The Barnes maze is a tool used in psychological laboratory experiments to measure spatial learning and memory. The test subjects are usually rodents such as mice or lab rats, which either serve as a control or may have some genetic variable or deficiency present in them which will cause them to react differently to the maze.
Contents |
The Barnes maze consists of a circular table with 20 circular holes around the circumference of the table. Under each hole is a slot for a box, called the drop box. The goal of the maze is to reach the drop box, which is a box that has an open top, and can be reached through one of the holes in the top of the table. Exposure on the surface of the table serves as negative reinforcement, motivating the test subject to seek shelter. The only shelter available is the drop box, to which the test subject must flee. In order to accustom the test subject to the maze, it is guided into the drop box by a sheltering hand. After four to five runs, a normal test subject can quickly make a beeline for the drop hole. Fixed visual cues set up around the platform serve to orient the rodent during the trials.
Performance is typically measured by number of errors the rodent makes, i.e. the number of times it pokes its nose into, or hovers its head over a circular hole that does not contain the drop box. The rate of decline in the number of errors/trial is measured across subjects. Other performance values can also be measured, for example the strategy used by each rodent can be scored as random (randomly checking each hole), systematic (checking each hole in a pattern) or spatial (direct movement to the hole with the drop box). An experiment done on Octodon degus reveaaled that spatial navigation is influenced by gender differences in nocturnal rodent species. A 16 months old male and female were tested using the Barnes circular maze.In the first ten days, the acquisition sessions of the rodents were 4minutes long everyday. After seven days, a retention test was performed. The acquisition session consisted of four daily 4min trials, during 10 days. Seven days later, the retention test was performed. To avoid the effect of hormonal fluctuation on spatial navigation, both the acquisition and the retention tests, were performed in 21-day regular cycling females in a period that corresponds to the diestrus phase of the estrus cycle. At the beginning of the acquisition, female degus were significantly slower than males to find the escape hole, but the situation reversed afterwards. Moreover, during the course of acquisition, females made significantly less reference memory errors, working memory errors as well as omission errors, than males. In both sexes, motivation and learning ceiling effects were reached at days 5–6 of the training. During the acquisition, females used more frequently a spatial strategy, while males preferably applied either serial, random or opposite strategies. The observed cognitive differences between male and female O. degus existed only during the acquisition period but not during the retention, indicating that acquisition and consolidation are differently influenced by gender (Popovic,Natalija, 2010).
One problem with the Barnes maze is the constant need to clean up after each trial. When nervous, most rodents will urinate and defecate on the table, necessitating the experimenter to clean up the entire table with disinfectant. Also, other animals who have not yet been tested cannot be allowed to witness the experiment in action, or they will have prior knowledge to the nature of the experiment, which will allow them to find the drop box more easily. Another consequence of untested animals witnessing the experiment is pre-experiment nervousness, which will make the animals experience more stress, and will make it harder for the experimenter to take hold of the animal. All of this shows a high level of comprehension in the animals of what is happening or will eventually be happening to them in the future. Also, the use of vivid lights can also instigate a slight drawback if a video camera, computer and tracking software are used to document performance; most tracking methods are extremely sensitive to light reflections from the lit surface. [1]