CTN: Soledad Gonzalo Cogno

Soledad Gonzalo Cogno

Seminar Time: 11:30am

Date: Wed 3/19/25

Location: JLG, L5-084

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

Note: Everything I will present in this talk is preliminary – Feedback and ideas will be very much appreciated!

Abstract: The medial entorhinal cortex 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 entorhinal cells can organize their activity into ultraslow oscillations (frequency < 0.1 Hz) that manifest as periodic sequences of activity in the neural population (Gonzalo Cogno et al., 2024). These ultraslow periodic sequences were recorded while mice ran at free pace on a rotating wheel in darkness, with no change in running direction and no scheduled rewards. 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. In this presentation I will show that in free foraging conditions, MEC neuronal activity can organize into sequences. However, the sequential activity is now characterized by resettings and interruptions. By developing a computational model, we investigate the conditions under which the sequences reset. In addition, we found that during slow-wave-sleep neural activity is also organized into ultraslow oscillations, but not into sequences. The oscillations also manifest in the hippocampus, and are highly synchronized with those in the MEC. These results suggest the presence of internal dynamics that unfold at ultraslow time scales, and that are modulated by sensory information and cognitive demands.

Because oscillations and sequences are not the only way into which neural activity can organize at ultraslow time scales, we next sought to determine whether other slowly changing patterns of activity are present in the MEC. If those exists, it is yet an open question whether, and how, those are transformed in the hippocampal-entorhinal circuit. We found that when animals ran at free pace on a rotating wheel in darkness, the activity in the MEC, lateral entorhinal cortex (LEC) and hippocampus slowly drifted over session time, enabling a readout of episodic time. However, the drift in the MEC and the hippocampus, but not in the LEC, significantly decreased when animals ran in an open field arena. These results suggest that the slow drift of hippocampal and MEC activity is attenuated by spatial landmarks when these are present.

All in all, our results point to the existent of ultraslow dynamics in the entorhinal-hippocampal circuit that may facilitate the encoding of experience at behavioral time scales.