A Real-Time Interactive System for Studying Confrontational Pursuit Behavior in Rodents

Predatory pursuit behavior involves various physiological processes, yet lacks suitable research method. This research aims to propose a standardized method to explore neural mechanisms of animal behaviors triggered by sensory stimuli, especially in predator-prey chasing. Technologies like optogenetics, electrophysiology, and brain imaging are commonly used to advance science in this field. Optogenetics enables precise control of neural activity and the electrophysiology records neuronal signals. The main challenges are the uncontrollability of live prey, such as crickets, which makes it difficult to observe and define chase to standardized experiments. Predatory behavior can be divided into four stages, searching, chasing, attacking, and consuming. In recent years, the latter two stages have been widely studied, whereas the searching and chasing behaviors have been rarely involved. This protocol provides flexible and controllable artificial prey for repeated experiments and modeling, maximizes the simulation of natural hunting with real-time interaction and low latency, and offers scalable hardware and software that are cost-effective and easy to use.

[Narrator] To begin, mount a webcam on a crossbar above the entire platform to monitor in real-time the positions of the mouse and robotic bait in the arena below and transmit the images to the computer. Design a large circular arena with an 800-millimeter diameter and 300-millimeter height, consisting of a square acrylic panel at the bottom and an acrylic tube as the border. Place four evenly spaced icons, square, triangle, circle, and cross, on the interior walls of the arena to serve as visual cues. Attach a blue sticker to the surface of the magnet for easy identification and location. Use a round neodymium magnet with food pellets as a robotic bait. Then, mount a two-dimensional slider with an effective travel of 1,000 millimeters under the arena. Install another neodymium magnet on the carrier of the slider to serve as the pulling magnet for remotely moving the robotic bait using magnetic force. Drive the polar magnet using servomotors that are controlled by an STM32 board and a switching circuit. Write a diagram for speed control mode. Set the servomotor to speed direction mode where the high or low signal levels encode forward or reverse direction, and the frequency of the PWM wave output encodes speed. To move the robotic bait to the center of the arena, run the reset program. Isolate the mouse at the edge of the arena using a baffle. After that, set the experiment name and the path of the file. Then, set the moving speed of the robotic bait to 5 centimeters per second in the main program. Click Run and verify in the pop-up video window that the mouse and robotic bait are stably recognized. Remove the baffle and start the timer to observe the predatory behavior of the mouse for 20 minutes. Return the mouse to its cage and allow a 24-hour recovery period with free access to food and water. After each habituation trial, clean the arena thoroughly using 75% alcohol and water. Move the robotic bait to the center of the arena by running the reset program as shown previously, and isolate the mouse with a baffle at the edge of the arena. After setting the experiment name, path of the file, and moving speed of the robotic bait, click Run on the software and observe the video window to ensure stable detection of both the mouse and the robotic bait. Remove the baffle and start the timer. If the mouse captures the robotic bait within 60 seconds, close the main program and allow the mouse to consume all the food pellets before being returned to the cage. Return the mouse to the cage without any reward or punishment if the mouse fails to capture the robotic bait within 60 seconds. The predation tasks were conducted at different speed difficulties, and the results show that the time to first robotic bait capture significantly decreased across habitation trials, indicating rapid learning in mice. Mice had higher capture success at 15 centimeters per second than at 30 centimeters per second, showing speed-dependent difficulty. However, predation time stabilized below 15 seconds after repeated trials regardless of bait speed. Distinct search and pursuit phases were also observed in the mice's movement patterns. Pursuit behavior was reliably induced across bait speeds, shown by reduced distance and increased speed during pursuit. The predation tasks were also conducted with different escape strategies. However, the beta escape strategy did not affect the predation success rates. Predation time decreased and stabilized below 15 seconds with both escape strategies. Mice showed consistent pursuit behavior under both escape strategies.