Humans use their imaginations regularly, from mentally mapping out the fastest route to the office to considering what to make for dinner. Now, new research suggests rats may have imaginations, too.
More specifically, the findings indicate rats, like humans, can use their brains to imagine walking to a new location or moving a virtual item to a new place, even when they are physically sitting still, according to a new study published last week in the journal Science.
Imagination has long been considered a uniquely human trait that involves thinking about something that’s not actually happening—like picturing yourself back on the beach from your last vacation.
Scientists think much of the human imagination is controlled by the hippocampus, a region of the brain that plays a role in memory and learning. For example, when humans navigate from place to place, the hippocampus lights up with a specific pattern of activity depending on the location. Later, when thinking about moving through the same environment, the same patterns appear in the hippocampus—sort of like a built-in GPS system, as Mark Johnson writes for the Washington Post.
The hippocampus is also involved in rats’ spatial memory. But researchers have long wondered whether the rodents can navigate an environment using just their thoughts, like humans can. The problem, until now, was finding a way to test that.
For the new experiment, scientists spent years developing virtual reality for rats—a brain-machine interface that could help them answer this question. First, they implanted electrodes into the animals’ brains to record activity in their hippocampi. Then, they suspended the animals in harnesses just above a ball-shaped treadmill—similar to a computer mouse trackpad—and surrounded them with a 360-degree screen depicting a virtual reality arena.
As the rats ran on the spherical treadmill, they moved through the virtual environment on the screen. Researchers trained them to navigate to specific areas by rewarding them with a sip of sugar water. At each spot the rats visited in the computerized arena while moving their feet on the treadmill, their hippocampi produced a distinctive activity pattern. The team trained their technology to recognize these patterns and match them to the corresponding virtual locations.
The scientists suspected the rodents could reproduce those brain patterns by simply thinking about each location. So, in another part of the experiment, they disconnected the treadmill, leaving the rats to navigate the virtual reality arena using only their minds. In this task, named “Jumper” after the 2008 film about teleportation, the brain-machine interface translated the animals’ neural activity into motion on the screen. When the rats recreated the hippocampal activity associated with a specific location, the screen jumped to that site—and the rats got a reward.
In another experiment, dubbed the “Jedi” in a nod to Star Wars, the rats used their thoughts to imagine moving a virtual object to a location while they stayed in the same place.
“The rat can indeed activate the representation of places in the environment without going there,” says study co-author Chongxi Lai, a neuroscientist who conducted the research while at Howard Hughes Medical Institute but now works at Beth Israel Deaconess Medical Center, in a statement. “Even if his physical body is fixed, his spatial thoughts can go to a very remote location.”
Three of the four rats tested were able to navigate the virtual reality tasks, per the Washington Post. Together, the findings indicate rats can mentally navigate environments they’ve visited in the past, just like humans do. Rats can also, it seems, hold their thoughts on a specific location for several seconds.
“We know humans carry around inside their heads representations of all kinds of spaces: rooms in your house, your friends’ houses, shops, libraries, neighborhoods,” says Sean Polyn, a psychologist at Vanderbilt University who was not involved with the new study, to Science’s Catherine Offord. “Just by the simple act of reminiscing, we can place ourselves in these spaces—to think that we’ve got an animal analog of that very human imaginative act is very impressive.”
Still, it remains unclear whether rats experience this mental mapping process the same way humans do. It’s possible the rats are not actively imagining the locations, but rather, their hippocampi may just be subconsciously predicting what’s next, says Matthew Wilson, a neurobiologist at MIT who was not involved in the research, to Scientific American’s Jack Tamisiea.
“Right now, it’s like they’re imagining the next frame of a movie while they’re watching it,” he tells the publication. “But imagination is what happens when you close your eyes and you create these perceptions internally.”