Figure 5
Assortative organization of whole-brain functional networks. (a–f) Examples of functional networks derived from individual mice held at minimum density (d=0.34). (a, b) Schematic visualizations of non-assortative (a, α=0.01) and highly assortative (b, α=0.56) networks. Node position along the y axis corresponds to nodal degree. Edges are binarized. Note that, while in the assortative network nodes tended to preferentially connect to other nodes with a similar degree, connections in the non-assortative network seem random in that sense. Moreover, although the total number of edges is identical in both networks, the difference in assortativity gives rise to strikingly different topologies. (c, d) Anatomical visualizations of these same networks, viewed from the horizontal and sagittal planes (top and bottom images, respectively). These images were produced with weighted edges, which depict the strength of the functional connections. Edge colors correspond to the Fisher-transformed Z-score of the correlation coefficient between each pair of connected nodes (see color bar to the right). Only the top 34% of connections, in terms of their absolute Z-score, are depicted. Nodes are color-coded according to the different brain regions that they represent: Dark green, cortical regions; light blue, striatum; marine blue, putamen; light green, amygdala; olive, hippocampus; pink, midbrain structures; red, mammillary bodies. (e, f) Heat maps of the adjacency matrices derived from these same networks, using the same Z-score color bar as above. Regions of interest are presented according to their anatomical position along the rostrocaudal axis, so that the most rostral are assigned numbers 1 and 2 and the most caudal 26 and 27. (g) Changes in network assortativity as a function of network density. Mean network assortativity for Ahi1+/+ and Ahi1+/− mice (blue and yellow, respectively) are depicted across densities within the small-world regime. Note that Ahi1+/− mice displayed an assortative pattern across densities, compared with a non-assortative topology displayed by Ahi1+/+ mice. (f) Between-genotype differences in network assortativity as a function of network density. The 95% confidence intervals and between-group differences in assortativity are depicted. The red * marker shows the difference between Ahi1+/− and Ahi1+/+ networks; thus * signs falling above the confidence intervals indicate densities in which Ahi1+/− mean network assortativity is significantly higher than Ahi1+/+. Relative to the Ahi1+/+ networks, the assortativity coefficients of the Ahi1+/− networks were significantly higher across almost all densities. n=13 (Ahi1+/+), n=12 (Ahi1+/−).
