Two-photon calcium imaging of memory engrams throughout the hippocampal formation in behaving mice -

Institute of Physiology University of Freiburg

In the seminar room, 11 am

Abstract: Every day, we form memories about episodes of experiences that we make. The hippocampus is the cardinal brain structure for the formation of such episodic memories and cellular ensembles in this brain structure form representations or ‘engrams’ of each individual memory. To observe the formation and maintenance of such memory engrams, we repeatedly monitor the activity of thousands of hippocampal neurons using two-photon calcium imaging in head fixed mice. During our measurements, the mice perform memory tasks in a virtual environment, allowing us to monitor neuronal engram activity during encoding and recall of memories related to the virtual sceneries. Intriguingly, the coding properties of individual neurons differ vastly across the hippocampal formation. Pyramidal cells in the CA1 and CA3 areas show precise spatial tuning and remap rapidly between behavioural contexts, while granule cells of the dentate gyrus show a generalizing code. Furthermore, the firing fields of pyramidal cells are time-sensitive and remap as days pass, while those of granule cells are stable over many days. Our results suggest a multi-step process of memory assembly within the hippocampus with specific features being represented by the individual hippocampal subfields.

Invited by the students and postdocs of Inmed

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