Functional populations in the pyramidal cell layer of hippocampal area CA1

The hippocampus is an area of the brain that plays a crucial role in spatial navigation. Place cells are hippocampal pyramidal cells which hold a representation of self-location by firing selective in a single location: the place field. Pyramidal cells in CA1, including place cells, respond differently to a variety of external factors, such as cues or rewards in the environment, and internal factors, such a brain state. As such, heterogenous functional populations are present in CA1 both in addition to, as well as within the place cell population. I studied how pyramidal cells in CA1 form different functional populations in response to the manipulation of internal and external factors. A combination of modelling approaches and mouse experiments was used to investigate this. Models of place cell populations were created to test the performance of place cell detection methods. Mice with a genetically encoded calcium indicator were trained to perform an object location novelty experiment in a virtual reality environment while their hippocampus was imaged using two-photon microscopy. Our modelled place cells revealed one specific method to be optimal for detecting place cells. Using this method, I found that object location novelty had a stronger effect on place cell coding than cue abundance of an environment. In addition to the place cell populations, I identified two novel functional populations, the Stationary Low-frequency Oscillatory (SLO) and Odd Running-active Low-frequency Aperiodic (ORLA) cells, within CA1 that are characterized by periodic and aperiodic activity respectively. These results first contribute to an increased consensus on place cell detection, and by extension place cell identity, used within the field. I also show the impact of both external factors, in the place cell population, and internal factors, in the SLO and ORLA cells, giving us an increased understanding of factors that differentially drive hippocampal activity.