Links between the hippocampal theta oscillation and chimera dynamics

Maria Masoliver

The 8-12 Hz theta rhythm in the hippocampus can be regarded as a “clock” since it regulates the timing activity of hippocampal neurons. While interneurons tend to fire at the same phase for every theta cycle, the firing of pyramidal neurons varies in each theta cycle, depending on the animal’s position. The pyramidal neurons tend to fire slightly faster than the theta oscillation in what is called hippocampal phase precession. Here, we show that hippocampal theta oscillations and phase precession-related firing patterns may emerge from a chimera state where synchrony and asynchrony coexist. We utilize a network of Kuramoto oscillators with uniform intrinsic frequencies that readily display a collective chimera state. By changing the oscillators’ intrinsic frequency, we can tune the frequency ratio between the synchronized and unsynchronized oscillators to reach the frequency ratio between interneurons and pyramidal neurons in the hippocampus. The unsynchronized oscillators vary systematically within the synchronized population, as seen in the pyramidal neurons undergoing phase precession. Additionally, we show how we can train a spiking network of integrate-and-fire neurons to output a chimera state. Analyzing the firing times of the individual neurons we observe how phase precession and spike sequences occur for subsets of neurons. These results imply that the hippocampal theta oscillation may be a chimera state, further suggesting the importance of chimera states in neuroscience.

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