Morris water maze

The morris water maze (MWM) is one of the most common tasks for the assessment of spatial memory. Animals use spatial cues (most often visual cues) in order to help locate a platform hidden in opaque water in which they must otherwise continuously swim. Several variables determine whether or not habituation to the MWM apparatus is appropriate prior to experimentation. First, depending on the duration of the test, many animals (especially rats) will not actively seek escape but will rather explore the swimming arena continuously. This is more common in short-duration experiments, for example, those lasting less than one minute. In this case, pre-experiment exposure to the arena with the platform exposed (i.e. un-dyed water in order to reveal the platform location) will indicate the presence of the platform, thereby ensuring that the animal understands the breadth of the task.

Additionally, a pre-experimentation acquisition exposure to the MWM arena performed in the absence of spatial cues (such as objects or wall-markings within the room which are visible from within the MWM) eliminates the confounding variable of environmental novelty in measurements such as distance moved and time spent per quadrant in the acquisition phase of the test.

Conversely, the absence of a platform may induce significant stress in animals seeking an escape and thus confounds any measures of learning acquisition with increased levels of stress and anxiety as a result of the no-platform habituation procedure. Similarly, exposure to the arena in a no-platform condition followed by a test in which the platform is present has been argued to be a form of reversal learning, rather than spatial acquisition, and thus significantly changes the interpretation of outcome results.[6]

Thus, while apparatus habituation is not commonly used for tests involving environmental novelty, exposure to the MWM in controlled conditions may be useful for achieving uniform behavioral results in certain circumstances. Researchers using short protocols (i.e. less than one minute) may pre-expose their animals to the MWM in un-dyed water in order to indicate the presence of an escape platform. Importantly, this habituation test should be done in the same environment (i.e. testing room) in which the experiment will take place, however, any spatial cues such as wall markings which are visible from within the MWM should be removed for the duration of the test. This habituation session should be performed on the day prior to the experiment.