The traditional eight radial arm maze has many variants that allow mice, rats, and even primates to display their spatial working memory for the arms that they have visited by avoiding re-entry.
Typically, they do so by relying on their memory for the spatial location of visited arms relative to extramaze landmarks in the testing environment. Extramaze and intramaze cues are key to this process.
Separate protocols include the spatial working memory and spatial reference memory tasks.
Note: feeders and end chambers can be added as required as in the image
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Doors for 8 Arms
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The Radial Arm Maze is a widely used behavioral task in neuroscience for studying spatial learning and memory. This test is based on the fact that finding and retrieving food quickly and efficiently is an essential survival strategy for rodents. It was observed that rodents have a remarkable ability to remember spatial locations, especially when baited with food rewards, and this has been adapted into a behavioral task. The maze consists of a central round platform with eight, or potentially more, arms radiating from the center. At the end of each arm is a small chamber, which contains a food reward. The animal will quickly learn to visit each arm only once, obtain the food reward, and then move to a new arm. This task requires use of hippocampal-dependent spatial reference memory, and this ability to remember the location of visited arms can be effected by the administration of certain drugs or disease models.
Olton and Samuelson first used the Radial Arm Maze in 1976. Since then, it has been widely used in behavioral neuroscience because of its ability to measure working and reference memory, its many variations, and its minimally stressful environment. Olton published a series of papers describing the maze and its evaluation of hippocampal-dependent learning over several years (Olton and Samuelson 1976, Olton et al. 1977, Olton and Collison 1979, Olton 1987). Since these initial papers, the maze as been used to study various neurological issues, such as brain injuries, hippocampal lesions, depression, and even the effects of electromagnetic fields emitted from cellular phones on memory deficits (Dubreuil et al. 2003).
The apparatus used for the Radial Arm Maze consists of eight identical arms radiating from a central circular platform. Each arm pathway is approximately 80 cm long and 10 cm wide. At the end of each arm, a small chamber can be added that can contain a food reward. The central platform has an approximate diameter of 30 cm. These measurements can be adjusted to accommodate mice, rats, and small primates. Doors are usually present at the entrance to each arm. The entire apparatus is raised at least 50 cm above the floor. Generally the maze walls are transparent to allow the animals to visualize extra-maze cues.
Fully automated mazes are available which can detect the location of the animal within the maze, open and close doors within the maze, and detect the presence of the food reward in the arm chambers.
The maze should be lit from above to prevent shadows within the maze and lighting should be sufficient to allow animals to see extra-maze cues in the experimental room.
A mounted video camera is used to record the experiments from above the pool. Tracking software can be used to follow the moments of the animals within the maze. Live scoring can also be performed.
The purpose of the Radial Arm Maze is to assess spatial memory and learning in animals, in a control vs. disease model/intervention group, by observing their ability to navigate the arms of the maze and remember which arms they have previously entered. This test can provide information regarding hippocampal-dependent learning, specifically spatial memory. For example, the effects on memory abilities in animal models of aging or neurodegenerative diseases can be tested using the Radial Arm Maze. Typically animals are capable of learning and remembering the location of arms with food rewards using visual cues. This aptitude to remember decreases, and the number of repeat entries or errors increases, in animals with impaired neurocognitive abilities.
There are several versions of protocols to be used with the Radial Arm Maze depending on exactly what data the researchers are looking to obtain. The fully-baited version of the maze, which asks the animals to visit each arm only once per trial, has been commonly used to study hippocampal lesions or degeneration, and to determine the involvement of a specific gene or protein in spatial memory (Dubreuil et al. 2003).
Pre-Training for the Fully-Baited Radial Arm Maze
Prior to testing, animals need to be familiarized with the maze. This can be done over a period of several days. On the first day, animals are placed in the maze in small groups for twenty minutes. During this time, they are free to explore the maze and can food rewards scattered throughout. Fruity Pebbles (Post Foods) work especially well as food rewards for rodents. On the subsequent days, food rewards were only placed at the ends of the arms. During these familiarization sessions, the doors at the entrances to the arms should be open and closed regularly to accustom the animals to the movements and noise.
Evaluation of Spatial Learning and Memory Using the Radial Arm Maze
To begin the training and testing process, prepare the apparatus by ensuring it is clean and close the doors to each arm. Place a food reward in the chambers at the end of each arm. Set up any visual cues within the testing area. Bring animals into the room, and allow an acclimation period if necessary.
For a fully-baited maze training procedure, animals are tested daily for ten to twenty consecutive days. The chamber at the end of each arm contains a food reward, and the animals should learn to visit each arm only once per session. Place one animal in the center of the maze while all eight doors are closed. Open the doors simultaneously and allow the animal to freely explore the maze for ten minutes. Record the number of arm entries and errors, which occur when the animal enters the same arm more than once during a testing session. End the trial prior to ten minutes if the animal enters all eight arms or the animal makes sixteen arm entries. Clean the apparatus between trials to eliminate olfactory cues from previous animals.
Since Olton and Samuelson introduced the Radial Arm Maze in the mid-1970s, researchers have adapted various modifications to the maze to study particular aspects of spatial learning and memory. While each modification allows for the collection of specific data and can help differentiate between working and reference memory, the different versions of the Radial Arm Maze all provide measures of the spatial learning, memory, and overall cognitive function.
Similar to the fully-baited version detailed above, there is also a confinement/deley version of the maze (Dubreuil et al. 2003). In this task, the entry of the animal into one arm triggers the doors of the other seven arms to close. The animal is free to explore the one arm, obtain the food reward, and then return to the center of the maze. After the animal returns, the eighth door closes, confining the animal to the center for at least ten seconds. After this delay, all eight doors open, and the process is repeated for the subsequent arm entries. Other groups have utilized longer delay versions as well to test how long the animals can remember spatial locations (Suzuki et al. 1980, Bolhuis et al. 1986, Strijkstra et al. 1987).
Other versions of the maze have also been adapted, some of which use a set up where the maze is not fully-baited. Using a partially-baited maze requires a training phase, delay, and test phase, all of which occur in the same session. During the training phase, four of the arms contain a food reward and the doors to these arms are open while the doors to the remaining arms are closed. The animals are free to enter the open arms and obtain the food rewards. After doing so, the animal is confined to the center of the maze for a set time delay. When the test phase begins, all eight doors will then open and food rewards are now located in the arms that were previously blocked. The animals are expected to enter the arms that had not been visited during the training phase. This version of the Radial Arm Maze has been used to study cognitive dysfunction and its relationship to depression-like symptoms (Richter et al. 2013).
The data obtained from the Radial Arm Maze generally consists of following measures: number of total arm entries (the animal places all four paws in an arm), number of correct arm entries (the animal enters a novel arm not previously entered), and number of error arm entries (the animal enters an arm previously entered). The time between retrieving food rewards can also be recorded as a measure of activity and willingness to explore. As the animal learns that entering a new arm results in a food reward, the number of error arm entries should decrease. These values can simply be graphed and compared across a sham control group and a disease model/intervention group, as shown for one group below:
In addition to counting entries, a memory score can be calculated using the following formula:
This score describes the memory performance on a scale from -1 to 1, with a score of 1 reflecting a perfect score of only entering novel arms (Richter et al. 2013). By visualizing scores over several days of testing, memory scores should improve, as shown in the example graph below.
Using graphs similar to these to compare arm entries between different disease or treatment groups allows for easy visualization of the effect on spatial memory and learning. Animals in the controls groups should show significant improvements in their correct arm entries and memory scores. Animals as disease models of neurodegenerative disorders, for example, should show a much slower learning curve with more error entries, even after several trials. Generally, animal cohorts of 20-30 animals are sufficient to obtain p-values of <0.05 using ANOVA, chi-squared test, and post-hoc tests (Dubreuil et al. 2003, Richter et al. 2013).
A major strength of the Radial Arm Maze is the minimal stress placed on the animals. Other mazes that also test spatial learning and memory, such as the Morris Water Maze subject the animal to significantly more stress as it must be submerged in water, swim in order to survive, and search for an escape platform (Hodges 1996). The Barnes Maze is an additional maze used to test spatial learning in animals, and does not require immersion in water or forced swimming. The Radial Arm Maze also uses food rewards as task motivation, rather than escape and survival, which intrinsically places less stress on the animals (Hodges 1996). The absence of significant stressors and familiarization with the maze prior to testing allow for better observations of working and reference memory in the animals as they perform in the maze. However, the Radial Arm Maze requires more training and is more time-consuming than other mazes that test similar measures.
As with all mazes that measure aspects of learning and memory, it is important to remember that many different processes play into behavior in the maze. The Radial Arm Maze has been used with various different modifications, both in the experimental procedures and analysis, that allow researchers to differentiate between working and reference memories. Other modifications can also be used to answer questions regarding how long the animals can remember the location of specific arms and how visual cues aid the animals in forming spatial memories. In many cases, the Radial Arm Maze is used in conjunction with other mazes to study disease models or transgenic animals and gain a fuller understanding of spatial learning and memory.
• The Radial Arm Maze is an extensively used maze to test spatial learning and memory
• This task asks animals to retrieve food rewards at the end of each of eight arms without visiting an arm more than once
• Different groups have adapted this maze in order to collect data regarding working or reference memory and there are many modifications available, both in regards to experimental protocol and data analysis
• Animals in control groups show rapid learning as they remember the location of the arms from which they have retrieved the food reward, while in comparison, animals as disease models of neurodegenerative disorders or brain injuries show a much slow learning curve with lower memory scores