Open source camera system that images natural habitats as they appear to rodents

During evolution, animals have adapted to the particular demands of their local environment in order to increase their chances of survival and reproduction. This is also true for various aspects of the sensory systems that allow species to perceive their environment. In the case of the visual system, these adaptations have such shaped characteristics as the positioning of the eyes and the relative acuity of different regions of the retina.

However, knowledge of the functional evolution of visual systems in mammals has remained relatively sparse. “Over the past 10 or 15 years, the mouse has become the preferred model for studying visual information processing”, explains Professor Laura Busse of the Department of Biology II of the Ludwig-Maximilians-Universitaet (LMU) in Munich. “This is a somewhat surprising development, given that it was previously thought that these rodents mainly smell the world using their whiskering system and scent.” However, color vision in mammals is known to have an effect on the ability to find food, evade predators, and choose mating partners.

“It occurred to us that we don’t really know how mice visually perceive their natural environment,” says Busse, a member of the Center for Transregional Collaborative Research (CRC) 1233 on “Robust Vision”. Here, the term “robust” refers to the fact that animals (including humans) are able to draw conclusions from limited amounts of visual information, even in constantly changing environments. Busse decided to fill this gap by studying visual input and neural signal processing in mice, “together with Professor Thomas Euler of the University of Tübingen, the coordinating University of CRC.

A camera that captures the view of the mouse

Mice are bichromate, meaning they have two types of cone cells (the photoreceptors responsible for color vision) in their retina. These cells detect electromagnetic radiation in the green and ultraviolet regions of the spectrum, centered at wavelengths of 510 nanometers (nm) and 350 nm, respectively. “We wanted to know what range of color information is available to mice in their natural habitats, and whether the prevalence of these colors can explain the functional characteristics of neural circuits in the mouse retina,” says Busse.

Together, the Munich and Tübingen teams set out to develop a low-cost, open-source camera that, unlike conventional cameras, was specifically designed to cover the spectral regions of green and ultraviolet to which the mouse retina is. sensitive. For ease of use in the field, the handheld camera is equipped with a gimbal, which automatically orients the photo frame, preventing sudden and unintentional perspective changes.

The researchers used this camera to image the environment as it would appear to a mouse, at different times of the day, in fields that showed clear signs of their presence. “We knew that the upper hemisphere of the mouse retina, with which they can see the sky, is particularly sensitive to UV light,” says Busse. “The lower half of the mouse retina, which is normally oriented towards the ground, shows higher sensitivity in the green region. The team confirmed that these two spectral ranges closely match the color statistics of natural environments favored by mouse populations. This adaptation could be the result of evolutionary processes – and for example helping the animal to perceive birds of prey in the sky – and take avoidance measures. Experiments using artificial neural networks that mimic the processing characteristics of cone cells in the mouse retina support this conjecture.