In a groundbreaking study published earlier this year in Scientific Reports, a team of scientists has demonstrated that it's possible for a rat to transmit information directly into the brain of another rat.
In the past decade, increasingly sophisticated brain-machine interfaces have been developed to allow test animals—and more recently, human patients—to mentally control a robotic limb or move a cursor on a screen. The team, led by neurobiologist Dr. Miguel Nicolelis at the Duke University Medical Center, decided to take brain-machine interfaces to the next level.
"Our previous studies with brain-machine interfaces had convinced us that the brain was much more plastic than we had thought," Nicolelis said in a press release. "In those experiments, the brain was able to adapt easily to accept input from devices outside the body and even learn how to process invisible infrared light generated by an artificial sensor. So, the question we asked was, if the brain could assimilate signals from artificial sensors, could it also assimilate information input from sensors from a different body."
Two Bodies, One Mind
The researchers implanted pairs of rats with arrays of microelectrodes, devices a fraction of the width of a human hair, that lie directly on the surface of the brain. For each pair, one rat was dubbed the encoder; the other, the decoder. In a series of trials, the encoder rat was trained to perform a task in exchange for a sip of water, and the electrode array recorded its brain activity. Then that recorded activity was transmitted to the decoder rat’s brain, stimulating the electrodes in its brain in precisely the same pattern. By using its partner’s pattern, the decoder rat was able to make better decisions than it could on its own.
And learning went in both directions. The scientists designed the experiment so that when the decoder rat successfully performed its task, the encoder rat would receive an additional reward. Very quickly, the encoder rat learned to modify its brain activity, creating a smoother, stronger signal for its partner to read. The longer the two rats worked together, the more they altered their behavior to form a working team.
In one trial, the encoder rat was taught to pull a lever on the right or left of its cage when a light appeared over the lever, with about 95 percent accuracy. In the cage next to it, its partner, the decoder rat, was trained to pull the right or left lever, depending on a signal the scientists transmitted into its brain, with about 78 percent accuracy. Then, to test whether the encoder rat could teach the decoder rat which lever to pull, the scientists transmitted the encoder rat’s brainwaves to the decoder rat in real time.
Using the information received from the encoder rat, the decoder rat was able to pull the correct lever 70 percent of the time, far more accurately than chance would allow. When the decoder rat made a mistake, the encoder rat focused more and improved the quality of the signal it was sending to its friend. When the scientists switched the interface machine off, the decoder rat’s performance dropped back to no better than random chance.
To investigate the extent to which the two rats could align their senses, the team looked closely at the group of brain cells that processed information from the rats' whiskers. As in humans, the cells formed a “map” of the sensory input they were receiving. They found that after a period of transmitting the brain activity from the encoder rat into the decoder rat, the decoder rat's brain began to map out the encoder rat’s whiskers alongside its own.
This last finding is very promising for the advancement of prosthetics for people who have been paralyzed or suffered other nerve damage. It suggests that humans might able to not only learn to control a robotic limb, but also remap their brains to receive sensory information from the limb itself.
In the ultimate test of their technology, Nicolelis’s team decided to link together two rats in different countries. They partnered a rat in their lab in Durham, North Carolina, with a rat in a lab in Natal, Brazil. Despite thousands of miles over which the signal could degrade, the two rats were able to work together and cooperate in real time.
"So even though the animals were on different continents, with the resulting noisy transmission and signal delays, they could still communicate," said Miguel Pais-Vieira, a postdoctoral fellow and first author of the study, in a press release. "This tells us that we could create a workable network of animal brains distributed in many different locations."
Dawn of the Cyborg?
Right now, they’ve only linked two rats, but the researchers are working on building connections between groups of rats to see if they can collaborate on more complex tasks.
"We cannot even predict what kinds of emergent properties would appear when animals begin interacting as part of a brain-net,” Nicolelis said. “In theory, you could imagine that a combination of brains could provide solutions that individual brains cannot achieve by themselves."
Nicolelis’s discovery is on the vanguard of the expanding field of cybernetics. Crude structures like limbs aren’t the only robotic prostheses in development. A bionic eye was recently approved by the U.S. Food and Drug Administration (FDA).
Modern prosthetics even extend to the brain itself—a recent invention by Dr. Theodore Berger could allow one brain region to be replaced by a computer chip. In his study, Berger removed the hippocampus from rats, the brain region that allows all mammals to form new memories. Without a hippocampus, a rat cannot learn to run a maze.
In its place, he installed a chip that modeled the behavior of the hippocampus. Using the chip, the rat was able to learn to run the maze just fine; remove the chip, and the learning is gone. Whether another rat could then run the maze using the same chip remains untested, but Nicolelis’s research suggests it might be possible.