Brain rhythms and dynamic states: control by cortical inhibitory networks

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Information processing in the brain is performed through interactions between many cells which form functional networks of excitatory and inhibitory neurons (or excitable brain cells) that produce rhythmic outputs.  The existence of these population oscillations which can be correlated with specific behavioural states depends on the particular properties of the participating cells and their connections.  How many cells and what properties are critical, are fundamental questions that we need to address if we are to understand the genesis and control of brain rhythms.  Furthermore, the contribution of diverse populations of inhibitory cells is known to be essential in the production of many brain rhythms. The hippocampal formation is a relatively simple cerebral cortical brain structure that is known to be important in learning and memory.  In this proposal, we use the availability of an in vitro hippocampal preparation which produces population oscillations without pharamacological manipulation (hence its relevance to the whole animal) to understand brain oscillations.  These oscillations mimic behaviourally relevant oscillations in terms of their frequency and pharmacological responses.  They are also known to be critically dependent on inhibitory cell characteristics.  We will use a newly developed method which allows the many inputs to brain cells to be statistically characterized from intracellular recordings.  Together with previous theoretical insights of excitatory and inhibitory network models, we will develop biologically-based models and perform simulations that will directly link the experimental data with the modelling studies and theoretical insights.  In this way, we will be able to probe the nonlinear complexities of brain dynamics and develop an understanding of how brain rhythms arise.