The hippocampal theta oscillation may be generated by chimera dynamics

The 8-12 Hz theta rhythm observed in hippocampal local field potentials of animals can be regarded as a "clock" that regulates the timing of spikes. While different interneuron sub-types synchronously phase lock to different phases for every theta cycle, the phase of pyramidal neurons spikes asynchronously vary in each theta cycle, depending on the animals position. On the other hand, pyramidal neurons tend to fire slightly faster than the theta oscillation in what is termed hippocampal phase precession. Chimera states are specific solutions to dynamical systems where synchrony and asynchrony coexist, similar to the hippocampal theta oscillation. Here, we test the hypothesis that the hippocampal theta oscillation emerges from chimera dynamics with computational modelling. We utilized multiple network topologies and sizes of Kuramoto oscillator networks that are known to collectively display chimera dynamics. We found that by changing the oscillators intrinsic frequency, the frequency ratio between the synchronized and unsynchronized oscillators can match the frequency ratio between the hippocampal theta oscillation ({approx}8 Hz) and phase precessing pyramidal neurons ({approx}9 Hz). The faster firing population of oscillators also displays theta-sequence-like behaviour and phase precession. Finally, we trained networks of spiking integrate-and-fire neurons to output a chimera state by using the Kuramoto-chimera system as a dynamical supervisor. We found that the firing times of subsets of individual neurons display phase precession. These results imply that the hippocampal theta oscillation may be a chimera state, further suggesting the importance of chimera states in neuroscience.