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CUED AND HIDDEN VERSIONS OF 

MORRIS SWIM MAZE TASK

Apparatus: The water maze consists of a round galvanized metal pool (100 cm inner diameter, 20.5 cm deep) filled with water to a depth of 17.5 cm. The water is kept at room temperature (24+/-1o C) and made opaque by adding a small quantity of nontoxic water-soluble paint. The escape platform is made of an 11.4 cm outer diameter clear acrylic tube resting on a 23.5 cm square clear acrylic base and is capped with a clear acrylic top. The top surface of the platform rests 1.5 cm below the surface of the water and 15 cm from the wall of the pool, and is scored with a checkered pattern for traction. The water maze is located in the center of a room with the four walls decorated to provide salient distal spatial cues (e.g., broad black vertical stripes, broad black horizontal stripes, a large black "X" on a white sheet, and a poster of a mouse). Computerized tracking system from San Diego Instruments

Procedure:

Cued condition (three day test)
1. Screw a long threaded rod into the submerged acrylic base which protrudes approximately 20 cm out of the water and on top of which is placed a red tennis ball.
2. Pseudo-randomly place the modified platform into each of the 4 quadrants (N, S, E, and W) for each block of 4 trials (never the same quadrant consecutively).
3. In addition, two different platform locations should be used in each quadrant.  One location should be closer to the wall and one is closer to the center of the quadrant compared to the platform location used during place training.  Locations should be pseudorandomly varied across trials.
4. A curtain should be suspended immediately around the pool to prevent learning distal cues.
5. Place the mouse, nose against wall, into the water at the appropriate release point.
6. Release points (NE, SE, SW, and NW) should be pseudorandomly assigned for each trial so that for each block of 4 trials, the mouse will be released once from every point, and will never be released from the same point consecutively.
7. Videotape every trial with an overhead camera, and record the paths of the mice with computerized tracking system.
8. Record the latency and distance traveled to reach the platform for each trial (escape latency, EL; path distance, DIST).
9. A trial ends when the mouse touches the platform with its front paws.
10. If the mouse does not find platform within 60 s, it will be manually placed on the platform and assigned a maximum score of 60 s
11. The mouse should remain on the platform for 5s and then be placed into a metal holding cage for 5s.
12. Move platform according to rules in step 2.
13. Place mouse back into water according to rules in steps 5-6.
14. Repeat steps 7-11.
15. Wait one hour.
16. Repeat steps 2-14 two more times (total of 4 trials per day)
17. Perform 4 trials per day on 3 consecutive days (12 trials total).
18. After each trial, total data to be collected for this condition should consist of 3 blocks (4 trials each) of EL and DIST.

Place condition (5 days total)
1. Prior to the start of the PLACE trials, the mouse should be placed on the platform in the pool for 30s, followed by 30s in a metal holding cage
2. For the PLACE condition, the rod should be removed from the base of the platform.
3. The location of the escape platform should be randomly assigned to 1 of 4 pool quadrants (N, E, S, or W), yet remain constant for each mouse throughout all testing trials.
4. The release points (NE, SE, SW, and NW) will be pseudorandomly assigned for each trial.
5. The mouse will be released once from every point, and will never be released from same point consecutively.
6. Begin each trial by placing the mouse, nose against wall, into the water at the appropriate release point.
7. A trial ends when the mouse touches the platform with its front paws.
8. Videotape every trial with an overhead camera, and record the paths of the mice with computerized tracking system.
9. On each PLACE trial record following data and analyze in 5 blocks of 4 trials each: EL, DIST, velocity (trial distance/latency to find platform)
10. If the mouse does not find platform within 60 s, it will be manually placed on the platform and assigned a maximum score of 60 s
11. The mouse should remain on the platform for 5s and then be placed into a metal holding cage for 5s.
12. Place mouse back into water according to rules in steps 4-6.
13. Repeat steps 6-11
14. Wait one hour.
15. Repeat steps 6-11 two more times (total of 4 trials per day)
16. Perform 4 trials per day on 5 consecutive days (20 trials total).
17. Probe trials:
18. Approximately 1 hr after the 4th trial on days 3 and 5, a probe trial should be given
19. Prior to the probe trials, the escape platform is removed from the pool
20. Release the animal across the pool from the previous location of the platform.
21. One hour later, perform another place trial as described in steps 6-11. (This trial is performed in order to avoid potential extinction effects and performance on this additional place trial is not be analyzed statistically)
22. On each probe trial, record following behavior: time spent searching the platform quadrant (probe time; PT), total distance traveled (DIST), number of crossings of the former platform location (CROSS), velocity, average proximity to platform location.

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