Close your eyes and imagine yourself running to your kitchen to grab a snack. You can probably imagine the setting of the rooms and the turns you’d need to get there. This ability to visualize paths has been known exclusive and crucial to humans for efficient future planning. But this ability may not uniquely be ours.
Researchers reporting to the Science magazine described rodents trained to navigate through a virtual maze for a sugary reward, to be able to excite the same neural pathways while standing still, suggesting that they can voluntarily access mental maps of places they have previously been to.
“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 in the research. “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.
Contemporary science suggests that these mental maps for humans are encoded in the hippocampus - a site in the brain involved with memory. When we move through an environment, a particular neural pattern excites, and can later be mimicked in the same sequence when we even as little as think about going through it again.
The same is true for rats. However, it is much more difficult to establish this because of the practical challenges of making a rodent think about a particular place on cue. Later Chongxi Lai, along with Janelia neuroscientist Albert Lee and colleagues found a way to circumvent this issue by developing a brain-machine interface that rewarded rats for navigating their surroundings by only their thoughts.
To begin, the team devised a miniature virtual reality setup, projecting it onto a screen surrounding a spherical treadmill, resembling a trackball from a computer mouse. Rats were able to explore this virtual arena by running on the treadmill, with the promise of a sugary reward if they reached specific objects within it. Meanwhile, the team continuously monitored the rats' hippocampal brain activity during their journeys.
Subsequently, Lai and their colleagues disconnected the treadmill, allowing the rats to still perceive the virtual reality arena but removing the physical impact of their running. Instead, they linked the display to real-time recordings of the rats' brain activity. By reproducing the same brain patterns seen during their earlier training sessions, the rats could navigate to reward locations solely through their thoughts. Some rats continued to run on the treadmill fruitlessly, while others remained motionless during this process.
Such researches are crucial for understanding how brains process information, and additionally, what other species of this world think like.
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