Modeling spatial learning in rats based on Morris water maze experiments.

The Morris water maze, developed by Morris (J Neurosci Methods 1984: 11: 47-60), is a behavioral experiment designed to test the spatial memory. When repeating the experiment several times, the changes in time (latency) and distance (path) taken to reach the platform are indicators for the learning and memory abilities of the rat. In juvenile toxicity studies, it is of interest to test whether dosing juvenile rats with some compound of interest has an effect on its learning ability. The traditional analysis uses non-parametric tests to check for a possible dose-effect. However, due to the many tests performed, this approach lacks power. Here, an alternative method is proposed, accounting for the longitudinal design of the study, the right-censoring of observations when animals did not find the platform and the correlation between the time and distance taken to reach the platform.