Scientists have created a virtual reality system that allows fruit flies to fly around a virtual pillar, and zebrafish to swim with aliens from the video game Space Invaders. The goal is not to give animals a good time, but for scientists to study how mice, flies, and fish respond to the VR worlds in real time. It’s basically a new tool to study animal behavior in the lab.

The VR system, called FreemoVR, pretty much resembles a holodeck from the TV show Star Trek. It’s an arena surrounded by computer screens that immerses the animals in a virtual world. Researchers tested the system on mice, fruit flies, and zebrafish, and found that the animals reacted to the virtual objects and environments as they would to real ones. The findings were published this week in the journal Nature Methods.

When studying animals in the lab, it’s hard to re-create natural environments, where animals can move freely. VR has been used before, but often it involves blocking the animal in a harness or gluing it down, so that the virtual images don’t have to adjust to what the animal is actually doing, says study co-author Andrew Straw, who studies neural circuits and behavior at the University of Freiburg, in Germany.

The FreemoVR is different because it allows the animal to move freely — or at least as far and wide as the VR arena goes. Multiple high-speed cameras also track the animal in 3D in real time, so that the video on the walls can be adjusted constantly to respond to the animal’s movements. “I really wanted to be able to put animals in video games essentially,” Straw tells The Verge. And he kind of did that.

In one of the experiments, the researchers projected a swarm of aliens from the video game Space Invaders all around the walls of a fishbowl. (The images were constantly updated, their position shifted in real time, so they looked 3D to the zebrafish swimming inside the bowl.) The zebrafish responded to the aliens as if they were real fish, swimming to the center of the bowl as if swarming with them. “It was really like a hybrid biological computer swarm,” Straw says. In another experiment, fruit flies flew around a virtual black cylinder just as they flew around a real cylinder placed in the arena.

In yet another experiment, mice were placed on a round track located on a large TV screen. Because of different checkered patterns shown on the screen, half of the track looked more elevated than the other. The mice avoided the track that looked suspended higher up, just like they did when the track was actually at a greater height.

The setup isn’t perfect. Because FreemoVR uses computer screens and projectors made for humans, it doesn’t show images that have polarized light, for instance. Unlike people, many animals can see polarized light and use it as a sort of compass to know where to go, Straw says. So when studying how animals move in a VR arena, it’s never going to be exactly like studying how animals move in real life. Still, it’s as close to it as we can get — at least for now.

The technology can be used to help us better understand how animals build maps of the world, how they navigate, and how they interact with other animals. For his part, Straw wants to use the technology to study how fruit flies react to virtual but seemingly natural environments in the lab, and then understand the role of specific neurons in particular types of behaviors.

And you never know, you might have to fly some animals around with space invaders to figure that out.