For nearly two decades the Morris Water Maze (MWM) is a task extensively used and accepted by behavioral physiologist and pharmacologist to assess and compare learning and memory in rodents. While simple at first glance, the MWM employs a variety of sophisticated mnemonic processes.

These processes encompass the acquisition and spatial localization of relevant visual cues which are subsequently processed, consolidated, retained, and then retrieved, in order to successfully navigate and thereby locate a hidden platform to escape the water.

The MWM procedure offers a number of advantages as a means of assessing cognitive function in rodents:

• It requires no pre-training period and can be accomplished in a short period of time with a relatively large number of animals.
• (Through the use of training as well as probe or transfer trials, both learning and retrieval processes can be analyzed.
• Through the use of video tracking devices and the measuring of swim speeds, non-mnemonic behaviors or strategies can be delineated, and motor or motivational deficiencies can be identified.
• Visible platform tests can identify gross visual deficiencies that might confound interpretation of results obtained from standard (MWM) testing.
• By changing the platform location, both learning and re-learning experiments can be accomplished. 

Primarily designed to measure spatial learning and recall, the MWM procedure has now become quite useful for evaluating the effects of ageing, experimental lesions, and drug effects, especially in rodents. Several lines of evidence also confirm the usefulness of the model for research relevant to the study of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, which feature cognitive decline. 

Different king of protocols can be used for evaluation of non-spatial memory processes (cued version). Here the more common experimental phases used in this test:

The Visible Platform Test

The visible platform version of the Morris water maze test was used to assess nonspatial learning and to rule out the possibility that the spatial learning deficits detected might actually be a product of deficient escape motivation or impairment of vision and/or motor skills. The platform location is indicated by a marker rising above the water, as an example, by attaching of a high-contrast striped flag, and normal animals use the visual cues to escape from the water. This simple associative nonspatial task is believed to be independent of hippocampal function.

The Hidden Platform Test

Place navigation requires the mice to learn to swim from any starting position to the escape platform, thereby acquiring a long-term memory of the platform’s spatial location.

The platform is rendered invisible by rendering the water opaque. Animals are tested individually and placed into various quadrants of the pool and the time elapsed and/or the distance traversed to reach the hidden platform is recorded. Various objects or geometric images (e.g. circle triangles, squares), are often placed in the testing room or hung on the wall so that the animals can use these visual cues as a means of navigating in the Maze. 

With each subsequent entry into the Maze, the animals progressively become more efficient at locating the platform, thus escaping the water by learning the location of the platform relative to the distal visual cues. 

The Transfer Test (Probe Test)

The probe trial provides an index of the animal’s tendency to persist around the platform’s previous location and is generally considered to be a measure of retention.

After completion of the Hidden Platform test; next; trials are given in which the platform is removed from the pool to measure spatial bias. This is accomplished by measuring the time and distance traveled in each of the four quadrants. The important measure will be the percentage of the total time elapsed and distance swam in the zone of the previous target quadrant.

The Relearning Test or repeated acquisition task

This test measures the ability of the animals to find a new platform location using the procedural knowledge and spatial cues already learned in the reference memory version of the task (Hidden Platform Test).

After completion of the Hidden Platform Test, the probe Test and a rest period, a second series of trials may be conducted as described in the Hidden Platform Test, except that the location of the platform is changed each day to a different quadrant. The animal must find it across several trials.