K - Learning and Memory: Spatial

Objectives:

To learn about different types of spatial navigation, and the tasks that test them.
To gain experience with the Morris Water Maze and Exploration procedures.

Introduction:

Spatial learning is a complex behavior that has been quite amenable to behavioral neuroscience investigations. Much of the neural circuitry and molecular biology underlying spatial learning has been delineated. There are many approaches to studying spatial navigation, each of which uses different motivations and strategies. T, cross, and radial arm mazes use food rewards in hungry rats, while the Morris Water Maze uses an escape motivation. Finally, the exploration task capitalizes on rats’ natural curiosity (Save and Poucet, 2005). In this lab you will gain experience with two different spatial tasks, the water maze and the exploration task. The Morris Water Maze consists of a tank full of opaque water and a platform in the water to serve as an escape from the water. The water maze has a number of different permutations (Morris, 1981; Sutherland and Dyck, 1984). In “cue” learning there is a proximal cue that serves as a landmark for the platform, such as a visible platform or a flag attached to the platform or a cue on the wall inside the maze. In the “place” task the platform is hidden and the only cues are distally located outside the maze, on the walls of the room. In the “matching-to-place” task, the platform is moved to a new location each day, but stays in that spot all day. The rat learns that there is a solution, and that it must locate the platform, and that the platform will be there all day, but will be in a different spot tomorrow. (There is a great resource available on the internet at http://www.watermaze.org) In the exploration task, the animal is presented with a number of objects. After repeated exposure to the objects in the arena, the animal habituates to them (time spent examining the objects declines). When the animal is then exposed to the objects with one or two of them moved, it will increase its exploration in response to the spatial reorganization (Poucet et al., 1986). Small adjustments to the location of one object will yield more exploration of that object, while large relocations of a single object will increase exploration of all objects. There is likely an aspect of object recognition involved in this task as well (see Laboratory Exercise L).

Procedure:

Preparation: The water maze will need to be filled ahead of time, and this could take a while. The water needs to be about 30 centimeters deep. If you only have access to a cold water source, doing it the day before allows the water to warm up to room temperature which is more pleasant for the animal. If warm water can be added to raise temperature to about 26C, this would be even better and then water filling could be done an hour or two before the lab begins. The water will also need to be made opaque using powdered skim milk, but as this can develop an unpleasant odor if left too long, this can be done just before the lab begins. Make sure you have some dry towels handy to dry off the rat after each trial. For the Exploration test, collect 4 large, heavy, durable, and distinctive objects to use (e.g., Glass jars, desert bowls, coffee mugs, brass weight). You don’t want objects that the rat can damage, move, get caught in, or that will cause injury. Set them up in a square pattern in the middle of the arena (Poucet et al., 1986). These tests will use the Any-Maze software. You can download this software for free from the supplier to become familiar with its operation (http://www.anymaze.com). Your TA should have the any-maze protocols set up for these tests ahead of time.

Test: Watermaze For the watermaze test, start the capture program, and make sure the watermaze template has been properly set up. Start the capture program and then place the animal in the water. Do this by supporting it with your hand as you lower it slowly into the water tail-first. Choose a variety of location. Allow it to swim for 60 seconds, or until it finds the platform, whichever occurs first. If after 60 seconds it has not found the platform, carefully grasp it around the middle, lift it up, and place it on the platform for 15 seconds. Allow the rat to sit on the platform for 15 seconds so that it can orient itself. Run 4 or 5 more trials with the rat, allowing it to rest between sessions. Use a different random starting location each time. For the final trial, remove the platform, and allow the rat to swim for 60 seconds. This is the probe trial, where the rat will “tell” you where it thinks the platform should be.

Exploration Test For the exploration trial, place the animal in the arena, and allow it to explore the objects. When it stops exploring the objects, and becomes interested in something else (e.g., it starts grooming), remove it from the maze for a rest. Repeat this a couple of times. For the probe test, do one of the following while wearing gloves: