Whether dreaming of a white Christmas or simply pondering how best to rearrange the furniture, humans are able to conjure up myriad situations that are not in front of us. Now it seems rats may be able to do something similar.
Researchers have found that rats can navigate their way through a space they have previously explored using their thoughts alone, suggesting the rodents have some sort of imagination.
Chongxi Lai, the first author of the study from the Howard Hughes Medical Institute Janelia Research Campus, said the study was the first to show animals can, at will, flexibly activate the brain’s representations of places that are distant from where they currently are.
“This is a fundamental building block of a specific type of imagination, one that enables us to project ourselves into the past or future, within a certain scenario,” he said.
Writing in the journal Science, the researchers note that a region of the brain called the hippocampus contains a sort of mental model, or map, depicting previously explored environments. When an individual moves through specific locations within such an environment, particular neurons fire in the brain.
However, humans can, at will, imagine navigating their way through places they have previously visited – for example the corridors of a workplace.
To explore whether rats can do the same, and unpick a possible mechanism, researchers employed a brain-machine interface in which electrodes were surgically implanted into the rats’ brains. The rats were then placed on a treadmill ball within a 360-degree immersive virtual reality (VR) arena, and presented with an on-screen goal to run towards.
As the rats moved, and the treadmill ball turned, the animal’s apparent location within the VR environment updated on screen – as if the rat was running through a real environment. When the rats reached the goal, they received a treat and the goal was moved within the VR environment. The process was then repeated.
During this initial phase, the team recorded the activity within the animals’ hippocampus. They then used a computer system to translate this neural activity to specific locations within the VR environment.
In the next step, the researchers decoupled the treadmill from the VR system. This meant the rats could not reach the goal by running on the treadmill. Instead, they could only use their brain activity to navigate through the VR environment.
By analysing the activity in rats’ hippocampus in real time during the task, the team were able to update the screen every 100 milliseconds with the animals’ current location in the VR environment, based on what was happening in their brain.
The results reveal the rats could indeed navigate to the goal using just their brain activity.
In a subsequent experiment, the team gave the rats a “Jedi task” in which the animals themselves were stationary but had to direct an object on the screen to a particular goal within the VR environment using only their brain activity. Once again, the rats were able to do so.
Prof Tim Harris, another author of the work at the Howard Hughes Medical Institute, said it was thought that in humans, imagination and recall is linked to activity in the hippocampus similar to that which occurs in the real-life scenario.
“To this end, it is fair to say the rats do imagine,” he said.