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Virtual reality arena for flies. Photo: strawlab.org/freemovr via University of Vienna.

Taking inspiration from Star Trek’s concept of a holodeck, a team of researchers has created an immersive, 3-D virtual reality system that allows animals to move freely and respond to the environment they are in.

The system, called FreemoVR, solves many of the current limitations researchers face when trying to study brain function and behavior.

Current virtual reality techniques can generate a natural-looking environment for lab animals, but they require the animal to be immobile or restrained because the system cannot react or adjust to what the animal is doing. This limitation restricts sensory input and feedback, and ultimately changes neuronal and behavioral responses.

The FreemoVR system, developed through a collaboration of researchers from the University of Freiburg, the Max F Perutz Laboratories, University of Vienna, and other institutions, includes a “behavioral arena” built with walls and floors that are equipped with computer displays. The displays incorporate computer game technology to mimic a specific environment, which enables lab animals to explore the environment at their will while walking, flying, or swimming.

The key advantage of the system is that the animals can move freely and explore the environment from their own perspective without any restrictions. High-speed cameras document the animal’s movements in 3-D and in real-time, enabling the projections on the walls of the arena to be constantly adjusted. This way, researchers can control the animal’s visual experience while maintaining natural feedback from an animal’s senses.

"We wanted to create a holodeck for animals so that they would experience a reactive, immersive environment under computer control so that we could perform experiments that would reveal how they see objects, the environment, and other animals," said Andrew Straw, leader of the development of FreemoVR.

The team validated the VR system’s abilities by testing the reactions of free-moving zebrafish, mice and flies.

In one experiment, the researchers found that mice responded the same way to both a real and virtual maze that had varying elevations. The real maze featured one side that was higher from the ground than the other, and the virtual maze mimicked that aspect of the real maze by giving the illusion of depth and tricking the mice into thinking one end was lower – and therefore safer – than the other end. In both the real and virtual mazes, the mice stayed on the lower side of the platform.

In another test, a tank filled with zebrafish was placed in the circular FreemoVR arena, and a swarm of aliens from the Space Invaders arcade game was projected on the walls. The fish reacted as they would if the creatures were real – and even engaged in behavior to “join” the swarm of aliens.

They also observed that the prospective leader zebrafish minimized the risk of losing followers by balancing his internal preference for a swimming direction with the social responsiveness of subordinate fish.

Although the FreemoVR system is a crucial improvement in the effort to accurately study free-moving animals, it still has some limitations. For example, it doesn’t display images with polarized light. Unlike humans, many other animals can naturally see polarized light and use it to navigate.

Now that the system has been validated, the team hopes to gain insights into the brain function of more complex behaviors, as well as social rules within groups.

"I am particularly excited about the possibility to mimic more complex, naturalistic environments and to test more advanced brain functions in medaka and zebrafish. It will help us to better understand brain functions and to what extent we can use these diurnal vertebrates as models for neuropsychological malfunctions,” said MFPL scientist Kristin Tessmar-Raible, who led most of the fish work.

The team’s findings have been published in Nature Methods.

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