All areal subgraphs with fewer than 4 members are colored white, and all modified voxelwise subgraphs with fewer than 100 voxels are colored white. Note the similarity of subgraph assignments beteween networks, despite the great difference in network size and cortical coverage, even in different subjects (main vs replication cohorts).
Bottom: subgraphs from three thresholds are shown for the areal (spheres) and modified voxelwise graphs (surfaces).
The standard measure of subgraph similarity, normalized mutual information, between node assignments of the cohorts at identical tie densities ranged from 0.86-0.92, indicating highly similar patterns across cohorts (1 = identical assignments, 0 = no information shared between assignments). ROI ordering is identical, and all subgraphs with fewer than 4 members are colored white.
Top right: for both cohorts, plots are shown of the areal assignments into subgraphs (colors) at tie densities from 10% down to 2% in 1% steps. Top left: a spring embedded layout of the areal graph at 4% tie density visualizing the graph and the basis for subgraphs. The modified voxelwise graph also reveals spatial motifs in the patterning of systems across the cortex.Ĭopyright © 2011 Elsevier Inc. Further, graph measures of the areal network indicate that the default mode subgraph shares network properties with sensory and motor subgraphs: it is internally integrated but isolated from other subgraphs, much like a "processing" system. Other subgraphs lack established functional identities we suggest possible functional characteristics for these subgraphs. These graphs contain many subgraphs in good agreement with known functional brain systems. We propose two novel brain-wide graphs, one of 264 putative functional areas, the other a modification of voxelwise networks that eliminates potentially artificial short-distance relationships. Here we study graphs of functional brain organization in healthy adults using resting state functional connectivity MRI. This work represents a significant step forward in our ability to appreciate the fundamental process of myelination, and provides the first ever in vivo visualization of myelin maturation in healthy human infancy.Real-world complex systems may be mathematically modeled as graphs, revealing properties of the system. Our results also offer preliminary evidence of hemispheric myelination rate differences. Using a new myelin-specific MRI technique, we report a spatiotemporal pattern beginning in the cerebellum, pons, and internal capsule proceeding caudocranially from the splenium of the corpus callosum and optic radiations (at 3-4 months) to the occipital and parietal lobes (at 4-6 months) and then to the genu of the corpus callosum and frontal and temporal lobes (at 6-8 months). Here we present the first quantitative study of myelination in healthy human infants, from 3 to 11 months of age. Consequently, observed signal changes are ambiguous, hindering meaningful inferences between imaging findings and metrics of learning, behavior or cognition. Although these techniques offer insight into structural maturation, they reflect several different facets of development, e.g., changes in axonal size, density, coherence, and membrane structure lipid, protein, and macromolecule content and water compartmentalization. Despite this critical role, quantitative visualization of myelination in vivo is not possible with current neuroimaging techniques including diffusion tensor and structural magnetic resonance imaging (MRI). The development of the myelin sheath enables rapid synchronized communication across the neural systems responsible for higher order cognitive functioning. Myelination, the elaboration of myelin surrounding neuronal axons, is essential for normal brain function.