Figs. 4–7 depict a number of potential approaches to minimize the effect of these unwanted sources of shared variance. One approach would be to restrict connectivity interpretations to differential analyses. Unwanted sources of fluctuations can be removed, by orthogonalizing the seed region’s time course with an appropriate control region (Fig. 4B). Another approach of differential layer-dependent connectivity analysis is depicted in Figs. 5 and 6. Using a template matching approach refrains from interpretations of absolute connectivity strengths. Instead, it is based on the differential similarity, i.e. it quantifies which template correlates stronger with the profile. Yet another approach to minimize the effect of shared sources of unwanted variance would be to restrict interpretations of layer-dependent connectivity to asymmetric off-diagonal elements in the connectivity matrices (Fig. 7C). Common sources of physiological noise would be symmetric to the diagonal axis in both areas and can thus be identified and removed.
