What Is the Morris Water Maze?
The Morris Water Maze was introduced by Richard G.M. Morris in 1981 as a test of spatial learning and memory. The apparatus consists of a large circular pool (typically 120-180 cm diameter) filled with opaque water (made milky with non-toxic paint or powdered milk) maintained at 22-26 degrees C. A hidden escape platform is submerged 1-2 cm below the water surface in one quadrant of the pool. The animal is placed in the water at varying start locations around the perimeter and must use distal visual cues (posters, shapes, or landmarks on the walls of the testing room) to navigate to the hidden platform. Over multiple training trials across several days, healthy rodents learn the spatial location of the platform, showing progressively shorter escape latencies and more direct swim paths. The MWM has become the gold standard for assessing hippocampal function, spatial reference memory, and the effects of pharmacological, genetic, and lesion manipulations on spatial cognition. Its power lies in the fact that it requires allocentric spatial navigation — the animal must build a cognitive map from distal cues rather than relying on proximal or intramaze cues.