In a project with investigators from the Nervous System Development and Plasticity Section, NICHD, and the Program on Pediatric Imaging and Tissue Sciences (PPITS), NICHD we study dynamic regulation of myelin by the surrounding glial cells and show that it is dependent on the level of activity present in an axon. The larger context here is to elucidate the biological mechanisms by which such regulation happens. Our role is to use 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. These theoretical predictions are implemented in Mathematica and its predictions, based on the experimentally observed structural changes are compared with the experimentally measured conduction speeds, obtained using a data analysis framework we implemented, which showed good agreement with the theory. Manuscript describing a detailed experimental findings and the mechanism of the dynamic myelin regulation by the astrocytes is to be submitted to Neuron. We also developed different models of myelin plasticity, or generally, delay plasticity. We study the consequences of such adaptive time delays for two main cases: one where the plasticity is activity dependent and another where the plasticity depends on the temporal mismatch between presynaptic and postsynaptic action potentials. In the former case, we studied the effect of activity dependent adaptive time delays on the stability of the system of coupled oscillators, with implications to the stability of the oscillations and synchrony in the brain. In a manuscript published in Neuroscience in September of 2014, we showed how the impairment of activity-dependent myelination and the loss of adaptive time delays may contribute to disorders where hyper- and hypo-synchrony of neuronal firing leads to dysfunction (e.g., dyslexia, schizophrenia, epilepsy). This suggests that the myelin plasticity may be necessary to maintain normal oscillatory activity in the developing and adult brain. This work was presented at the Annual Meeting of the Society for Neuroscience, Washington, D.C., in November of 2014. Newly proposed models of delay plasticity based on temporal mismatch were studied in the context of spiking neural networks. We show how the stability of the synchronized state in the network relies on having adaptive delay. This work is to be presented at the Annual Meeting of the Society for Neuroscience in Chicago, IL, in October of 2015. In a project with investigators of the Section on Critical Brain Dynamics in the Intramural Research Program at NIMH, we study weighted complex networks, in particular cortical and brain networks. 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. We conducted a detailed simulation study of this learning rule, which is reminiscent of temporal delay reinforcement learning. We show that such type of learning increases the accessibility of all paths on the network and allows such complex systems to overcome engrained structure/paths and allows it to adapt to new challenges. This work has been published in the Journal of Complex Networks in March of 2015. In a project with investigators in the Program on Pediatric Imaging and Tissue Sciences (PPITS), NICHD and the section on Critical Brain Dynamics in the Intramural Research Program at NIMH, we conduct an experimental study aiming to answer questions about the possibility of detecting neural activity directly using MRI on NMR measurements. A new experimental test bed has been designed that enables simultaneous calcium fluorescence optical imaging and MR acquisition. A manuscript describing this work is submitted to NMR in Biomedicine in August of 2014.
