Testing representation in mice through maze conditioning and reward motivation

Abstract

In this experiment, mice were conditioned to complete a maze by using a reward system. Upon completion, they were given access to a playground area in which they were allowed to spend a certain amount of time. Throughout the experiment, the maze entrance and playground entrance were each associated with a certain object. The mice were then placed in an intermediate area in which both of the associated objects were placed near entrances located at different ends. The time spent near each entrance was recorded and the expected result was that the mice would spend more time near the entrance associated with the reward. This tested whether the mice complete the maze because of the associated reward or because they were conditioned to run the maze. The results showed an increased amount of time spent towards the entrance associated with the reward.

Introduction

Representation is the presence of a mental image or goal and it is associated with an animal’s intellect or ability to learn. Mice have commonly been trained to run and complete mazes to test the idea of learning curves and performance. Whether mice possess a mental image of their goal or simply run the maze because they have been conditioned to do so, is a somewhat difficult subject to test. This experiment will test the presence of representation in mice.

The experiment consisted of four mice that were conditioned to complete a maze. The entrance to the maze and the entrance to the reward area were each associated with different objects. Initially, the mice were placed in an intermediate area and the entrance to the maze was opened. At the end of the maze there was an entrance where their reward was placed. The reward was access to a playground area for a certain amount of time. After several trials of completing the maze, the mice were then placed in the intermediate area where the object associated with the maze entrance and the object associated with the reward entrance were placed at different ends. Their time spent near each entrance was recorded. The hypothesis is that mice will spend more time near the entrance associated with the reward even though they have been conditioned to complete the maze in order to reach their reward.

Materials and Methods

First, four mice were introduced to a simple double T-maze. Two different entrances to the reward area were placed at different ends. These entrances gave the mice access to a playground. The playground consisted of toys, food, a wheel, tunnels, cotton bedding and different objects the mice could climb on. Each mouse was designated a specific entrance with the other entrance closed off. A green mat was placed at their designated entrance, so the mice would learn to associate entrance to the maze with this object. When optimal performance time was reached completing this simple T-maze, the mice were introduced to a more complex maze.

Figure 1: The setup of the initial T-maze used. Two mice were designated exit 1 and two mice were designated exit 2. Only their designated exit allowed them access to the reward, with the other exit closed off.



For the second maze, the mice were placed in an enclosed intermediate area where an entrance to the maze was located. At the maze entrance, a wooden block was placed so the mice would associate the maze entrance with this object. The mice were then conditioned to complete the maze. The same reward was given with the associated green mat placed at the playground entrance. The mice were again designated a specific playground entrance. This designation would prevent the mice from completing the maze by following the scent left by the previous mouse. Instead, they would have to complete the maze by remembering their designated path.

Figure 2: Design of the second maze used. The four experimental mice were placed in the intermediated area located at the maze entrance. A wooden block was placed in front of the maze entrance and a green place mat was placed in their designated exit. Only their designated exit gave them access to the playground, with the other exit closed off. Only their designated exit contained the place mat.

After 35 trials of completing the maze, the last part of the experiment was performed. The mice were placed in the intermediate area and both of the associated objects were placed at different ends. They were given access to the reward using this new entrance located in the intermediate area. The four mice were then allowed to complete the maze twice, but with no reward given. After these two maze runs, the mice were again placed in the intermediate area. A line was drawn to divide the intermediate area in half, with one end having the wooden block and the other end having the green mat. The time spent in each section was recorded for a minute. This process was repeated five times over a five day period.

Figure 3: Mice were placed in the intermediate area and allowed access to the reward through this new entrance. They were then allowed to run the maze but with both exits closed off and no access to the reward (playground). For the last part of the experiment, the mice were placed in the enclosed intermediate area and their time spent near each entrance was timed for one minute.

As a control, four mice that had no previous exposure to the maze or the associated objects were also placed in the intermediate area over this five day period. Their time spent in each section was recorded for a minute. This would test whether there was any significance or other variable present to account for the results of the experimental mice

Data and Results

 Figure 4: Maze trials completed by mouse A.

 Figure 5: Maze trials completed by mouse B.

Figure 6: Maze trials completed by mouse C.

Figure 7: Maze trials completed by mouse D.

Figure 8: The average time each of the experimental mice spent near the two entrances. The average times were taken from the five trials.

Figure 9: The average time each of the control mice spent near the two entrances. The average times were taken from the five trials.

Table 1: Collected data fromboth experimental and control mice.

Mouse	Average time to run maze	Median time to run maze	Average time spent near reward entrance	Average time spent near maze entrance
Experimental
A	17.0	14.0	44.4	15.6
B	20.1	15.0	42.6	17.4
C	16.5	14.0	37.2	22.8
D	14.1	9.0	40.4	19.6
Average	16.9	13.0	41.2	18.9
T-test using average times			P-value=.002768
Control
1			28.2	31.8
2			30.4	29.6
3			30.4	29.6
4			26.2	31.8
Average			28.8	30.7
T-test using average times			P-value=.16168
T-test using time values between experimental and conrol
			P-value=.004341	P-value=.00441

Discussion

The data collected support the hypothesis that the mice will spend more time near the entrance associated with their reward. The performance curves demonstrate that the experimental mice were successfully conditioned to run the maze. The different times between the experimental and control group show that the experimental mice associated the reward with the green place mat and the increased amount of time spent near their reward entrance may indicate that mice possess a mental representation of their goal as opposed to completing a procedure they have been conditioned to perform.