Speakers
Description
Brain coordination is typically studied one pair at a time, yet pairwise functional connectivity cannot capture coordination among three or more regions beyond their pairwise couplings. When higher-order structure is detected, two questions remain: whether it is irreducible to its lower-order parts, and whether it is better described as a simplicial complex, a group supported by all its constituent pairwise interactions, or as a hypergraph, which carries collective structure without such support. We treat these as two poles of a single continuum fixed by the data. Each subject's resting-state fMRI (100 Human Connectome Project participants; 116 regions) is encoded as a binary bipartite network of regions and time points, a region active when its BOLD signal exceeds one standard deviation from its mean in magnitude, against which we build a hierarchy of maximum-entropy null models. A first-order model (the Bipartite Configuration Model) validates pairwise co-activations; a second-order model with nonlinear constraints (the Bipartite Partial Local Overlap Model, introduced here) validates triadic co-activations against a null preserving each region's aggregate pairwise co-activation. Significance uses one-sided Poisson–binomial tests under Benjamini–Hochberg FDR control (α=0.05). Each validated triplet is placed on a simplicial–hypergraph spectrum: a 2-simplex when its three pairs are also significant, a hyperedge when none are, mixed otherwise. Only 6.7% of candidate triplets survive; of these, 27% are simplicial, 7% hyperedges, 66% mixed. Position varies along the unimodal-to-transmodal gradient: simplices predominate in sensorimotor cortex and give way to hyperedges in limbic and subcortical systems. Along the same ordering, spatial, functional and information-theoretic signatures covary: toward the hyperedge pole triplets become spatially dispersed and functionally heterogeneous, while their O-information falls monotonically to near-zero. Simplices thus index compact, redundant coordination within functional modules, hyperedges long-range integration across them. Higher-order coordination is graded rather than dichotomous. We release the pipeline as the open-source package Trident.
| Preferred Presentation | Oral Presentation |
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