Functional connectivity density mapping

Abstract

Brain networks with energy-efficient hubs might support the high cognitive performance of humans and a better understanding of their organization is likely of relevance for studying not only brain development and plasticity but also neuropsychiatric disorders. However, the distribution of hubs in the human brain is largely unknown due to the high computational demands of comprehensive analytical methods. Here we propose a 10(3) times faster method to map the distribution of the local functional connectivity density (lFCD) in the human brain. The robustness of this method was tested in 979 subjects from a large repository of MRI time series collected in resting conditions. Consistently across research sites, a region located in the posterior cingulate/ventral precuneus (BA 23/31) was the area with the highest lFCD, which suggest that this is the most prominent functional hub in the brain. In addition, regions located in the inferior parietal cortex (BA 18) and cuneus (BA 18) had high lFCD. The variability of this pattern across subjects was <36% and within subjects was 12%. The power scaling of the lFCD was consistent across research centers, suggesting that that brain networks have a "scale-free" organization.

Fig. 1.

Spatial distribution of the lFCD superimposed on axial MRI views of the human brain (radiological convention). These maps reflect the average number of functional connections per voxel (k) across 979 subjects from 19 research sites around the world. Green labels indicate the axial distance to the origin of the stereotactic space (Montreal Neurological Institute). The lFCD reaches maximal value in posterior cingulate/ventral precuneus (red–orange). FCDM parameters: T_SNR = 50 and T_C = 0.6.

Fig. 2.

Spatial distribution of the average lFCD superimposed on the middle sagital MRI plane for all research sites (green labels) in this study (Table 2). FCDM parameters: T_SNR = 50 and T_C = 0.6.

Fig. 3.

Average spatial distribution of the first principal component (PC 1) across all research sites showing the brain regions with high lFCD variance (red–yellow: 10–30%, radiological convention). Scatter plot shows lFCD variance as a function of the principal components for each of the sessions of the New York test–retest dataset.

Fig. 4.

Spatial distribution of the rescaled lFCD (blue–red: k/k₀ = 0–10) and gFCD (blue–red: K/K₀ = 0–10) and a statistical map (orange–yellow: P_FWE-corr < 0.05; paired t test) of the significant differences between lFCD and gFCD across 34 healthy subjects from two research sites (Ontario and Baltimore), superimposed on the middle sagittal MRI view of the human brain. T_SNR = 50 and T_C = 0.6.