Exploring Environmental Factors Favoring the Emergence of Off-Track Scanning Behavior in Rats

The hippocampus is essential to episodic memory and the ability to create cognitive representations of space. Place cells in the rodent hippocampus are thought to provide the neural substrate of these cognitive maps. However, most studies of place cells have relied on highly stereotyped, over-trained "random" foraging behavior. Relatively little is known about how spontaneous exploratory behaviors contribute to the formation and stability of the place cell map. One exception is "head-scanning," lateral head movements performed by rodents when exploring an environment. When animals scan off a circular track, place cells may abruptly form or potentiate an adjacent on-track firing location that persists on subsequent laps, potentially contributing to the remapping of the place cell code. No systematic investigation of this phenomenon has employed linear tracks. It has been suggested that ballistic trajectories on a linear track might reduce the natural occurrence of scanning. Further, reward location could confound scanning-induced remapping of firing locations. This thesis addressed these questions and explored the environmental and experimental task conditions that may influence the emergence of scanning on a long (250cm) linear track. We show that rats reliably scan throughout the length of a long linear track, irrespective of the spatial distribution of reward. Moreover, scanning behavior is driven by novelty conditions, especially room changes. Our data lay the foundation for the investigation of non-local effects of scanning behavior on the place cell code and contribute to the standardizations necessary for future studies.