This maze was first described in the literature by Sato et al (2017) for learning and memory. The device comes with five vertical and five horizontal corridors that allows for a flexible construction of routes. Similar to the Hebb Williams maze, successively more difficult modular tests are performed on the rodent to create environments that challenge spatial learning memory. The device from MazeEngineers is available for both mice and rats.

The Object Space Task is a multi-trial behavioral assay used to assess and track memory accumulation in the rodents. Similar to the Open-Field test, the task relies on the subject’s innate exploratory drive and curiosity of novelty. The task makes use of objects placed within the arena that subject is either familiarized with or not. Unlike other memory assays such as the Morris Water Maze or the Radial Arm Maze, the Object Space Task does not use aversive motivations or other strong motivations. By using an object-recognition paradigm the effects of motivation, emotion and the neuromodulatory system are minimized on the memory processes required to perform the task. Thus, performances in the Object Space Task allow assessment of memory and learning comparable to neutral paradigms used in human trials.

The chief advantage of the Object Space Task lies in its simplicity and the feasibility of multiple uses. It also allows assessment of behavioral as well as physiological measures. Most importantly, the task requires minimal training of the subject. The Object Space Task consists of a square arena with high walls that prevent the subject from leaving the arena. The task is performed using pairs of objects placed at specific spatial locations within a trial. Investigation of memory and learning involves different configurations of object location and object novelty. The multi-trial and multi-configurations of the apparatus enables differentiation between whether the brain retains the detail of a specific event (episodic memory) or represents the overall knowledge extracted through multiple learning experiences (semantic memory).

Other apparatuses and tasks used in the assessment of memory and learning include the Hebb Williams Maze, the Lashley III, the Barnes Maze, and the Y-Maze.

Clean the Object Space Task apparatus and the objects used in the trials prior to being used to eliminate the influence of any lingering cues on the task performance. Appropriately illuminate the arena. A tracking and video system such as the Noldus EthoVision XT can be used to assist with the task observation. The Object Space Task apparatus can be used with different investigatory protocols.

Pretraining

Improper handling of the subjects can affect task performances. Thus, allow the subject to climb by itself onto the experimenter’s hand. Begin the first habituation process by allowing a group of subjects (preferably cage mates) to explore the arena for 30 minutes. Follow this by two 10 minutes sessions of individual exploration of the arena. Remove the subject from the arena once it has familiarized itself with the arena and fix two objects within the arena. Allow the subjects to individually explore the maze and objects in final two 10 minutes sessions. Repeat sessions for at least 5 days.

Object Space Memory Accumulation Task

The memory accumulation task consists of three experimental conditions: stable, overlapping and random, wherein different combinations of spatial locations and visual cues are used. Perform sample trials (3 to 5 trials per day) with groups of subjects for each condition and allow them to explore the pair of objects for 5 minutes. Each trial should be separated by 30 to 50 minutes inter-trial interval. Repeat sessions over the course of 4 days. Perform the final test trial (10 minutes) after 24 hours of the last sample trial.

Stable Condition

Place the object pair in the same location for all the sample trials. Following the sample trials, perform the test trial with one of the objects in the pair moved to a new location.

Overlapping Condition

Maintain one object in the same spatial location throughout the sample and the test trials. Move the second object between the remaining three locations in the arena throughout the sample trials. In the test trial, maintain the same spatial location of the object pair as the last sample trial.

Random Condition

Change the spatial location of each object throughout all the sample and the test trials.

Investigation of memory accumulation in rats and mice

Male C57Bl6/J mice (7 to 8 weeks old) and Lister Hooded rats (12 weeks old) were evaluated for their ability to learn and remember the spatial locations of objects in the Object Space Task. Performances of C57Bl6/J mice were compared between a 3 sample trials/day and 5 sample trials/day training schedule. On comparison of the performances of the mice in the two schedules, it was observed that extensive training (5 sample trials/day) allowed a more effective measure of memory and learning. Lister Hooded rats, on the other hand, were trained for 5 sample trials in one day before being evaluated in the final test. Overall analysis of both mice and rat performances showed that cumulative memory was evident in the overlapping condition (positive discrimination index). For stable condition task, performance only increased in the test trial, while in the random condition trial subjects showed no significant preferences. (Genzel et al., 2015)

Before beginning the sessions, clean the apparatus thoroughly to avoid the unnecessary influence of any lingering cues. Ensure the apparatus is well-lit. Tracking and video recording can be performed using software such as the Noldus Ethovision XT.

Pre-training

Habituate the subjects to the maze over the course of 2 days. Allow 10 minutes’ exploratory sessions per day to familiarize the subject with the maze set-up. Unfamiliar conspecifics used for the experiment may also require habituation training to the wire cages.

Social interaction trials

Place the unfamiliar conspecific (preferably same sex as the test subject) in one of the wire cages of the goal arms. In the other wire cage place a dummy object such as a small plastic block. Place the subject in the start arm and initiate the social interaction trial. The trial should last at least 5 minutes. On completion of the task, remove the subject and the conspecific from the maze and place them in their home cages.

Evaluation of transgenerational effects of prenatal immune activation

using C57Bl6/N mice generated three generations of polyI:C or control offspring. On gestation day 9, pregnant dams either received a single injection of poly(I:C) (5 mg/kg; potassium salt) or vehicle (sterile pyrogen-free 0.9% NaCl). The offspring of these dams (F1) were weaned and sexed on postnatal day 21. Breeding pairs were selected from F1 offspring on postnatal day 70 onwards to produce subsequent generations. The offspring not chosen for breeding were used in behavioral testing. This process was done until F2, and F3 generations were obtained. Subjects of each generation were tested on the Social Y-Maze. Result analysis revealed that poly(I:C)-exposed F1 offspring showed impairment of social interactions. A similar observation was made in the F2 generation.

Investigation of Vitamin D treatment in preventing autism-related phenotypes

Vuillermot used C57BL6/N offspring of pregnant dams divided into 4 treatment groups. Groups consisted of pregnant females that were first injected subcutaneously with 1,25OHD (Vit_D) or vehicle (VEH) followed immediately by intravenous injection of either poly(I:C) (POL) or saline solution (CON) on gestation day 9. This led to the following 4 combinations: CON/VEH, CON/VIT_D, POL/VEH and POL/VIT_D. Subjects were individually tested in the Social Y-Maze task. Results suggested a significant interaction between MIA and Vit_D. The percentage time spent with the unfamiliar conspecific significantly decreased in POL/VEH group in comparison to CON/VEH group.

The following observations can be made during the Object Space Task:

• Total exploration time
• Time spent with each object
• Time spent in each spatial location
• Path traveled
• Distance covered
• Discrimination Index

The Discrimination Index is calculated as the difference in time exploring the novel object location and stable location divided by the total exploration time. Discrimination Index scores range between -1 (preference for the stable location) to +1 (preference for the moving object location) with the score 0 indicating no preference for either object location.

Strengths

The simplicity of the Object Space Task apparatus allows experimenters the scope to apply different protocols, environmental contexts, and objects’ spatial configurations. The task does not rely on aversive motivations (such as fear of drowning or shocks) or other strong motivations (such as hunger) as seen with other memory assays. The memory and learning task makes use of an object-recognition paradigm that exploits the subject’s innate exploratory drive for novelty. Thus, the performance is not affected by motivation, emotion or the neuromodulatory system and is less stressful in comparison to other assays. The multi-trial and multi-configuration nature allow differentiation between episodic and semantic memory.

Limitations

Since the Object Space Task relies on the subject’s exploratory drive, it is important that it is maintained throughout the training. Handling of the subjects is also a critical factor that can influence the task performance. Inappropriate handling, such as lifting the animal by its tail, may subject it to unnecessary stress which in turn will affect the task performance. Most rodents have a preference for dark closed spaces. Therefore, it is important that the lighting conditions are not aversive to the subjects. The task requires good locomotion and vision; hence it cannot be effectively applied in animals with either motor or vision deficits. Care must be taken to ensure the subjects are not disturbed during the trials. Factors such as age, strain, and gender can affect performances. Presence of unnecessary visual, olfactory or auditory stimuli will lead to erroneous results.

• The Object Space Task is a multi-trial behavioral assay for assessment of memory and learning.
• The task relies on the animal’s innate drive to explore novelty rather than on aversive or strong motivations. This minimizes the effects of motivation, emotion and the neuromodulatory system on the task performance.
• The object-recognition paradigm used in the Object Space Task allows comparable performances to neutral paradigms used in human research.
• The simple design of the apparatus permits the use of different protocols, objects’ spatial configurations, and environmental contexts.
• Subjects with poor or deficient vision or motor skills may not be suitable for evaluation in the Object Space Task.
• Improper handling of the subject may introduce effects of stress on the task performances.