Figure 1.
Functional inhomogeneity of the anatomy-based parcellation and its effects on functional connectivity.
(A) Four subregions within a precentral gyrus showed different fMRI time activities. (B) Mean time series of the precentral gyrus and calcarine sulcus have low correlation (Z=0.3), but there exist several significant correlations among subregions of them. (C) Mean time series of the precentral gyrus and visual cortex had high correlation (Z=3.49), but in reality there exist only low correlations among smaller subregions when each anatomically defined brain region were broken into smaller subregions by modularity optimization.
Figure 2.
Description of AHMO and random seeding method.
AHMO applies voxel-level modularity optimization for each individual region in an anatomical atlas, while random seeding method assigns pre-defined number of seeds to random location within a region and grows the seeds with maximally uniform size until the whole region is populated with the seed clusters (Zalesky et al., 2010). Colors for visualization were selected by algorithm developed by the BrainCOLOR project (http://www.braincolor.org/). Note that AHMO maintains the initial AAL ROI contiguity.
Figure 3.
Biased estimation of functional connectivity and graph theoretical properties in the AAL.
(A) Elements in upper- and lower- triangular matrix represent functional connectivity maps (adjacency maps) using the AAL and AHMO (regionally averaged corresponding to the AAL map). (B) Functional connectivity difference between the AAL and AHMO. (C) Statistical difference in nodal strength and betweenness centrality between the AAL-based network and AHMO-based network. (D) Global and local efficiency are lower in the AAL than in the AHMO, while mean clustering coefficient is higher in the AAL than in the AHMO. Significance was determined at p<0.05 (Bonferroni corrected for all comparisons).
Figure 4.
Nodal properties of regions within regions associated with the default mode network.
(A) Comparisons of normalized strength and betweenness centrality between AAL and AHMO. Star (*) represents significant difference (P<0.05, Bonferroni corrected for all comparisons). (B) Linearity of strength and betweenness centrality between AAL and AHMO. Dotted line (---) represents significant correlation (R=0.28; P<0.05, Bonferroni corrected for all comparisons). ACC.L: the left anterior cingulate cortex, ACC.R: the right anterior cingulate cortex, PCC.L: the left posterior cingulate cortex, PCC.R: the right posterior cingulate cortex, HP.L: the left hippocampus, HP.R: the right hippocampus, IPL.L: the left inferior parietal lobule, IPL.R: the right inferior parietal lobule, SMG.L: the left supramarginal gyrus, SMG.R: the right supramarginal gyrus, ANG.L: the left angular gyrus, ANG.R: the right angular gyrus, PRCU.L: the left precuneus, PRCU.R: the right precuneus.
Figure 5.
Linearity between AAL and AHMO according to network-forming thresholds.
At different network-forming thresholds of Z=0, 1, 2, and 3, the AAL-based and AHMO-based approaches showed significant linearity in nodal strengths in all regions except for betweenness centrality in some regions. Global and local properties showed high linearity between the AAL and AHMO methods regardless of different thresholds of Z=0, 1, 2, and 3.
Figure 6.
Sex-atlas interactions and functional connectivity maps from the posterior cingulate subregion.
(A) Although we did not find any interaction effect in functional connectivity and in global properties (P>0.005), we found a tendency towards interaction between sex and atlas in nodal properties in some brain regions (P<0.005, uncorrected) and significant interactions at the left insula (p<0.05, Bonferroni corrected for all comparisons) in betweenness centrality. They include the left precentral gyrus (PrCG), right supplementary motor area (SMA), right precuneus (PRCU), and right putamen (PUT) in nodal strength and the left middle orbitofrontal cortex (OFCmid), the triangular part of right inferior frontal gyrus (IFGtr), left insula (INS), and left calcarine sulcus (CAL) in betweenness centrality. (B) Subregions that are temporally correlated with a subregion within the posterior cingulate cortex in the AHMO.
Figure 7.
Homogeneity difference and its effect on global properties.
(A) Comparison of three atlases (AAL, AHMO and random seeding methods (RS) with different node sizes (RS137, RS184, RS231, RS231, RS372) in terms of mean within-cluster homogeneity and global and local efficiencies and mean clustering coefficients (CC). (B) Results of individual homogeneity and global and local efficiencies for the AAL, RS, and AHMO.When we compared the methods for representing regional time series, we found very high correlation between using the first eigenvariate and the regionally averaged time series (mean correlation coefficient between two time series for all ROIs were distributed from 0.76 (p = 7e-75) to 0.94 (p = 8e-100)). Therefore, we conducted all the comparison in the current study using regionally averaged time series.