Abstract
In mammals, the hippocampus is responsible for the formation of spatial and episodic memories, the proper generation and recall of which are crucial to an animal’s survival. Specifically, pyramidal neurons in layer CA1 of the mouse hippocampus are recruited as place cells. These cells form place fields, which demonstrate peak activity as the mouse dwells within specific locations of the environment. As place cells are recruited to form a general map of the environment, these cells become sensitive to salient locations, such as a food source. Mapping place fields will show an overrepresentation of such locations, as multiple place cells are recruited to form fields at that location. As critical as the formation of a rigid spatial map is to properly recall prior events and environmental features, proper hippocampal function must also ensure that these spatial memories are flexible enough to update in response to changes in the environment. This thesis will investigate what effect cue salience has on the rate of remapping in place cells, as well as activity changes related to this remapping. I hypothesize that more salient changes to an animal’s environment will result in larger changes in calcium activity, and a higher rate of place field reformation. To test this hypothesis, I analyzed two-photon calcium imaging data recorded by Dr. Christine Grienberger from CA1 pyramidal neurons of head-fixed, behaving mice as they ran on a cued linear track. I created a custom model to label regions of interest (ROIs) in the structural registration tool Cellpose, and ran these ROIs through a second, activity-based registration tool, Suite2p. I then used a MATLAB pipeline to identify place cells. Expanding upon this single cell data, I observed changes in cellular activity, for example a change in the location of peak calcium activity to overrepresent the new reward location, the rate of place cell recruitment in response to environmental manipulation, and an increase in the rate of place cell recruitment after either the introduction of a light cue or the change in location of the sucrose reward provided at each lap. I also investigated, but saw no changes in, velocity and lick rate during the session. This was to determine if I could observe potential behavioral changes in response to the experimental manipulations and resulting changes to calcium activity. Together, I sought to use these observations to determine adaptations in the spatial map to environmental changes and whether changes in calcium activity resulted in behavioral adaptations.