Time: 14:15-15:00

Place: D4-132

Title: Minute-scale periodic sequences of neural population activity in the cortex.

Host: Ass. Prof. Raffaela Cabriolu, Materials Theory Group, NTNU, Trondheim. 

Abstract: 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. While location is known to be encoded by spatially tuned cell types in this brain region, little is known about how the activity of entorhinal cells is tied together over time at behaviourally relevant time scales, in the second-to-minute regime. Here we show that MEC neuronal activity can be organized into ultraslow oscillations, with periods ranging from tens of seconds to minutes. During these oscillations, the activity is further organized into periodic sequences. The sequences involved nearly the entire cell population, and transcended epochs of immobility. Sequences manifested while mice ran at free pace on a rotating wheel in darkness, with no change in location or running direction and no scheduled rewards. It remains unknown, however, whether the sequences occur during other behaviours too, for example while mice run in an open field arena. Here we show that in free foraging conditions MEC neuronal activity can also organize into the periodic sequences. However, the sequential activity is now characterized by resettings and interruptions. By creating a computational model, we show that the sequences can reset in the presence of sensory stimulation eliciting the sudden activation of neuronal ensembles, as expected to happen during running in an open field arena and in the presence of strong landmarks. We further illustrate the potential role of the periodic sequences in facilitating, in downstream structures, patterns of neuronal activation that unfold at behavioural time scales.