Laboratory mice will now wear virtual reality on custom-made headsets as scientists seek breakthroughs in human brain research.
By studying the way mouse brains register their environment, scientists can gain a better understanding of how people's brains map the physical spaces around them, opening the door to understanding and treating movement and balance disorders.
To get good data about how a mouse's brain works, scientists need to properly simulate the real world
And a surprisingly common area of research in mouse behavior is the way they process top-down threats.
Think of eagles or hawks, birds of prey that see a mouse as a perfect piece of food.
Now, a team of scientists from Northwestern University has developed a way to make this experience feel much more realistic for mice.
A new device can place mice in an immersive simulated environment that covers their entire field of view, thanks to a headset that places a screen over each eye.
And the scientists behind it say it's simpler and cheaper than traditional setups, making science more accessible.
Scientists already have ways to immerse mice in visual environments, but they don't cover a mouse's entire field of view, leaving gaps at the edges where they can see the lab or even the scientists out of the corner of their eyes.
“We've been using VR systems for mice for the past 15 years,” said senior author Daniel Dombeck, a professor of neurobiology at Northwestern.
“Until now, laboratories use large computer or projection screens to surround an animal,” he said.
The new device vastly improves on existing options, the developers claim
Usually this means placing mice in front of a 5-panel screen.
'For people this is the same as watching TV in your living room. You still see your couch and your walls. There are cues around you that tell you that you are not in the scene. Now think about putting on a pair of VR glasses, like the Oculus Rift, that take up your entire vision. You see nothing but the projected scene, and a different scene is projected into each eye to create depth information. That was missing in mice.'
In this new one, called iMRSIV (Miniature Rodent Stereo Illumination VR), each eye is equipped with video that fills approximately 180 degrees of vision.
The research appeared in the journal Neuron on Friday.
A mouse can see about 140 degrees around them with each eye, and their two eyes overlap by 40 degrees, giving them binocular vision within that range.
So if scientists want to give them a realistic experience, they can't just project 180 degrees to each eye and call it a day.
An interior view of the iMRSIV headset. Each lens sends an image from a small screen to the mouse's eye
The two images must share that 40 degree overlap, otherwise the mouse will know something is wrong.
They built each half of the entire structure with a small OLED screen, a custom concave lens and a 3D printed frame.
Then they tested it.
Scientists placed each mouse in a device that held the head in place while the feet remained free on a treadmill – think the ultimate VR gaming setup.
Connected to this device, mice were trained to run along a virtual track.
On average, they reached “expert level” after about six days of training, the study authors wrote.
They then trained them to see a looming object above their heads.
To the immersive environment of the simulated track, they added a section where the roof suddenly disappears and there is an open space above.
As small prey animals, mice find this situation uniquely frightening.
Compared to mice looking at a traditional 5-panel screen, the mouse with a VR headset froze much more reliably – a sign of fear or anxiety.
The animals looking at a traditional screen saw only the shadow of the object, making it relatively ineffective, they wrote.
Then the team pointed a two-photon microscope at the mice's heads to spy on neurons in their brains.
They looked specifically at place cells, the neurons associated with spatial memory and navigation in physical space.
They found that the brain characteristics of the VR-wearing mice were similar to those of mice that walked freely, supporting the idea that this system can accurately simulate physical space.
Their brain results were exploratory, as the study was intended more to outline and validate the development of the device, rather than to conduct specific experiments.
“In the future, we would like to look at situations where the mouse is not the prey, but the predator,” John Issa, a postdoctoral researcher in Dombeck's lab and co-first author of the study, said in a statement.
'For example, we can watch brain activity as it chases a fly. That activity involves a lot of depth perception and estimating distances. These are things we can start recording.'
However, the simplicity of installation is an advantage.
“Traditional VR systems are quite complicated,” Dombeck said.
'They're expensive and they're big. They require a large laboratory with plenty of space. And besides, if it takes a long time to train a mouse to perform a task, that limits the number of experiments you can do. We are still working on improvements, but our glasses are small, relatively cheap and also quite easy to use. This could make VR technology more available to other labs.”