In a project with investigators of NIMH, we compare cortical network architectures to human brain networks obtained using diffusion spectrum imaging (DSI) and fMRI, as well as a number of other (non-neural) weighted complex networks, like scientific collaboration networks, airline networks, etc. Our study reveals novel and robust weight organization particularly pronounced in the networks with biological origin (neural, gene), but also in different social and language (word) networks. Additionally, using simulations, we show that such network architecture can be obtained using local learning rules that adjust the weights in the network based on the past interactions between the nodes. A manuscript describing this work has been published in Nature Physics in April of 2012. Continuation of this work is under way and focuses on the learning rules. In a continuing project with investigators in the Program on Pediatric Imaging and Tissue Sciences (PPITS), NICHD we conduct a theoretical study of the observed skewed and heavy-tailed axon diamater distribution. We show that the observed distributions conforms to a heavy-tailed distribution with parametric form that optimizes the informative upper bound (IUB) as well as the information capacity. A manuscript describing this work is published in PLOS ONE in January of 2013. In a follow-up project, the distribution developed based on the optimal IUB characteristics has been implemented and applied to simulated and experimental data, yielding improved measurements of the axon diameter distributions. In a project with investigators from the Program on Pediatric Imaging and Tissue Sciences (PPITS), NICHD and the Nervous System Development and Plasticity Section, NINDS, we use the cable theory as a theoretical framework to predict how the changes in myelin thickness, as well as the increase in the nodal width, affects the propagation of the signals along a myelinated axon. Both of these are regulated by the surrounding glial cells and dependent on the level of activity present in an axon. The theoretical predictions are implemented in Mathematica and are compared with the experimentally observed values, with the ultimate goal of addressing the role of myelinating glia in learning and plasticity. Manuscript describing the experimental findings on the role of astrocytes in modifying the myelinated axon properties is about to be submitted to Neuron, while the theoretical aspect of myelin plasticity are described in a mansucript submitted to Neuroscience in July, 2013. In a new project with investigators from the Laboratory of Clinical and Developmental Genomics, NICHD we study neuronal cultures created by reprogramming skin cells from autistic patients as well as normals. It is a part of a larger study addressing the molecular and cellular changes that occur in the autistic brain during the development. In the current study the goal is to identify the changes in the network structure, or in the activity profile of different cells that distinguishes the normal cell cultures from those of autistic patients.
