2-Photon population imaging of the denatate gyrus – from microcircuit function to control of behaviour

The dentate gyrus (DG) is the entrance gate of the hippocampus and translates the rich input stream from the entorhinal cortex into sparse non-overlapping memories. The network mechanisms underlying sparse coding are however largely unknown. To study the emergence and activity of hippocampal memory engrams in awake, behaving animals, we use two-photon calcium imaging in the dentate gyrus and the hippocampal subfields CA1-3 of head-fixed mice. During the imaging sessions, the mice perform a contextual discrimination task in a virtual environment displayed on screens around them (Hainmueller and Bartos, 2018). We investigate, how principal neurons in different hippocampal subfields represent the space of the virtual sceneries and how these representations develop with increasing familiarity of the environment to the animal. We further study the local microcircuit mechanisms underlying the establishment of memory-bearing neuronal ensembles (Sheffield and Dombeck, 2017). Currently, we investigate how the activity of local inhibitory circuits is modulated by sensory experience as well as behavioral novelty detection. By these means, we are trying to decipher how neuronal circuits in the hippocampal formation store and retrieve the contents of complex episodic memories.