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Morris Water Maze
The Morris water navigation task is a behavioral procedure widely used in behavioral neuroscience to study spatial learning and memory. It was developed by neuroscientist Richard G. Morris in 1981, who used it to show that lesions of the hippocampus impaired spatial learning. Source: Wikipedia
** General settings
The paradigm consist in a pool between 1.20 and 1.80 m radius (1.50 in our case). The mice are placed inside the pool and should escape reaching a platform which can be placed in different parts of the pool. Visual cues, such as colored shapes, are placed around the pool in plain sight of the animal, thus, the mice can use them to orient itself and reach the platform. Each of the following sessions corresponds to a single day and are repeated 4 times (trials), spaced around 30 minutes (the time that the experimentalist need to make a trial to each animal and start again). In each trial the animal is put into the pool in a different quadrant (cardinal point) and then retrieved when it reaches the platform or if never does, after 60 seconds.
** Pre-training (1st Day 4 trials)
The platform is placed in the center of the pool slightly above the water level. The end of this phase is that the animal understand the procedure of the experiment, learns what it has to do.
{{{Note: When the animal reaches the platform but does not stay on it (it jumps again inside the water) we have what is called a procedural error, i.e. the animal has not understood the test, the reward of which is to be removed from the platform and placed in the cage again once the animal has reaches the platform.}}}
- Acquisition 1-5 (2nd to 6th day, 4 trials per day)
The platform is fixed in NE or NW during all the days and trials (nearest point to the experimenter to pick up the animal from the platform).
During acquisition phase the platform is just below the water, thus the animal can only know where it is by the cues present in the room walls.
Entering point is alternated within trials. During this sessions the animal will learn where the platform is and thus, it will improve the performance along time (figure 1).
Of course this acquisition has also a memory component but the key feature to be analyzed will be learning.
{{{Note: The are two easy entering points where the cues lead the animal to the platform directly.}}}
Figure 1 This figure shows the latency time, i.e. the time the animal needs to reach the platform (x axis) across the time course of the experiment, sessions (y axis). Black points correspond to wt animals and gray to mutants. It is observed that Wt animals perform better the experiment as well as the improvement of animals during acquisition sessions.
** Removal (7th day, 1 trial)
As its name suggests during this session the platform is removed from the pool. What we want to assess is the memory, if the animal remembers where the pool was placed it will spent more time in this zone (see figure 2).
{{{Note: This session has only a trial due to the fact that animals learn that the platform is not present and thus more trials won't give any further information.}}}
Figure 2 This graph shows the time the animal has been in each part of the pool. The color scale goes from red to black and indicates the time the animal has been in each zone, being red the bigger amount of time and black not visiting the zone at all. Specifically this plot corresponds to the removal session and it could be seen that animals spend much part of the time in the zone where the platform previously was.
** Cued (8th day, 4 trials)
All cues in the walls are removed and only a cue is placed on the platform, in our case the Jolly Roger flag. This session serves to measure the motivation of the animal and of course the visual capacity. The animal is put into water each time from a different cardinal point.
- Reversal 1-2 (9th to 10th day)
The platform is just placed in the opposite point from where it was placed during the acquisition phase. Reversal phase is used to evaluate which is the flexibility of the animal.
{{{Note: During all preceding sessions the main structure involved in the behavior of the animals is the hippocampus while during reversal phase are the cortical areas.}}}
Animals are record during all the sessions using SMART software. The information is stored in binary files, trs files, and can be read and processed using the SMART application. A plain text file can be created by SMART. This file summarizes the position of the animal each two tenths of second. Plain text files are the input for JTracks a JAVA application which processes the data in order to smooth paths and make figures of time spent by the animal in zones (figure 2) or the path followed by the animal during the trial duration (figure 3).
Figure 3 Animal paths followed during the cued session by a wt animal and a transgenic. While wt animal does not travel a big distance, "it knows where the platform was", transgenic keeps looking forward for it.
Vorhees, C. V., & Williams, M. T. (2006). Morris water maze: procedures for assessing spatial and related forms of learning and memory. Nature protocols, 1(2), 848-58. Nature Publishing Group. doi:10.1038/nprot.2006.116
Graziano, A., Petrosini, L., & Bartoletti, A. (2003). Automatic recognition of explorative strategies in the Morris water maze. Journal of neuroscience methods, 130(1), 33-44.