2023-11-02 20:00:09
To construct reality, human beings constantly use our imagination, a capacity that allows us elaborate thoughts and memories. These can range from daydreaming about traveling to remote places, to much simpler things like what are we going to do for lunch today.
Scientists of the Howard Hughes Medical Institute (HHMI) in the United States have discovered that other animals also have imagination. To do this, a team from the laboratories Lee y Harris developed a novel system that combines virtual reality (VR) and one brain-machine interface (BMI)for its acronym in English) that probes the internal thoughts of rats.
Until now it was known that when these animals experience places and events, specific patterns of neuronal activity are activated in the hippocampus, an area of the brain responsible for spatial memory. With their experiments, they observed that rats could voluntarily generate these same activity patterns and do so to remember places far from their current position.
“In effect, the rat can activate the representation of places in the environment without being there. Although its physical body is fixed, its spatial thoughts can go to a very remote place,” he says. Chongxi Lairesearcher at both laboratories and first author of the article, published this week in Science.
An interface that ‘detects thought’
This project began nine years ago, when Lai arrived at HHMI’s Janelia Research Campus as a graduate student. Her main idea was to test if an animal could think. Her advisor Tim Harrisfrom the same institution, suggested that he come talk to the Lee laboratory, where similar questions were being asked.
In this way, the initiative arose to create a system that would allow us to understand what animals think: a real-time “thought detector” capable of measuring neural activity and translating its meaning.
The system uses the Interface brain-machine, which provides a direct connection between brain activity and an external device. This technology allows a link to occur between the electrical activity of the rat’s hippocampus and its position in a 360-degree virtual reality scenario.
“‘Thought detectors’ that are implanted in very deep brain tissues, such as the hippocampus. They can decode abstract thinking, not only limited to space, but also other abstract concepts. They can therefore be used for brain-machine interfaces personalized,” Lai explains to SINC.
When we generate a memory, this causes activity patterns to be generated in the hippocampus related to places and events. But until now it was not known whether animals could voluntarily control this activity.
“This is a fundamental element that underlies the ability to place ourselves in the past or the future, in certain scenarios. My hypothesis is that this ability is extrapolated to other species that have a hippocampus and brain structures similar to the hippocampus,” continues the scientist.
A dictionary of what we think
After developing the system, the researchers had to create a “dictionary of thoughts” that would allow them to decode the rat’s brain signals. In this way, they collected what the brain activity patterns are like when the rat experiences something, in this case, seeing places in the virtual reality scenario.
They introduced the animal into the system designed by Shinsuke Tanaka, from the Lee laboratory, and while the rat walked along a spherical belt, its movements were reflected on the 360-degree screen. When he reached his set goal, he was rewarded.
At the same time, the system recorded the activity of its hippocampus so that it could be seen which neurons were activated when the rat navigated the arena to reach each objective. These signals form the basis of real-time hippocampal BMI. Brain activity translates into actions on the screen.
“The ‘thought detector’ translates the spike pattern of many neurons produced in the hippocampus into a coordinate of a specific location. When we are in a certain place, and yet we think about another remote place, some of our neurons will change their firing to represent that remote place. This decoder can detect it and read where the animal was thinking,” adds Lai.
The first test they gave was to disconnect the tape and reward the rat for reproducing the pattern of hippocampal activity associated with the location of a target. In this homework, called ‘Jumper’ Per a 2008 film of the same name, BMI translates the animal’s brain activity into motion on the virtual reality screen. That is, the rat uses its thoughts to reach the reward and first thinks about where it has to go to get it. This thought process is something we humans experience regularly.
In the second task, ‘Jedi’ —a nod to Star Wars—the rat had to move an object to a place with just his thought. The animal remained fixed in a virtual location, but ‘moved’ an object towards a target in VR space by controlling its hippocampal activity, like a person sitting in their office who imagines picking up a cup next to the coffee maker and filling it with coffee. Next, the researchers changed the target location, requiring the animal to produce activity patterns associated with the new location.
“Rats move objects using spatial attention. Imagine if such a ‘thought decoder’ were implanted in our brain and programmed to guide the movement of an external object around it. It would realize it and also be able to control that object very soon,” Lai reflects.
That’s when they discovered that rats can precisely and flexibly control their hippocampal activity, the same way humans probably do. Furthermore, animals are able to maintain this activity in the hippocampus for several seconds, a time similar to the time it takes for humans to relive past events or imagine new scenarios.
“The amazing thing is how they learn to think in that place, and nowhere else, for a very long period of time, based on our perhaps naive notion of a rat’s attention span,” Harris says.
The research also shows that the brain-machine interface can be used to probe hippocampal activity, providing an novel system to study this important brain region. As BMI is increasingly used in prosthetics, it also opens up the possibility of designing new prosthetic devices based on the same principles, according to the authors.
Reference:
Chongxi Lai et al. “Volitional activation of remote place representations with a hippocampal brain–machine interface”. Science2023
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