Theta and respiration: Interactions of two different rhythms in the entrainment of neuronal activity

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The mammalian brain expresses different types of network oscillations which entrain neurons into a common temporal regime. The resulting spatio-temporal activity patterns are believed to underlie neuronal representations of perceptions, actions, memories or other cognitive acts. There are multiple different types of oscillations which vary in frequency, underlying mechanisms, spatial extension and correlation with different functional states. In many cases, several rhythms co-exist in the same local network, sometimes forming nested fast and slow oscillations. It is far from clear how individual neurons are affected by such complex patterns.We want to study a recently discovered interaction between two different oscillations which cover strongly overlapping frequency bands in the mouse brain: theta oscillations (4-12 Hz) and respiration-related rhythms (RR, 2-12 Hz). During past years, we and others have shown that respiration-related network oscillations entrain neurons in multiple brain regions, far beyond specific respiratory or olfactory networks. In many of these areas, e.g. the parietal and frontal cortex or the hippocampus, we observe theta- and RR-oscillations at the same time. This finding points towards an interaction between autonomously generated rhythms (theta) and sensory feedback (RR). We want to analyze this interesting model system for interactions between different oscillatory regimes, asking three fundamental questions:1. How do co-existing theta and RR affect multi-neuronal activity patterns?2. What are the mechanisms of neuronal entrainment, and do these differ between both rhythms?3. (How) do non-synaptic (`far field´) mechanisms affect multi-neuronal patterns in cortical networks?We will apply multiple electrophysiological methods in vivo and in vitro, including tetrode recordings, multi-electrode arrays, high-resolution juxta-and intracellular techniques and advanced methods of analysis. Stimulation of neuronal activity includes optogenetic approaches in vivo and external AC-potentials in brain slices in vitro. Together, our experiments shall elucidate new mechanisms underlying the generation of complex neuronal activity patterns. At the same time, we want to shed light on the impact of sensory (respiratory/olfactory) feedback on widespread activity patterns in the murine brain.