Answer: The Barnes maze is a rodent behavioral test used in the research laboratory for studying memory.
In neuroscience research, sometimes scientists develop new techniques to study specific cognitive outcomes. Learning and memory are very important tasks that are important for humans, especially in the context of brain injury or Alzheimer’s disease. It is therefore helpful to invent memory tests using nonhumans, like rats and mice, so that the scientists can more easily test new drugs that might be able to treat amnesia.
The Barnes maze is one such test. This test is a behavioral test, since the rat or mouse is put into the maze, and how they perform is recorded. The maze itself is a large circular platform. At the perimeter of the maze are a number of holes which are spaced evenly apart. Barnes mazes may have between twenty and forty holes. One of these holes has a small tunnel connected to it, which allows the animal to leave the maze. This is the exit. The rat is placed in the middle of the Barnes maze, its position is tracked, and the time it takes to reach the hole containing the tunnel is recorded.
In terms of the research design, the time spent on the maze is considered to be the dependent variable.
There are also visual cues shown to the animal, which help the animal orient themselves to their surroundings. These are all visible from the center of the maze. Some of these visual cues may include the presentation of different colored shapes, such as posters on the wall.
Memory is a complex cognitive function which has many different forms. The main type of memory being assessed in the Barnes maze is called spatial or navigational memory. Navigational memory is the type of memory that allows the animal to associate a position in space (relative to certain visual cues, for example) with the exit. If the animal has a good spatial navigational memory, they will continue to perform better on the maze (less time spent until exit) the more they practice.
The Barnes maze takes advantage of a behavior that is intrinsic to small prey mammals like rats and mice. In general, these animals show a natural avoidance to wide open spaces. In the wild, open spaces like a empty grassy field are very risky environments for these animals. Aerial predators, such as hawks or owls, are more capable of spotting their prey if there is no surrounding cover. Naturally, rats and mice will be attracted to spaces that are darker or more enclosed, such as a log or an underground tunnel.
In terms of the Barnes maze, these natural behaviors are tested. The center of the maze is usually brightly lit, which resembles a grassy field. The escape tunnels are surrounded on all sides, which resembles an underground tunnel. So, the animals prefer to find the tunnel as quickly as possible since it provides the feeling of safety. Therefore, researchers might say that the Barnes maze offers good ethological validity, since it mimics what the animals would seek in the wild.
Many Barnes maze setups are equipped with overhead cameras, which are used to track the path that the animal takes. This provides a little bit more information compared to simply recording time to exit.
The maze is named after Dr. Carol Barnes, who first described her behavioral test in the 1979 publication Memory deficits associated with senescence: A neurophysiological and behavioral study in the rat.
Barnes maze compared to Morris water maze
The Barnes maze is similar to another behavioral test for navigational memory called the Morris water maze. In the Morris water maze, the animal is placed in a swimming pool filled with opaque water. The exit is a platform hidden beneath the surface. Like the Barnes maze, the surroundings contain various visual cues which help the animal form spatial memories. With time and practice, animals start to reach the exit sooner.
The advantage of the Barnes maze is that it is a dry land test. Some experimental paradigms require the use of electronics, such as embedded stimulator probes, cranial window cameras, or tiny electrophysiology rigs. In these experiments, water poses a risk of short circuiting the equipment. However, since the Barnes maze is entirely dry, risk of damage to the electronics is less of a concern.
Another advantage of the Barnes maze is that it doesn’t require the degree of physical fitness that swimming does. The Morris water maze requires that the animal can swim for potential minutes at a time, which may introduce another confounding variable. Walking and exploring the Barnes maze is less demanding, allowing the researcher to focus on the variable of interest, which is spatial navigational learning.
Performance on the Barnes maze and the Morris water maze are dependent on circuits through a brain structure called the hippocampus. Injury to the hippocampus is known to disrupt spatial memory formation. Surgical lesions of the hippocampus reliably impair performance on both of these tasks, causing the rat or mouse to reach the exit slower, even after several trials have been run.
Barnes Maze protocol
While different research groups will use slightly different protocols, the following is one described in Pitts et al., 2015.
The TSE Systems Barnes maze apparatus is a circular white platform with 40 holes equally spaced along the perimeter. One of the holes is designed the escape tunnel. This escape tunnel is not changed.
The mouse is placed in the center of the platform for 3 minutes. Time until the animal reaches the exit is recorded. If they do not find the exit, they are placed in the exit for 15 seconds.
This was repeated twice a day for a total of 10 days.
The data from two different groups were analyzed using a two-way repeated measures ANOVA.
Pitts et al. discovered a decrease in latency (increase in learning) with increased trials. The full text for this protocol can be found here: Competition between the Brain and Testes under Selenium-Compromised Conditions: Insight into Sex Differences in Selenium Metabolism and Risk of Neurodevelopmental Disease.
Source: Barnes Maze Procedure for Spatial Learning and Memory in Mice
