Rodent Arena Tracker (RAT): a machine vision rodent tracking camera and closed loop control system.

Abstract Video tracking is an essential tool in rodent research. Here, we demonstrate a machine vision rodent tracking camera based on a low-cost, open-source, machine vision camera, the OpenMV Cam M7. We call our device the Rodent Arena Tracker (RAT), and it is a pocket-sized machine vision-based position tracker. The RAT does not require a tethered computer to operate and costs about $120 per device to build. These features make the RAT scalable to large installations and accessible to research institutions and educational settings where budgets may be limited. The RAT processes incoming video in real-time at 15Hz and saves X and Y positional information to an onboard microSD card. The RAT also provides a programmable multi-function input/output pin that can be used for controlling other equipment, transmitting tracking information in real time, or receiving data from other devices. Finally, the RAT includes a real-time clock (RTC) for accurate time stamping of data files. Real-time image processing averts the need to save video, greatly reducing storage, data handling, and communication requirements. To demonstrate the capabilities of the RAT, we performed three validation studies: 1) a 4-day experiment measuring circadian activity patterns; 2) logging of mouse positional information alongside status information from a pellet dispensing device; and 3) control of an optogenetic stimulation system for a real-time place preference (RTPP) brain stimulation reinforcement study. Our design files, build instructions, and code for the RAT implementation are open source and freely available online to facilitate dissemination and further development of the RAT. Significance statement Video tracking is a critical tool in behavioral research. Here, we present an open source machine vision tracking device called the Rodent Arena Tracker (RAT). The main advance of our device over what has been previously done with rodent video tracking is that our solution is small and battery powered, vs. a tethered computer running a software package. This small form factor (about the size of a point-and-shoot camera) can enable new uses for video tracking, including in places where traditional video tracking solutions would be cumbersome or not possible.