Generation and propagation of transient neuronal assemblies in the mouse hippocampus

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Within the general topic of propagating neuronal assemblies, we will focus on a specific model system, namely hipocampal sharp wave-ripple complexes. These patterns of network activity involve defined sub-sets of principal neurons while propagating through the hippocampal formation. They might play a role in declarative or spatial memory consolidation, indicating that participating cells are selected by previous processes of plasticity. It can also be inferred that several clearly distinct assemblies co-exist in the hippocampus. We want to use modern electrophysiological and optogenetic techniques to monitor propagating assemblies in mouse hippocampal-entorhinal slices. We then want to apply modern algorithms of analysis, asking the following questions: i) How many assemblies can be identified in the hippocampus? ii) Are downstream assemblies completely determined by preceding patterns of activity in upstream assemblies? iii) Can we induce new assemblies by repetitive activation of defined subsets of neurons? iv) Are defined assemblies unambiguously reflected in distinct field potential waveforms?Together, our work shall shed light on the stability and plasticity of propagating assemblies. We will refine our methods, not at least by exchanging techniques of recording and analysis with other members of the consortium. Finally, our combined analysis of field potentials and single-neuron activity will help to develop new approaches for high-resolution EEG analysis.