The Barnes maze is a spatial memory task that requires subjects to learn the position of a hole that can be used to escape the brightly lit, open surface of the maze. The animal is placed in the center of an aversive (brightly lit) open platform. An escape tunnel is fixed below one of the holes. During acquisition the animal is supposed to learn the spatial location of the escape hole that serves as positive reinforcement. Extra-maze cues have to be available in the environment to allow for spatial orientation. The trial is terminated after a predefined duration has elapsed or after the animal has disappeared into the escape tunnel and the data acquisition stop. The parameter generated is the so-called escape latency. In addition to escape latency the total distance travelled as well as the average speed is calculated automatically from the movement data.
- The maze platform is white, circular, 0.95 m in diameter, and has 12 evenly spaced 10-cm holes at its edges. The platform is suspended approximately 1.4 m off the ground, which is high enough that rodents don't spontaneously jump from the platform to the ground.
- A darkened escape chamber similar in texture to the animal’s home-cage is maintained under one of the holes at the edge of the platform. This escape chamber remains in a constant position relative to the room throughout testing, although the platform itself is rotated so as to confuse any possible scent trails.
- The platform is surrounded by an Opto-Varimex-Magnus animal monitoring system (Columbus Instruments, Columbus, OH), which records the animal’s position, the distance the animal moves, and the amount of time the animal spend ambulating, resting, and moving but not ambulating (twitching, making circular movements, etc.).
- Animals is habituated to the maze for 1 day prior to the beginning of testing. This habituation consists of placing the animal in the escape chamber for 2 min, then placing it directly in the hole that lead to the escape chamber and allowing it to remain in the chamber for another 2 min, and finally placing the animal in a small, four-walled chamber containing the escape hole that allow the animal to escape from this one-choice test. The amount of time that an animal take to enter the hole in the one-choice test is measured as a control for the motivation to enter the hole.
- a) Testing begin by placing the animal under a bucket in the center of the circular platform in a room that was brightly lit (, 40W fluorescent bulbs in ceiling lights) and rich in consistently located spatial cues (including a large metal door, two prominent posters on one wall, some abandoned computer equipment, and the experimenter’s desk).
- b) When the bucket is lifted the animal is monitored as it find its way from the center of the platform to the escape hole. Each animal is allowed a maximum of 3 min in the maze at each trial. Errors (indicated by the animal placing its nose or forepaws at the edge of a hole that did not lead to the escape chamber) and the distance and time traveled to get to the escape hole are measured at each trial. On reaching the escape hole, the animal is allowed to remain in the escape area for 2 min, removed to its cage for a 15-min rest period, and then returned to the maze for another trial.
- c) After an initial test where the animal don't know the position of the escape hole (designated Trial 0), the animal is tested 4 times per day for 4 days.