The present protocol describes a reconfigurable maze, a unique system for testing spatial navigation and behavioral phenotypes in rodents. The adaptability of this maze system enables the execution of various experiments in a single physical environment. The ease of structural rearrangement generates reliable and reproducible experimental results.
Several maze shapes are used to test spatial navigation performance and behavioral phenotypes. Traditionally, each experiment requires a unique maze shape, thus requiring several separate mazes in different configurations. The maze geometry cannot be reconfigured in a single environment to accommodate scalability and reproducibility. The reconfigurable maze is a unique approach to address the limitations, allowing quick and flexible configurations of maze pathways in a repeatable manner. It consists of interlocking pathways and includes feeders, treadmills, movable walls, and shut-off sensors. The current protocol describes how the reconfigurable maze can replicate existing mazes, including the T-shaped, plus-shaped, W-shaped, and figure-eight mazes. Initially, the T-shaped maze was constructed inside a single experimental room, followed by modifications. The rapid and scalable protocol outlined herein demonstrates the flexibility of the reconfigurable maze, achieved through the addition of components and behavioral training phases in a stepwise manner. The reconfigurable maze systematically and precisely assesses the performance of multiple aspects of spatial navigation behavior.
Spatial navigation is a fundamental ability of an animal to identify a suitable route to a targeted goal. Various cognitive processes, such as decision-making, learning, and memory, are needed during navigation. Utilizing these processes permits experiential learning when determining the shortest route to a goal. Maze tests are used to investigate the behavioral and physiological mechanisms of spatial navigation1. For example, the T-shaped maze2,3, plus-shaped maze4, radial arm maze5,6, and figure-eight maze7 assess spatial navigation behavior, including cognitive variables such as decision-making8 and anxiety9.
Each maze shape has advantages and disadvantages, requiring multifaceted experiments using multiple maze tasks to assess specific learning and memory10,11. For example, the spontaneous alternation task, in which an animal selects between the left and right arm without requiring learning, is a typical spatial working memory task that can be assessed with the T-shaped and Y-shaped mazes12. The plus-shaped and radial arm mazes, which use head direction and external cues, are used to determine goal-oriented navigation ability13. The figure-eight and modified T-shaped mazes, which separate the routes on selection and return, are used to evaluate spatial working memory tasks by analyzing the navigation function by trajectory14,15.
It can be challenging to maintain consistency among mazes when using several mazes in one experiment. Rodents are thought to use visual cues for navigation16,17,18; olfactory19,20 and somatosensory21 modalities may also be used for spatial cognition and may contribute to navigation ability. If a series of maze experiments are conducted using different spaces, layouts, dimensions, and materials, these variables may influence the navigation strategy of the rodents. Spatial navigation studies require the strictest control possible of these variables; however, maintaining a standardized maze apparatus for various shapes or rebuilding the maze for each experiment can be costly. These difficulties prevent a systematic way of conducting a series of experiments within the same laboratory.
To combat configured limitations in previously established maze structures, a maze system that can be configured in various shapes in a single physical environment22 is described here. The "reconfigurable maze" combines standardized parts, providing a highly repeatable, reproducible, flexible, and scalable testing environment. This article describes the ability of a reconfigurable maze to evaluate spatial navigation in rodents.
All procedures were approved by the Doshisha University Institutional Animal Care and Use Committees. Three male Long-Evans rats, aged between 24 and 28 weeks (at the start of behavioral training), with body weights of 300-350 g, were used for the present study. The rats were housed individually in home cages (20 cm x 25 cm x 23 cm) on a 12 h light/12 h dark schedule, with the light period starting at 08:00 am. The animals were obtained from a commercial source (see Table of Materials).
1. Maze system components
NOTE: The maze system (including all the components, steps 1.1-1.5) (see Table of Materials) must be mounted in a shielded room covered with copper mesh (4 m x 5 m for rats and 1.8 m × 3.0 m for mice) for simultaneous use of electrophysiological neural activity recording. The maze needs to be elevated at a fixed height from the floor (55 cm for rats and 34 cm for mice).
2. Evaluation of special navigation of rodents in the reconfigurable maze
NOTE: An animal behavior experiment was conducted using the reconfigurable maze (developed in step 1).
3. Behavioral performance and data analysis
Some parts of the reconfigurable maze used standard maze constructions described in previous studies3,4,7,26,27. Here, the linear track, T-shaped, W-shaped, and figure-eight mazes were reconfigured in the same physical environment (Figure 4A-D). To demonstrate that the reconfigurable maze could smoothly implement the desired behavioral test by gradual and rapid scaling, the protocol utilized for representative results included four training phases (Figure 5A).
In phases I and II, rewards were received by poking Feeder R after poking Feeder A. In phases III and IV, the reward was received by poking Feeder R after poking Feeders A and B, in that order. In phase IV, the poking of Feeder A triggered the rotation of the treadmill, and Feeder B could only be accessed after 5 s of forced running. In the test phase (delayed alternation task), the procedure was similar to that of phase IV, but Feeder R was in the arms at either edge of the T-shaped maze, and rats were rewarded by poking the opposite feeder from the previous phase. Rats were able to move in response to the length and shape of the extending pathway and changing feeder sites (Figure 5B). All phases were performed in 30 trials, with each trial defined as an instance of the rat reaching Feeder R. The task duration spent by the three rats completing 30 trials in each phase is shown in Figure 6A. Repeated measures ANOVA confirmed that the task completion time of rats differed among phases (F (4, 8) = 16.98, p < 0.05, Greenhouse-Geisser corrected28). The rats were able to adapt flexibly to changes in pathway length and reward conditions. In the test phase, which was conducted the following day, all rats asymptotically approached the high percentages of correct choice responses within 3 days (Figure 6B).
Several experimenters constructed the mazes to confirm that such a stepwise maze expansion could be performed rapidly (Figure 6C). In this article, the time of the accompanying parts (treadmill, feeders) were added to the morphing time of the pathway in the previous report22 in order to measure the maze construction time practically. Using the procedure for the delayed alternation task (Figure 5A), five experimenters changed the maze from the phase II shape to the test phase shape. The time converged to 67.80 ± 3.03 s (mean ± SE) on the third trial. The test included experimenters who had used this maze system for several years and those who had rarely used it.
Figure 1: Elements of the reconfigurable maze. (A-E) Tower with baseplate and corresponding parts for rats. (F,G) The fixing method of the baseplate is different for rats and mice. Arrows indicate protrusions (white) and bolts (blue). (H) Signal input/output via the controller for fully automated tasks. Please click here to view a larger version of this figure.
Figure 2: Connecting the punching board with the baseplate. (A) Side view of the baseplate, the punching board, and a close-up photo of a protrusion. (B) Top view of the baseplate and the punching board, and a close-up photo of the holes. Please click here to view a larger version of this figure.
Figure 3: Process of T-shaped maze assembly for the delayed alternation task. (A-E) Images of the reconfigurable maze taken from above. The images of the assembly process are in order from left to right. The red arrows indicate the positions of the newly assembled treadmill (C), feeders (D), and movable walls (E). Please click here to view a larger version of this figure.
Figure 4: Several maze shapes in a single environment. Images of the reconfigurable maze. (A-D) Reconfigurable maze test for rats. The pathway parts were reconfigured into several shapes in a single environment, with reference to the location of the pathway parts enclosed in red in (A). (E-F) Reconfigurable maze test for mice. These mazes were placed with feeders (red arrows) and movable walls (green arrows) at any location. Please click here to view a larger version of this figure.
Figure 5: Maze expansion and trajectories of a rat. (A) The maze shape changes gradually during the train and test phases of the delayed alternation task. The type of feeder used in the task is indicated by a colored box. (B) Running trajectories of a representative rat. Each trajectory corresponds to the phase in (A). Please click here to view a larger version of this figure.
Figure 6: Performance of maze experiments. (A-B) The behavioral performance for 4 days, from the start of training to the end of the test. (A) Task completion time for each training phase and the first day of the test phase (n = 3). (B) The percentages of correct choice responses (mean ± SE) in the delayed alternation test. Dotted lines indicate chance levels. SE: standard error of the mean. (C) Reconfigurable maze assembly time. The linear track was modified into a T-shaped maze (top). The modification included the addition of pathways (white square), feeders (black square), and a treadmill (green square). Five experimenters performed three trials each (bottom). Before the test, the expert user (Experimenter 1) performed one trial as an example. All trials were performed on the same day. Please click here to view a larger version of this figure.
The reconfigurable maze enabled us to conduct a variety of maze tasks in a single environment. Equally spaced holes on the floor and an interlocking system coordinated by towers with baseplates guaranteed a high degree of repeatability and reproducibility. In addition, the structure could be easily attached and detached, and the desired maze shape could be configured instantly, functioning as an efficient, flexible, and scalable system.
The reconfigurable maze allowed the animals to learn rapidly. In conventional maze experimental environments, it can be difficult to reconfigure the length and shape of the pathway, and conducting tests that combine multiple mazes is time-consuming. As demonstrated in this study, the reconfigurable maze enables maze extension in a step-by-step manner, where training post-modification of complex behavioral tests is conducted efficiently in a single day (Figure 6A,B). Furthermore, it is easy for the experimenter to make modifications. In this study, the maze assembly time was measured in multiple trials, and the experimenters consistently completed the reconstructions in about 1 to 2 min (Figure 6A).
A major advantage of this maze system is that it allows for fine-tuning the shape of the maze. Because the floor is filled with punching board holes, it is possible to perform flexible maze experiments that would be difficult to achieve with conventional maze systems. In the delayed alternation task performed in this study, the rats initiated the delay and exited the delay area by poking (Figure 5A). Placing two feeders nearby, as we have done here, is difficult in a conventional maze system with a fixed geometry. Additionally, this maze system enables counterbalanced modifications; for example, the position of Feeder B can easily be replaced on the opposite side (Figure 5A). This advantage also allows for the replication of maze configurations across laboratories. Several mazes are used for the delayed alternation task, including the figure-eight maze, the Y maze, and the W maze26,29,30. The reward zone, delay area, and delay method also differ from study to study23,31. With the reconfigurable maze, all of these different mazes can be created in a single physical environment and reproduced in different laboratories. If this system becomes widespread, it could lead to the standardization of maze tasks between laboratories.
The reconfigurable maze supports electrophysiological multiunit recordings, which examine the neural correlates that support spatial navigation22. In hippocampal formation, which is considered to play an essential role in spatial navigation, several types of cells have been reported to encode spatial information, such as cells that fire when passing a specific position32 or when approaching the boundary of the external environment33. These cell types change their firing activity based on alterations in distant landmarks16,17,18. This system is ideal for recording neural activity during spatial navigation experiments because the reconfigurable maze can change only the shape of the maze while maintaining the same environment. The reconfigurable maze maintains strict external environment control, a specification pertinent to neural activity experimentation.
The reconfigurable maze provides an optimal environment for maze experiments, with some caveats. First, the maze is constructed by fitting parts into holes in a punching board, so the angles cannot be changed flexibly. The circular maze (Figure 4E) overcomes this problem to a certain extent, but there are limitations to adding curves and angles to the pathway while ensuring the stability of the maze. In addition, some classical mazes, such as the Morris water maze34 and Barnes maze35, and mazes developed in recent years such as the honeycomb maze36,37, are difficult to construct by combining parts of the reconfigurable mazes. Future efforts should focus on exploring methodologies to merge these maze types with the reconfigurable maze to increase adaptability and cover more cognitive experimentation.
This work was supported by the Japanese Society for the Promotion of Science, Kakenhi grants 16H06543 and 21H05296 to S.T.
Name | Company | Catalog Number | Comments |
3D printer | Stratasys Ltd. | uPrint | |
Arduino Mega 2560 R3 | Elegoo | JP-EL-CB-002 | |
Camera | Basler | acA640-750uc | |
Control box | O’Hara & Co., LTD. / Amuza Inc. | FMM-IF | |
DeepLabCut | Mathis laboratory at Swiss Federal Institute of Technology in Lausanne | N/A | |
Feeder unit | O’Hara & Co., LTD. / Amuza Inc. | FM-PD | |
Free maze system for mice | O’Hara & Co., LTD. / Amuza Inc. | FM-M1 | |
Free maze system for rats | O’Hara & Co., LTD. / Amuza Inc. | FM-R1 | |
Long-Evans Rat | Shimizu Laboratory Supplies, Co. LTD. | N/A | |
MATLAB | MathWorks | Matlab2020b | |
Movable wall for mice | O’Hara & Co., LTD. / Amuza Inc. | FMM-DM | |
Movable wall for rats | O’Hara & Co., LTD. / Amuza Inc. | FMR-DM | |
Pathway and tower for mice | O’Hara & Co., LTD. / Amuza Inc. | FMM-SS | |
Pathway and tower for rats | O’Hara & Co., LTD. / Amuza Inc. | FMR-SS | |
Pellet dispenser | O’Hara & Co., LTD. / Amuza Inc. | PD-020D/PD-010D | |
Photo beam sensors unit for rats | O’Hara & Co., LTD. / Amuza Inc. | FMR-PS | |
Punching board for mice | O’Hara & Co., LTD. / Amuza Inc. | FMM-ST | |
Punching board for rats | O’Hara & Co., LTD. / Amuza Inc. | FMR-ST | |
Treadmill for rats | O’Hara & Co., LTD. / Amuza Inc. | FMR-TM |
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