12 Dec 2023
Northwestern University platform provides full-field stereo vision as alternative to projection screens.
Traditional methods have included surrounding mice with computer screens or projections, but as virtual reality (VR) goggles and headsets for humans have become more compact and effective, the question of whether mice could wear them too has been a topic of research.
To date most murine headsets have not fully covered the visual field of the animal, damaging the illusion of reality and interfering with the experiments. But a project at Northwestern University has now developed full field-of-view VR goggles for tethered mice that should assist a range of behavioral studies.
As published in Neuron, the platform's improved visual coverage allows the mice to experience a more convincing illusion of overhead threat, such as from looming birds of prey.
"For the past 15 years we have been using VR systems for mice with big computer or projection screens to surround an animal, but that is like watching a TV in your living room with cues around you telling you that you aren't inside the scene," said Northwestern’s Daniel Dombeck.
"Now think about putting on VR goggles that take up your full vision, so you don’t see anything but the projected scene and a different scene is projected into each eye to create depth information. That has been missing for mice."
Northwestern designed a platform named iMRSIV, or Miniature Rodent Stereo Illumination VR, in which each mouse eye is presented with 180-degrees field of view using a single screen and a single lens per eye. This is not possible with a conventional convex lens, so the project designed a customized positive meniscus or convex-concave lens, and paired it with a small curved OLED illumination display of 400 x 400 pixels. Images were projected at 60 hertz.
Natural response from a convincing environment
Unlike VR goggles for a human, the iMRSIV system does not wrap around the mouse’s head. Instead the goggles are attached to the experimental setup and closely perch directly in front of the mouse’s face, according to the project. Because the mouse runs in place on a treadmill, the goggles still cover the mouse's field of view.
Since the design of the iMRSIV device allows access to the overhead area of a subject mice, the Northwestern team was able to carry out two-photon imaging of neural activity while the screens provided visual stimuli to the animal. Changes of environment and the impression of a looming threat were supplied through the VR display, with brain activity mapped as the animal decided whether to freeze or flee.
The tests showed that mice with the iMRSIV goggles learned more quickly than animals experiencing similar training paradigms with conventional equipment. This could be the result of the animal experiencing a more convincing environment and engaging with it in a natural way.
Northwestern plans to improve its platform through higher-resolution screens and perhaps the incorporation of olfactory, auditory and tactile sensations for the mouse. Ultimately a version for freely moving mice based on similar principles might be possible.
"Traditional VR systems are pretty complicated," Dombeck said. “They're expensive, they're big, they require a big lab with a lot of space, and if it takes a long time to train a mouse to do a task, that limits how many experiments you can do. Our goggles are small, relatively cheap and pretty user friendly as well. This could make VR technology more available to other labs."