The Prominence of Action Sequences and Behavioral Similarity in the Morris Water Task

The question of What is learned when navigating to a place is reinforced has been the subject of considerable debate. Prevailing views emphasize cognitive structures (e.g., maps) or associative learning, which has shaped measurement in spatial navigation tasks (e.g., the Morris water task [MWT]) toward selection of coarse measures that do not capture precise behaviors of individual animals. We analyzed the navigation paths of 15 rats (60 trials each) in the MWT at high temporal resolution (30Hz) and utilized dynamic time warping to quantify the similarity of paths within and between animals. Paths were largely direct, yet suboptimal, and included changes in speed and trajectory that were established early in training and unique to each animal. Individual rats executed similar paths from the same release point from trial to trial, which were distinct from paths executed by other rats as well as paths performed by the same rat from other release points. These observations suggest that rats learn to execute similar path sequences from trial to trial for each release point in the MWT. Occasional spontaneous deviations from the established, unique behavioral sequence, resulted in profound disruption in navigation accuracy. We discuss the potential implications of sequence navigation behaviors for understanding relations between behavior and spatial neural signals such as place cells, grid cells, and head direction cells.