The traditional T-maze can be used to test both delay-and effort-based decision-making. In the current work, we invented a T-maze apparatus with automated food delivery, door management, and arm choice recordings. Our protocol here can dramatically save researchers time and labor while analyzing the decision-making ability of rodents.
This protocol can help to answer the key questions in decision-making fields, such as what are the key neural circuits and molecules underlying decision-making procedure, and what are the neuropathological causes underlying decision-making deficits in psychiatric diseases? The implication of this protocol extend toward therapy of neuropsychiatry disease because many patients demonstrate difficulties or deficit in decision-making. Habituate mice to the maze for 10 minutes per day and totally for five days.
Keep all the maze doors open during habituation. On day one, scatter the food pellets throughout the maze. Then, place the mice in the start box of the T-maze in groups of four, and allow the mice to explore the maze for 10 minutes.
On days two and three, scatter the pellets along the two goal arms. Allow the mice to explore the maze for 10 minutes. Finally, on days four and five of habituation, put the pellets only very close to and at the food dispensers at the two goal boxes.
Allow the mice to explore the maze for 10 minutes. For the forced arm entry phase, begin by setting up the control software parameters. Set the duration to 900 seconds.
Set the default start delay time to three seconds, the pellet number to one for LRA and four for HRA, and set the delay time to zero seconds. Register the ID of each individual mouse to the software and the location of the HRA for each individual mouse, either on the left side or the right side. Then, enter the experiment interface window, place the mouse in the start box, and initiate the training by pressing the start button on the remote control.
Note during each trial, only the doors leading to one arm will be open, while the doors on the opposite arm will not be open, and the doors automatically open or close according to the position of the animal. Here, the mouse was forced to enter the left side HRA in the first trial and eat the four pellets and to enter the right side arm in the second trial to eat the one pellet. This phase allows the mouse to learn the position of HRA and LRA.
For the free arm entry phase, set the parameters by using the same method as used in the forced entry phase. Place the mouse in the start box, press the start button, then allow the mouse to freely choose one arm, either HRA or LRA. Begin by setting the delay time of the HRA to five seconds, 10 seconds, and 15 seconds on day one, day two, and day three, respectively.
Set the phase number. Set all other parameters in the same manner as the forced arm entry phase. Allow the mouse to freely choose one arm, either HRA or LRA.
In the two trials shown here, the mouse chose the LRA in the first trial and chose the HRA in the second trial. Next, for the effort-based decision-making test, introduce the barrier to the HRA. Allow the mice to freely choose one arm, either HRA or LRA.
Here, the mouse chose to climb the barrier to get a higher reward. After the experiment is complete, obtain data and results from the control software. Look for all experimental data in the data folder.
Finally, check items in the result folder, duration, trial number, HRA choice number, LRA choice number, HRA choice percentage, LRA choice percentage, total moving distance, and total junction time under each animal ID.The results shown here display the differences between delay-and effort-based decision-making ability between medial habenular ablated mice with their littermates, wild-type control mice. For the delay-based decision-making test, the main effect of genotype was not significant when the delay time was five seconds. However, when the delay time was elongated to 10 seconds and 15 seconds, the medial habenular ablated mice demonstrated a significant reduction in the percentage of HRA visits compared to CT mice.
Lastly, in the effort-based decision-making test, the percentage of HRA visits were significantly decreased in the medial habenular ablated mice when a barrier was placed in the HRA, regardless of the left/right localization of the HRA. While attempting this procedure, it's important to remember food restriction should be done throughout all the training procedures to ensure the motivation of the rodent to perform the task. In addition, remember to use the tiny size 10-milligram pellets and use silica gel in the food dispensers to keep the pellet dry.
Following this procedure, other methods like in vivo electrode recording, fiber optic imaging, optogenetics manipulation, and microdialysis can be performed in order to answer additional questions, for example, the dynamic changes of excitability of specific cell populations during delay and effort discounting and dynamic changes of neuropeptides, neurotransmitters, and hormones during decision-making. In one word, the current setup and the protocol that we developed allow researchers to efficiently analyze decision-making of rodents, with full automation, standardization, and high-throughput capacity. We believe that our invention can help to elucidate the mechanism underlying decision-making for both physiological and pathological conditions.
