An olfactory virtual reality system for spatial behaviors in mice

Tese de Mestrado Integrado, Engenharia Biomédica e Biofísica (Sinais e Imagens Médicas), 2022, Universidade de Lisboa, Faculdade de CiênciasAnimals have the ability of finding their way in their environments, being able to reliably visit known sources of food or water and return to their burrow or nest. Olfaction plays a major role in the spatial navigation behaviors of animals across phyla, however little is known about how olfactory and spatial information are actually combined in the brain in order to generate those behaviors. When studying spatial navigation in laboratory conditions, scientists typically design mazes where freely-moving rodents are provided with a rule for quickly navigating to rewards distributed in the environment, but investigating how olfactory information is processed in the brain is extraordinarily challenging if one cannot account for the olfactory properties of the environment a freely-moving animal is navigating in. In order to more precisely control the spatio-temporal dynamics of olfactory stimuli in experiments involving freely-moving animals, these typically consist of odorized air flow pulses that are delivered at sparse locations in behavioral arenas, which require expensive instrumentation and increase the complexity in the physical construction of the mazes while also being inherently limited in the locations the stimuli can be provided. Here, we have developed a virtual reality system that allows for the precise control of olfactory stimulus delivery properties in head-fixed navigating mice in both open an closed-loop conditions. By nature, it allows the parameterization of both the visual and olfactory dimensions of the environment, which potentiates the comparison of behavior and neural activity of mice navigating in environments containing different visual and olfactory scenes. In addition, the system is constructed mostly from standard laboratory equipment and draws from open source solutions, promoting its adoptability in different domains of research, and contributing to improve the replicability of experiments across institutions. We validate this olfactory virtual reality system by designing a spatial navigation task where olfactory stimuli are predictive of reward location. Our results confirm the system is able to produce olfactory and visual virtual environments that are controlled by the movement of head-fixed mice in a closed-loop. Finally, to complement the behavioral data, we also present data demonstrating the compatibility of our system with cutting edge neural population recording techniques