Scientific lectures: Ultraslow patterns of neural population activity in the entorhinal-hippocampal circuit

The medial entorhinal cortex (MEC) hosts many of the brain’s circuit elements for spatial navigation and episodic memory, operations that require neural activity to be organized across long durations of experience. We have previously found that when mice were head-fixed on a wheel and ran at their own pace in darkness, entorhinal cells organized their activity into ultraslow oscillations (frequency < 0.1 Hz) that manifested as periodic sequences of activity in the neural population (Gonzalo Cogno et al., 2024). It remains unknown, however, whether the sequences also occur during more naturalistic behaviours, for example while mice run in an open field arena, or during sleep. We found that in free foraging conditions, MEC neuronal activity can organize into sequences. Within a session, the MEC always generates the same sequence ordering, and this ordering recurs over time. However, the sequential activity is now characterized by resettings and interruptions. By developing a computational model, we characterize the repertoire of network architectures that can generate the experimentally observed sequences, and investigate the conditions under which the sequences reset. In addition, we found that that ultraslow periodic activity persisted during sleep, particularly during slow wave sleep. However, this ultraslow activity manifested as ultraslow oscillations that were highly synchronous across the population, and not as sequences. These oscillations also manifest in the hippocampus. Our results suggest the presence of internal dynamics that unfold at ultraslow time scales, and that are modulated by sensory information and cognitive tasks.

Hosted by Jacobo SITT

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