The Food Carrying Apparatus is used to study navigational behavior in rodents. It is an adaptation of the food carrying paradigm used by Whishaw, Coles, and Bellerive (1995) to evaluate head direction cell activity in rodents. The Food Carrying Apparatus consists of an open field (see also Open Field Apparatus), wherein the subjects explore the cups in the arena to reach a food reward and exit from the correct refuge. Subject’s navigation in the apparatus can be based on self-movement cues and their ability to learn the correct path. Subjects that exhibit impairments in navigation, piloting behavior, and spatial memory tend to spend more time within the correct refuge and display a decreased proclivity to carrying the food back to the refuge from the open arena.

The Food Carrying Apparatus is a circular arena that is surrounded by a high wall equipped with a series of eight doorways. Among the eight doorways, only one door leads to a refuge while others are false refuges. The open arena is sectioned into a fixed central platform around which the outer arena can be rotated. The floor of the arena is equipped with cups which can be baited with food rewards such as sugar pellets. The Food Carrying Apparatus can be used and adapted for different investigations and tasks such as food handling behavior, spatial learning and memory, and predation risk or odor test (see also Fear conditioning chamber and Predator Odor Exposure Test).

Other apparatuses also used to investigate anxiety, navigational behaviors, spatial memory, and learning include the Elevated Plus Maze, the Light-Dark Box, and the Morris water maze.

The Food Carrying Apparatus is an open field circular arena of 180 cm diameter, equipped with 16 symmetrically placed food cups on the surface. It contains a fixed central elevated platform of 1 cm thickness and 53.3 cm diameter, which is slightly raised compared to the outer field. The entire field is supported by four rolling casters and is mounted on a central bearing that allows the field to be rotated around the central platform. The field is surrounded by a high wall of 38 cm containing eight uniformly distributed doorways of 13 cm width. Each doorway is covered with identical black curtains, parted in the middle to allow the subject to go through. The doorways lead to 7 false refuges with barriers and a single correct refuge. The correct refuge measure 13 cm in width, 40 cm in length and 30.5 cm in height and serves as a comfortable shelter for the subject to consume the food.

Ensure that the central platform is cleaned with ethanol prior to testing to remove any lingering odors from previous subjects and food. Appropriately illuminate the apparatus. An external video tracking software such as the Noldus EthoVision XT can be used to assist with recording and scoring of the navigational behavior of the subjects.

In order to eliminate any external visual cue, it is recommended that the apparatus is surrounded by thick black curtains.

Habituation and Pre-training

Prior to the experiment, bait the food cups with pellets, and place the subject in the correct refuge. Allow the subject to forage for the pellets. Once it finds the pellet, observe its proclivity to return to the correct refuge, and eat the food reward. If the subject tries to eat a pellet in the open field or tries to search for another pellet during the return path to the refuge, make a startling noise, or take the pellet away. Allow animals to retrieve and eat only four pellets per day. Reduce the number of baited food cups as the subject becomes more proficient in the task. Perform the pre-training until the subject completes four successive trials.

Food Carrying Apparatus task

Place visual cues (if any) in and around the apparatus. Place the subject in the correct refuge for a few minutes. Place a food reward randomly in one of the four cups located on the central platform. Allow the subject to explore the central open field platform and forage for the food pellets. Perform 12 food carrying trials in 3 consecutive days (4 trials per day). Initially, perform the food carrying trials by turning off the lights to prevent the utilization of visual cues as a source of guidance. Do not change the position of the refuge throughout the trials.

Rotation probe trial

For the rotation probe trial, place the subject in the refuge again after a few proceedings of the Food Carrying Apparatus task. Rotate the central platform of the Food Carrying Apparatus in either clockwise or anti-clockwise direction. After a few minutes of acclimation, allow the subject to explore the open field, and observe their performance. If the subject returns to the correct refuge, score the trial correct. Terminate the task if the subject shows resistive behavior in the apparatus.

Effect of lesions of the interpeduncular nucleus on landmark navigation and path integration in rodents

Clark and Taube (2009) evaluated the role of the interpeduncular nucleus (IPN) in rodent navigation using 19 female Long-Evans rats. Animals were divided into IPN lesioned group and sham-operated group and evaluated on the Food Carrying Apparatus and the Morris Water Maze. The lights-off trials in a Food Carrying Paradigm identified that both sham and IPN-lesioned rats manifest a similar circuitous pattern while finding food and returning to the correct refuge. The search time of both sham and IPN- lesioned rats were also similar; however, the accuracy of returns to the refuge varied across the groups. The IPN-lesioned rats showed less accurate, less directed return path and took longer time to locate the refuge, unlike the sham-lesioned rats. In the presence of visual cues (lights-on trials), the subjects used a landmark navigation strategy while finding the food and locating the correct refuge. Assessment of beacon navigation abilities of the subjects revealed both groups accurately navigating towards the cued platform in the Morris Water Maze task. The IPN-lesioned rats exhibited overall higher swim latencies compared to the control group. It was concluded that IPN-lesions are responsible for deficits in both landmark navigation and path integration capabilities of the subjects. However, these lesions do not necessarily affect the beacon navigation.

Role of Anterodorsal Thalamus and Dorsal Tegmental Nucleus in Navigation and path integration in rats

Frohardt, Bassett, and Taube’s (2006) investigated the potential role of two regions of the head direction (HD) cell circuits: the anterodorsal thalamic nucleus (ADN) and the dorsal tegmental nucleus (DTN) in navigation in rats. Naïve, adult female Long Evans rats were trained on the Food Carrying Apparatus with and without blindfolds prior to undergoing either AND, DTN or sham lesions. The ADN-lesioned rats committed more errors than the control group in the food carrying task. Further, their performance was not satisfactory in the blindfolded version of the task in contrary to the visual version. Additionally, the ADN-lesioned rats also showed a significant difference in both initial and final headings during the task compared to the control group. These results suggested that ADN and HD cells play a vital role in resolving the path integration and piloting in rats. The performance of DTN-lesioned rats was poor in the blindfolded condition compared with the control groups. Overall, the ADN-lesioned rats showed mild impairment in both versions of the food carrying task. However, the DTN-lesioned rats showed severe impairment with reduced head accuracy in the blindfolded and visual versions of the task. It was concluded that both the DTN and ADN contribute to navigation based on path integration and spatial behavior, but DTN has a considerably greater effect on accurate navigation in rats on the basis of path integration or visual signals.

Role of Head Direction Signal during navigation as a neural compass

Butler, Smith, van der Meer, and Taube (2017)  evaluated the role of head direction signal in rodents. The dorsal tegmental nucleus (DTN) of the subjects was infected with a viral infection to produce instability in the head direction signal. The subjects with flux in head direction signal made more homing errors in the Food Carrying Apparatus under dark conditions. However, under standard conditions, the HD cells remained stable, and subjects made less homing errors. The animal’s locomotor behavior was not affected by the optogenetic induction of HD cell instability. The total number of head turns, total linear distance traveled, and the numbers of head rotations were not affected at all.  The directional homing errors and the distance traveled while attempting to return to the refuge by the animals under the dark condition in the presence of laser increased significantly. It was concluded that the optogenetic manipulation of the NPH neurons linked with HD cells results in the instability in downstream HD cells in dark conditions. Finally, the animal’s directional homing behavior depends upon the radial asymmetry of the HD signal, which confirms that the HD cells act like a neural compass in navigation in rodents.

Response time and frequencies of following behavioral measures can be evaluated using Food Carrying Apparatus

• Searches: The moment the rat left the refuge to the point at which the rat finds and picks up the food pellet
• Return segment: The point in which the subject picks up the food pellet and carries it back to the correct refuge
• Initial heading angles: The angle between the refuge and the directional heading of the subject whilst the subject left the food pellet
• Final heading angle: The angle between the refuge and the subject’s directional heading when it approached the refuge and crossed the implicit finish line
• Retrieval trial: The exit from the refuge and return with a food pellet
• Correct choice: Finding a food pellet and returning to the starting doorway without stopping at any other doorway
• Incorrect choice: Finding a food pellet but stopping at one of the other potential exits before returning to the exit from which departure began.
• First choice: The first doorway visited after finding a food pellet
• Second choice: The second doorway visited, given that the first choice was incorrect. The second choice could also include a preservative comeback to the first choice.

Strengths

The Food Carrying Apparatus task uses a simple design to identify large scale differences in navigational activities of brain-lesioned rats and many types of disease models. Its simple design provides an easy option for researchers who do not have access to more complex operant conditioning apparatuses (see also operant chambers) to conduct decision-making tasks. Due to its compact design, the apparatus can be set up almost anywhere and can be adapted for investigation of effects of aging on navigational behavior and spatial memory in rodents.  The Food Carrying Apparatus task is useful in evaluations of deficits in brain functioning as a result of brain injury and repeated drug testing. The Food Carrying Apparatus generally does not produce anxiety in subjects due to the absence of significant stressors allowing better observations of the results and enabling the subject to explore the apparatus arena. The Food Carrying Apparatus does not require food and water restrictions and exposure to aversive stimuli.

Limitations

Factors such as age, weight, sex, visual cues, and light intensity used can affect task performance. Additionally, the use of auditory cues could also alter results by impacting the behavior of the subject. The apparatus requires several days and rounds of habituation, training, and testing session, which can prolong the time period required to obtain the data. Over handling is another factor which could affect the behavior of the subject.

• The Food Carrying Apparatus is used to study navigational behavior in rodents.
• The Food Carrying Apparatus is a circular open field platform with food cups on the floor of the arena.
• The open field is surrounded by a wall equipped with eight doorways that lead to 7 false refuges and 1 correct refuge.
• The Food Carrying Apparatus is a useful paradigm to evaluate associative learning, exploratory behavior, decision making, foraging behavior, spontaneous and forced alternation tasks, and allocentric learning in rodents.

1. Frohardt, R. J., Bassett, J. P., & Taube, J. S. (2006). Path integration and lesions within the head direction cell circuit: comparison between the roles of the anterodorsal thalamus and dorsal tegmental nucleus. Behavioral Neuroscience, 120(1), 135.
2. Whishaw, I. Q., Coles, B. L., & Bellerive, C. H. (1995). Food carrying: a new method for naturalistic studies of spontaneous and forced alternation. Journal of neuroscience methods, 61(1-2), 139-143.
3. Butler, W. N., Smith, K. S., van der Meer, M. A., & Taube, J. S. (2017). The head-direction signal plays a functional role as a neural compass during navigation. Current Biology, 27(9), 1259-1267.
4. Clark, B. J., & Taube, J. S. (2009). Deficits in landmark navigation and path integration after lesions of the interpeduncular nucleus. Behavioral Neuroscience, 123(3), 490.