Rats can move an object in virtual reality using only their thoughts, demonstrating the same ability humans use when re-living past events or imagining new scenarios.
“To imagine is one of the remarkable things that humans can do. Now we have found that animals can do it too, and we found a way to study it,” says Dr Albert Lee, an author of the paper published in Science.
The hippocampus in the brain is used for memory, imagination and future planning. It contains a cognitive map of previously explored environments and the ability to simulate scenarios, a hallmark of intelligence.
To test the ability of rats to control their hippocampal activity, the team of researchers from the Howard Hughes Medical Institute in the US fitted the rodents with a brain machine interface connected to a virtual reality arena.
The brain machine interface enabled the researchers to detect the rats’ thoughts by measuring neural activity in the hippocampus, translating this into a position within the virtual reality arena. This was necessary, the paper points out, because “we cannot simply ask animals to imagine scenarios”.
Once fitted with the device, the rats were set two tasks.
In the first, the rats – secured in a harness but able to move on a treadmill – ran towards a goal within a virtual 2-dimensional arena, to receive a reward. The pace and direction of the rats’ movement on the treadmill updated its virtual location within the arena.
The animals performed this task many times over for approximately 40 minutes.
Data collected during the running task was then used to train the virtual reality system so that movement within the game was tailored to the rat’s movement in the first task.
A second “Jedi” task, then tested the rats’ ability to move objects in virtual reality, in this case using only their minds.
“Even if his physical body is fixed, his spatial thoughts can go to a very remote location,” says author Chonxi Lai.
In the Jedi task, the treadmill was removed. Rats performed the same task while stationary – moving an object towards a goal in virtual reality and holding it there – “by means of BMI-based first-person teleportation”, the paper explains. Like in the first task, rats were rewarded each time they reached a goal in virtual reality.
Throughout these tasks, the rats’ neural activity was recorded using the brain machine interface.
Similar to the way humans might imagine a journey or task in advance before leaving the house, the rat uses thoughts to navigate towards the reward by first thinking about where they need to go to get there.
Imagination involves holding a single thought in mind for extended periods, involving new scenarios. In both tasks, the rats demonstrated their ability to precisely and flexibly control their hippocampal activity.
“Rats could activate and sustain a remote location’s representation around the goal for long periods, until the trial ended, and then shift attention to the next goal,” the authors write.
The animals were able to perform this task with minimal physical movement and without extensive training.
The results show that rats possess a form of imagination, the ability to voluntarily picture locations away from their current position, and plan for future scenarios, in the same way humans likely do.
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