In a subsequent probe trial, the platform is removed and the animals’ memory is evaluated by their swimming persistence in the surroundings of the previous platform location 6. A typical experimental protocol consists of a set of trials, divided over a few days, during which the starting position of the animals is changed but the platform is kept at the same location. For experiments with rats typical maze dimensions are a tank with a diameter of 1 to 2 meters, in which a 10–15 cm platform is placed 4, 5. The MWM pool sizes vary greatly between experiments and depend on the types of animals used. Because the platform is hidden, animals cannot memorise its location directly and have to rely on external contextual visual cues for orientation. In this task, rodents are placed in a circular water pool with the goal of finding a submerged escape platform, which is made invisible by using, for instance, milky water or completely black walls in the experimental setup. The Morris Water Maze (MWM) 1, 2 navigation task is widely used in spatial learning studies 3. Our method allows us to reveal significant and systematic differences in the exploration strategies of two animal groups (stressed, non-stressed), that would be unobserved by earlier methods.
To this end, we take a different approach: we look for segments of diverse animal behaviour within one trial and employ a semi-automated classification method for identifying the various strategies exhibited by the animals within a trial.
However, these approaches typically consider trajectories as a whole and as a consequence they assign one full trajectory to one class, whereas animals often switch between these strategies and their corresponding classes, within a single trial. Other methods focus on classifying trajectory patterns to stereotypical classes representing different animal strategies. Classical performance measures of animals in the Morris Water Maze include the escape latency and the cumulative distance to the platform. The Morris Water Maze is a widely used task in studies of spatial learning with rodents.