a given voxel's time series correlates with the time series corresponding to the specific ICA component."

The paper has been cited close to 3500 times so I suppose it serves as a guide in the lierature. Is this the approach adopted by CONN? I have searched in the forum and could only find this question from last year, which was unaswered.