It's not quite telepathy, but it's the closest anyone has ever come to getting a mammal to read another mammal's mind.
A research team led by neurobiologist Miguel Nicolelis of Duke University has wired together the brains of two rats, allowing them transmit information between each other and cooperate.
The results, detailed in the journal Scientific Reports, could help improve the design of neural-controlled prosthetic devices. And perhaps more than that, they also show that one day we could network brains as well as computers, or communicate by translating neural activity in the brain into electronic signals.
In the experiment, the Duke scientists first trained two rats to press one of two levers when a particular light switched on. Next, they then connected the animals' brains with tiny electrodes, each a fraction the size of a human hair. The electrodes linked the parts of the rats' brains that process motor signals.
Rat number one was called the "encoder" and rat number two was the "decoder." The first rat's job was to receive the visual cue to press the lever. If it got it right, it got a reward.
As the encoder rat did its task, the electrical activity in the encoder rat's brain was then translated into a signal and transmitted to the decoder rat. That rat would then press its own lever. For the second rat, though, there was no light cue to tell it which corresponding lever was correct. It could only go by the signal it received from the other rat.
It hit the correct lever an average of about 64 percent of the time, and sometimes up to 72 percent -- much better than if it were only doing it by chance.
To confirm that this was an effect of the signals from the encoder rat's brain, Nicolelis and his team gave the decoder rat the same stimulation, but this time from a computer. They got a similar result.
Another experiment tested whether the rat's brain could transmit information about touch. This time the rats were trained to put their nose through an opening and, using their whiskers, distinguish whether the opening was wide or narrow. For wide openings, the rats were taught to poke a computer port on their right. For narrow openings, they poked to the left.
Once trained, the rats were wired up to each other. When the encoder rat poked the relevant port, the scientists recorded the brain activity and sent the signal to the decoder rat. The decoder chose the correct side – left or right – to poke 60 to 65 percent of the time.
As an added twist, the encoder rat got an additional reward if the decoder rat made the right choice. Since the encoder rat wanted the extra reward, it would try to do the task better. That actually refined the signal in its brain, making it clearer. Once the decoder rat got the stimulation, it made the right choice – giving the first rat the extra reward.
The group even tried the same experiment using an Internet connection with another lab in Brazil. The Internet is rather noisy – signals don't travel perfectly, as anyone who has listened to a Wi-Fi or Skype call can attest. But in this case the results were similar to what they got in the lab when the rats were in close proximity.
But besides being able to transmit signals, Nicolelis found something new after the rats practiced the whisker task for about a month. He looked at the way the first rat's brain responded to its whiskers getting touched and saw a characteristic pattern of activity. Touch the second rat's whiskers and something similar happened, as expected. But after being linked for a period of time the second rat's brain responded to touches on the first rat's whiskers.
This is an important point, Nicolelis said, because it gets to how animals understand their own bodies – how a person knows that the hand is hers rather than someone else's. It's quite possible, he said, that our sense of self -- our model of our bodies -- has something to do with how we interact with other people.
Another question is what the rats are feeling when all this is happening. It's not possible to tell, except by watching their behavior. "It would be interesting to know what the subjective experience is like but the rats cannot tell me," Nicolelis said.
Jean-François Gariépy, post-doctoral researcher at the Center for Cognitive Neuroscience, Duke University, who was not involved in the study, called it an important step, because it links getting information out of the brain – reading it – and getting information into the brain. "It's a big challenge because you want to send signals that are strong enough to be detected by some neurons and you want the signal to be fine enough to mean something, to contain information," he wrote in an email. " connects the two types of [brain-machine interfaces]: those that extract information and those that send information."
But not everyone is convinced that this experiment is a major step. Andrew Schwartz, professor of neurobiology at the University of Pittsburgh who has done extensive research on brain-computer interfaces, said the experiment was a bit too simple because it only involved a binary decision – a yes/ no. "Brain-computer interface technology and demonstrations have moved far beyond this," he said, likening it to a locked-in patient communicating by blinking. "This kind of information could be conveyed by recording from a single neuron in one rat and buzzing electrical current in the receiver rat. If the rat feels the buzz it means yes, no buzz means no."
Nicolelis said the simplicity of the experiment is not a fault. "That is how we start the entire field of brain machine interfaces: with a simple rat experiment that defined a paradigm that Dr. Schwartz has been using for 15 years without any change whatsoever. Simple things are elegant and may lead to big things eventually!"