Subgraphs of functional brain networks identify dynamical constraints of cognitive control
Fig 3
Linking functional subgraphs to neuroanatomy of canonical cognitive systems.
We uncover twelve functional subgraphs whose weighted graph edges span the 262 graph nodes specified by the brain atlas. We examine functional roles of subgraphs in cognitive processing by assigning each node to a putative cognitive system [33]: dorsal attention, default mode, frontoparietal, limbic, somatosensory, subcortical, ventral attention, visual, and cerebellum. To visualize the topology of each subgraph, we construct ring graphs in which nodes are evenly spaced around the circumference of a circle—color coded by assigned cognitive system—and edges between nodes are represented by line arcs—colored by the percentile of the edge strength in the subgraph. Subgraphs are coded A through L in decreasing order of the mean relative expression weight; subgraphs expressed more positively are represented with red letters and subgraphs expressed more negatively are represented with blue letters. For system-by-system adjacency matrix representations of functional subgraphs, we refer the reader to S5 Fig. Subgraphs reflect topological states of task-related processes whereby functional interactions within a cognitive system mark a centralized network core of information that may be shared with other cognitive systems located in the network periphery. To identify core-periphery structure for a subgraph, we compute the relative difference between the mean weight of edges adjoining nodes within a cognitive system and the mean weight of edges adjoining nodes from that cognitive system to other cognitive systems—values closer to +1 indicate stronger edges within a cognitive system than between cognitive systems (core), values closer to −1 indicate stronger edges between cognitive systems than within a cognitive system (periphery), and values closer to 0 indicate equally strong edges within and between cognitive systems (core-periphery). We observe a significant positive relationship between a subgraph’s core-periphery index and its mean relative expression across task blocks and subjects (Spearman’s ρ, ρ = 0.76, p = 0.004), suggesting that subgraph topology is closely linked with subgraph dynamics. Specifically, subgraphs that exhibit greater core and core-periphery structure express more correlated dynamics (positive; red) and subgraphs that exhibit greater periphery structure express more anticorrelated dynamics (negative; blue). These results imply that subgraphs may represent putative stages of cognitive control in which correlated dynamics correspond to integrated information processes within and across cognitive systems and anticorrelated dynamics correspond to segregated information processes between different cognitive systems. For a detailed comparison of core-periphery structure across cognitive systems and subgraphs, we refer the reader to S6 Fig.