Functionalities Emerging in Adaptive Brain Networks through Selective Synchronization of Neurons by Targeted Feedback

Overview The proposed project is motivated by two general aspects of the brain: its complex connectivity, including extensive feed-back connections through which information processing in one brain area can be modified by the brain area that receives that information, and the wide-spread occurrence of rhythms that indicate enhanced coherence in the spiking of neurons in a population. The over-arching goal of the project is • to provide insight into the functionalities that can arise from feed-back that takes into account prior experience stored in memory and that modifies the coherence of activity in specific target subnetworks, • to elucidate properties of the participating neurons and connections that enable these functionalities. The PI will investigate these questions in the context of the olfactory system, which is very well suited for such a study. The olfactory bulb, which performs the initial processing of olfactory information, exhibits strong θ-, β-, and γ-rhythms and receives extensive feed-back connections from cortex to the population of granule cells that are central in generating the γ-rhythm. Moreover, anatomically this feed-back connectivity is highly plastic since the granule cell population undergoes persistent turn-over. This may allow the system to form feed-back connections through which a given cortical cell can target very specific granule cells. The PI will develop a biophysically motivated computational model for the evolution of the bulbar-cortical network connectivity that takes into account the control that cortex exerts on this process. He will investigate the structured networks that emerge from this process when the system is trained with a set of stimuli. The neurons will be described with conductance-based models that capture several important observations of the neuronal dynamics in the olfactory bulb. Central to the proposed project will be an analysis of the extent to which the cortical network can control the coherent activity within specific subnetworks, which result from the exposure to specific stimuli. The PI will employ computational methods to investigate the full system. To gain insight into specific mechanisms that are relevant in the full system the PI will extract simpler, more general models, which are amenable to exact or asymptotic analytical methods including weak coupling and bifurcation theory for delay equations. Intellectual Merit The proposed work will further the understanding of various aspects of network evolution and of coherent spiking and it will identify and analyze possible functionalities arising from specific feed-back control of coherence: • It will identify elements of the structural plasticity that aid in establishing precise feed-back control of specific neuronal populations. • It will provide insight into the synchronization of neurons exhibiting subthreshold oscillations, identifying the role of various biophysical properties of the neurons and their synaptic coupling. • It will elucidate the role of delays in the formation and competition of rhythms in interacting networks. In the olfactory context this will address the experimentally observed transition from γ- to β-rhythms. • Proposed and analyzed functionalities in the context of the olfactory system include i) the binding of different olfactory stimuli into a single odor object by cortically controlled synchronization of rhythms in different subnetworks, each corresponding to an individual stimulus. ii) the transfer of cortical function to the olfactory bulb by cortically control