Emergence of memory engrams in the rodent hippocampus

• Applicant: Professorin Dr. Marlene Bartos
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Human Cognitive and Systems Neuroscience
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410026292

The hippocampus is decisive for the storage of conscious memories. Memory-specific neuronal ensembles – so called engrams – exist in all subfields of the rodent hippocampus. However, knowledge about how these engrams develop and maintain memory-specific activity during long-term learning is scarce. In the here proposed project, we aim to use chronic two-photon calcium imaging of population activity in the hippocampus of head-fixed mice performing a goal-oriented spatial memory tasks in a virtual reality and record principal cell activity in the major hippocampal subfields, the dentate gyrus, CA1 and CA3. A subpopulation of hippocampal principal cells have place cell characteristics and discharge once the mouse explores a specific spatial field. It remains, however, unclear how place cell assemblies as a whole representing spatial contexts emerge in the three hippocampal subfields during learning. To address this question we recently established a behavioural paradigm in which head-fixed mice explore a ‘familiar’ virtual environment in which they have been trained over several days to obtain food rewards at specific locations. After training in the familiar context, mice are exposed to a ‘novel’ virtual environment to explore new reward locations. In the proposed project, we will first, examine how place cell assemblies emerge during the learning process in the ‘novel’ context on subsequent days and how they differ from cell associations representing the familiar context. Second, we aim to test whether reliability in the representation of the learned novel spatial environment as well as the differentiation between both contexts differs among the three hippocampal areas. Finally, we aim to examine the influence of inputs from the medial entorhinal cortex transmitting contextual information, on the characteristics of hippocampal cell assemblies representing a spatial environment. Thus, within this proposed project we aim to obtain a better understanding in the representation of memories along the classic hippocampal tri-synaptic loop based on the code provided by the dentate gyrus.

• DFG Programme: Research Grants