Department of Psychology, Michigan State University (MSU)
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Nunez, J. Morris Water Maze Experiment. J. Vis. Exp. (19), e897, doi:10.3791/897 (2008).
The Morris water maze is widely used to study spatial memory and learning. Animals are placed in a pool of water that is colored opaque with powdered non-fat milk or non-toxic tempera paint, where they must swim to a hidden escape platform. Because they are in opaque water, the animals cannot see the platform, and cannot rely on scent to find the escape route. Instead, they must rely on external/extra-maze cues. As the animals become more familiar with the task, they are able to find the platform more quickly. Developed by Richard G. Morris in 1984, this paradigm has become one of the "gold standards" of behavioral neuroscience.
Setting up the water maze
Pre-training for the water maze
Water maze testing
The water maze task was development by Morris 5. This task can be altered in numerous ways to investigate working memory, reference memory and task strategy 6. The procedure described here contains two critical variables which represent a deviation from other versions of the water maze: pretraining, and testing on a single day.
Pretraining - the hippocampus is involved in spatial/relational memory 7-8. The water maze specifically tests spatial memory 3. However, there are numerous other components of the task that do not involve spatial memory: the stress involved with the task, the understanding of the rules of the task (that to "escape", the animal must find a hidden platform, and stay on it in order to be "rescued"), and the understanding that there is a means of escaping the task 9. Learned helplessness also involves a tank of water, but the rules (there is no means of escape) are quite different 10. The three pretraining trials "teach" the animals about these properties of the task. They learn that they will be placed into a pool of tepid water and swim around for a minute, but be removed after. They are taught to find the platform (because it is visible) and that staying on it will lead to their "escape" from the maze. And they are taught that the task has an end. Therefore, this hippocampal-independent learning does not confound the analysis of the water maze testing data.
Testing on a single day - Most often, water maze testing occurs across two to four days 3. In this way, acquisition and retention can be assessed. However, in some populations, this is not a viable option. Such is the case when investigating female mammals. Female rodents, humans, primates, etc, all have cyclic changes in steroid hormone levels 11-12. These hormones have profound effects on hippocampal-dependent task performance, hippocampal anatomy and hippocampal cell function 13-14. Testing across multiple days would be akin to testing a single animal across numerous conditions low estradiol and progesterone, elevated estradiol and progesterone, and intermediate estradiol and progesterone. To eliminate this confound, testing occurs across a single day.
The authors have nothing to disclose.
JLN was supported by MH 68347.
|SMART System||San Diego Instruments||This system is not a requirement €“ there are many other behavioral systems on the market.|
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