Region-of-interest-based metabolic connectivity analysis

Subject-series FDG-PET data were obtained for each group. Similar to correlations in the fMRI time-series data, Pearson's correlations were likewise calculated. The areas were defined using the AAL template. These interregional metabolic correlations were regarded as the metabolic connectivity metric (Lee et al., 2008). We calculated the metabolic connectivity matrices based on 90 brain regions using the AAL template after excluding the cerebellum.

To test the statistical significance of connectivity differences between groups, we used a non-parametric permutation test. The difference in metabolic connectivity between the 90 regions in paired groups was tested. All subjects in each group were resampled and 10,000 permutations were analyzed. Metabolic connectivity was calculated and 10,000 subtracted metabolic connectivity matrices between groups were created. Finally, an actual subtracted metabolic connectivity matrix was tested and significant differences between groups were obtained.