A novel system for tracking arousal-related dynamics in freely moving animals

Abstract High-speed, high-fidelity physiological readouts are critical to neuroscientists who aim to link these responses to behavioral or neuronal activity. Despite the importance of these measurements, the current “gold-standard” biometric monitoring technology in animal models greatly restricts the scope of experimental implementation. At present, simultaneous tracking of these physiological measurements requires multiple bulky devices that must be attached to the animal and synchronized with neural activity, inducing stress and limiting naturalistic animal behavior. Carolina Instruments’ lightweight, freely moving Biometric Ocular Photometry (BOP) system has the potential to address these challenges by simultaneously measuring multiple biometric readouts in real time with minimal impediment to the animal. Our BOP technology leverages photoplethysmography (PPG) techniques for the simultaneous measurement of pupil size, heart rate, and respiratory rate in mice. Infrared (IR) light emitted from an LED positioned on the head passes through the brain and exits via the pupil, where it is captured by a small sensor placed in front of the eye. IR light signal fluctuations are modulated by pupil size, absorption due to blood oxygenation, and brain movement linked to respiratory activity. The compact and lightweight nature of the LED and sensor enables this noninvasive approach to seamlessly integrate into both head fixed and freely moving mouse experiments. Furthermore, the simultaneous real-time measurement of each signal eliminates the need for complex and error-prone post-processing to synchronize the various signals. The goals of this project are to make improvements to the hardware and data processing to prepare for clinical translation. Aim 1: Optimize the BOP system to maximize testing durability and minimize animal stress. Devices with inadequate form factors can stress animals and limit the duration of experiments. We will address these limitations with hardware adjustments to optimize device size and durability, making the technology suitable for prolonged experiments in freely-moving mice. We will then validate the functionality of the freely-moving device by collecting simultaneous pupil size, heart rate, and respiratory rate measurements, and comparing the results to those from state-of-the-art biometric monitoring tools. Aim 2: Improve the reproducibility of data collection and reporting. In its current state, our technology requires an experienced user to perform surgery and to operate the device. We will implement hardware and software modifications to ensure that surgical device placement and data collection become robust, repeatable, and accessible to new users. A surgical placement tool will facilitate the repeatable placement of our baseplate across animals, and a turn key self-calibration step will ensure that the device is properly operational before starting experiments. Additionally, a signal processing algorithm will provide real-time assessments of data reliability along with all reported data. The completion of this project will lay the foundation for future work refining the device to prepare for large-scale manufacturing, finalizing software infrastructure, and expanding to additional animal models.