title: Resolving structural variability in network models and the brain.
abstract: Large-scale white matter pathways crisscrossing the cortex create a complex pattern of connectivity that underlies human cognitive function. Generative mechanisms for this architecture have been difficult to identify in part because little is known in general about mechanistic drivers of structured networks. Here we contrast network properties derived from diffusion spectrum imaging data of the human brain with 13 synthetic network models chosen to probe the roles of physical network embedding and temporal network growth. We characterize both the empirical and synthetic networks using familiar graph metrics, but presented here in a more complete statistical form, as scatter plots and distributions, to reveal the full range of variability of each measure across scales in the network. We focus specifically on the degree distribution, degree assortativity, hierarchy, topological Rentian scaling, and topological fractal scaling--in addition to several summary statistics, including the mean clustering coefficient, the shortest path-length, and the network diameter. The models are investigated in a progressive, branching sequence, aimed at capturing different elements thought to be important in the brain, and range from simple random and regular networks, to models that incorporate specific growth rules and constraints. We find that synthetic models that constrain the network nodes to be physically embedded in anatomical brain regions tend to produce distributions that are most similar to the corresponding measurements for the brain. We also find that network models hardcoded to display one network property (e.g., assortativity) do not in general simultaneously display a second (e.g., hierarchy). This relative independence of network properties suggests that multiple neurobiological mechanisms might be at play in the development of human brain network architecture. Together, the network models that we develop and employ provide a potentially useful starting point for the statistical inference of brain network structure from neuroimaging data.
authors.affiliation: Department of Physics, University of California, Santa Barbara, Santa Barbara, California, United States of America; Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany; Department of Mathematics, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Florian
authors.initials: F
authors.lastname: Klimm
authors.affiliation: Department of Physics, University of California, Santa Barbara, Santa Barbara, California, United States of America; Sage Center for the Study of the Mind, University of California, Santa Barbara, Santa Barbara, California, United States of America; Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvannia, United States of America.
authors.forename: Danielle S
authors.initials: DS
authors.lastname: Bassett
authors.affiliation: Department of Physics, University of California, Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Jean M
authors.initials: JM
authors.lastname: Carlson
authors.affiliation: Department of Mathematics, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America; Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Mucha
mesh_terms: D000465:Algorithms; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000502:physiology; D016000:Cluster Analysis; D019295:Computational Biology; D017709:Fractals; D064368:Healthy Volunteers; D006801:Humans; D008959:Models, Neurological; D015233:Models, Statistical; D009415:Nerve Net / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D011336:Probability; D012984:Software