Rats have an imagination, too, researchers show with brain implants

Our minds have a weird and wondrous way of transporting us to other places and times. You might find yourself, for instance, immersed in the vivid world of a novel, or reminiscing about a potluck with close friends.

These reveries can feel magical, but they’re the result of complex electric signals zipping through the brain. Now a new study shows we’re not the only ones with an imagination.

Scientists found that rats could think of objects and places that were not directly in front of them, a key requirement for remembering the past and imagining the future. The findings, published on Thursday in the journal Science, were based on cutting-edge experiments that blended virtual reality with brain-computer interfaces, implanted devices that eavesdrop on the brain’s electrical signals. Researchers say that what they’ve learned could one day be used to develop prosthetic devices that help paralyzed humans move about.

“This study gives us a hook into the critical element that underlies human imagination in general,” said Albert Lee, a neurologist at Beth Israel Deaconess Medical Center and the study’s senior author.

Imagining isn’t just fun; it’s an important part of how we make complex and risky decisions, such as thinking through whether to quit a job and move to a different city. Visualizing and playing scenarios out in your head is helpful, Lee noted. And our species has been doing that throughout history. Our ancestors, for instance, had to consider whether to form alliances with neighboring tribes.

In the recent study, conducted while Lee and colleagues were at the Howard Hughes Medical Institute’s Janelia Research Campus, researchers explored the precise neurological signals behind imagination. Researchers implanted electrodes into the brains of adult rats. Doing so allowed them to detect electrical activity from the hippocampus, an area of the brain that plays an important role in learning and memory. Previous research had shown that people with injuries to this part of the brain struggle to imagine future scenarios.

The authors then used virtual reality to plunge the rodents into a 3D world, which they could navigate by walking in any direction along a spherical treadmill. Any time the animals approached a spiral pillar in that world, they were rewarded with a few sips of water.

Researchers then used software to link patterns of electrical signals to specific areas within the virtual environment. That was key for the next experiment. The scientists disconnected the treadmill and instead based each rat’s location within the virtual world on the signals from its hippocampus. To earn their reward, the animals would now have to imagine moving toward the spiral pillar.

That’s exactly what they did in a task that researchers dubbed Jumper, a reference to a 2008 sci-film starring Hayden Christensen, whose character can teleport to any place he can imagine.

In another experiment, the rats could imagine moving an object toward a goal post. In this task, the animals’ location was kept constant, but their thoughts were translated into the location of a floating rectangular box. When the object got close enough to a goal post, the animals were rewarded with a drink, and if the object stayed there, the reward continued.

That test, named Jedi in an ode to “Star Wars,” showed that rats could deliberately imagine keeping the object by the goal area for several seconds, which the authors say is similar to how long we typically relive the past or imagine new scenarios.

In an accompanying commentary in Science, Michael Coulter, a postdoctoral researcher at the University of California, San Francisco, noted that it is likely the authors’ findings apply to the real world given past research showing that the activity of the hippocampus is similar in both real and virtual environments. And in an email to STAT, he described the study as pushing the boundaries of brain-computer interface research.

“This study provides new evidence that [brain-computer interfaces] can be applied to more cognitive tasks, such as mental navigation,” wrote Coulter, who was not involved in the study. “Until now, [brain-computer interfaces have] primarily focused on motor activities (such as limb movement or speech).”

The project is yet another example of booming interest in this field. Last year, researchers at UCSF deciphered brain signals from a paralyzed man who hadn’t spoken in over 15 years and used his attempts to speak to generate more than 1,100 words that appeared on a screen.

In 2021, the Food and Drug Administration approved a device from Neurolutions designed to help stroke patients regain the ability to move their hands, wrists, and arms. And there’s a growing list of companies looking to capitalize on brain-computer interfaces, from Blackrock Neurotech to Neuralink, founded by Elon Musk. Despite the surge of enthusiasm and investment dollars, observers say that if these companies develop effective technologies, they’ll face another major challenge — turning devices that are expensive to make and typically require brain surgery to implant into profitable products.

Lee said that this study could help scientists design brain-computer interfaces that help paralyzed patients move more efficiently than interfaces implanted into brain regions that directly control limb movement. Instead of thinking about taking a specific number of steps in a particular direction, he said, a person might reach their refrigerator simply by thinking of standing in front of it and having a brain-computer interface read signals from their hippocampus and relay that to a prosthetic.

That’s still a far-off possibility. In the short term, researchers are focused on testing the limits of the rodents’ imaginative abilities. They want to re-run the experiments in the dark, so that the animals would have fewer cues from the virtual environment. Scientists also plan to test whether the rats can imagine traversing longer distances in a larger virtual world, as well as how other regions of the brain influence the ability of the hippocampus to create and modify its internal model of the world.

“It actually gives us a pretty good amount of intuition about what might be going on when humans are imagining scenarios,” said Lee of the recent study. “That will help guide us in our future experiments.”