- Four beacons are suspended 25 cm above the water surface.
- One of the beacons is always suspended directly over the hidden platform
- The hidden platform is always located in the same quadrant of the pool called the target quadrant
- The hidden platform can be located in any of three different positions along the center radius of the target quadrant (configuration B,C,D and E)
Studies in humans have shown that damage to hippocampus causes temporally graded retrograde amnesia. However in rats, experiments with Morris water maze has shown that leisons in hippocampus impairs recent and remote spatial memory similarly
Clark et al.(2007) modified the standard water maze in which rats employ a navigational beacon to guide their search, abandoning a strictly spatial strategy as in standard MWM
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With scientific discoveries in spatial memory and navigation constantly advancing, the Multiple Beacon Maze offers a novel modification to the traditional Morris water maze (Morris, 1984), making possible more specific testing procedures addressing different aspects of spatial behavior.
The multiple-beacon maze consists of the traditional water maze design, with added beacon components placed above the overall structure. Subjects, while training to swim towards an escape platform, also learn to associate one of four identical beacons to the location of the escape platform, pointing out in which quadrant and in which area within the particular quadrant. In this manner, rodents are forced to acquire spatial information to choose the correct beacon and are then free to swim towards the beacon without needing to navigate or track its position in the maze.
The multiple beacons, with which subjects associate the escape platform’s location, provide opportunities for evaluation of spatial memory irrespective of the ability to navigate towards the target space (Clark et al., 2007). With the association of beacons to the location of the escape platform during pre-training, rodents abandon spatial strategy and instead use knowledge about the platform’s location relative to the beacon to guide them in the task. With its additional components, the multiple-beacon maze allows for the evaluation of rodents based on spatial memory independent of navigational ability.
Apparatus and Equipment
The multiple-beacon maze consists of four identical, adjustable beacons fitted with bulbs and placed above a traditional Morris water maze setup. The tub or tank of opaque water is divided into four quadrants, with a beacon permanently suspended 25 cm above the water surface in each quadrant. An escape platform is hidden within the target quadrant, and its position can be varied in medial, intermediate, and lateral locations along the quadrant’s center radius.
During behavioral training, rodents are familiarized with general water maze procedures and trained to swim towards a hidden escape platform with the guidance of overhead beacons. In each initial trial, the subject swims freely towards the target quadrant, and when it reaches within 20 cm of the hidden platform, the platform is raised from a lowered to an accessible position.
In each trial, the position of the escape platform within the same target quadrant along with its guiding beacon is pseudo-randomized for the learned association. During these behavioral trials, rodents are first forced to dwell near or within the target area before being reinforced by the presence of the escape platform in order to correctly identify and learn the specific location. Spatial learning is tracked across training with the use of Noldus Ethovision XT.
Past research in spatial memory has looked into scientific advancements in brain lesions in the hippocampus, pharmacological therapy, and so on. Following behavioral training with the multiple-beacon maze, rodents may thus be divided into experimental and control groups for testing.
The rodent’s performance is measured based on two variables, the first of which is the percentage of time spent in the target quadrant where the escape platform was located during pre-trials. This variable is able to suggest whether the rodent’s spatial memory is intact or not. Second, the percentage of time spent in the area underneath the target beacon, compared to the two other possible locations within the quadrant, is also documented. This may be able to tell whether the rodent has retained the ability to use the beacons as guidance in locating the escape platform.
Data can either be recorded acquired by a timer or video tracking system like Noldus Ethovision XT.
The multiple-beacon maze offers a wide array of possibilities in the assessment of spatial navigation by distinguishing between different categories (O’Keefe and Nadel, 1978), such as mapping locations and associative stimulus-and-response learning (Timberlake et al., 2007). It has been a particularly useful tool in the study of hippocampal lesions and their effects on spatial memory and performance/navigational ability.
The sample data is represented by plotting the mean percentage of time spent in the area underneath the guide beacon in medial, intermediate, and lateral trials by lesioned and non-lesioned mice. As seen from the graph, the lesioned group had a significantly impaired performance compared to the control group, suggesting that lesioned mice had a lower tendency of using the beacons as a guide for reaching the escape platform’s location.
Strengths & Limitations
The added component of guide beacons in the multiple-beacon maze serves to segregate the evaluation of spatial memory and navigational performance into its key aspects. The advantage offered by the multiple-beacon maze’s design is the spatial information that rodents acquire from guide beacons, distinct from the navigational component of the task wherein rodents track their movements as they travel in space.
Another advantage provided by the multiple-beacon maze is the strength of learning that rodents experience. Findings from Clark et al., 2007 study on the hippocampus and spatial memory suggest that the multiple-beacon setup offered an advantage to rodents that was not made available in traditional Morris water maze setups. Therefore, the rodents’ performance during training was vastly improved when compared to rodents trained in standard versions of the water maze.
Summary and Key Points
- The multiple-beacon maze is an innovative version of the traditional Morris water maze design, presenting an additional modification of four identical beacons suspended above the water maze
- The multiple beacons guide rodents in locating where the target quadrant and escape platform lies and thus provides another dimension for observation and analysis of spatial memory, independent of rodents’ navigational ability
- The tool has helped facilitate the study of specific effects of hippocampal lesions on spatial memory
- The apparatus consists of the traditional water maze setup with four identical beacons suspended 25 cm above the water surface and equidistant from one another
Clark, R. E., Broadbent, N. J., & Squire, L. R. (2007). The hippocampus and spatial memory: findings with a novel modification of the water maze. Journal of Neuroscience, 27(25), 6647-6654.
Timberlake, W., Sinning, S. A., & Leffel, J. K. (2007). Beacon training in a water maze can facilitate and compete with subsequent room cue learning in rats. Journal of Experimental Psychology: Animal Behavior Processes, 33(3), 225.
O’keefe, J., & Nadel, L. (1978). The hippocampus as a cognitive map. Oxford: Clarendon Press.