In a story that might have come from science fiction, neuroscientists at Duke University (Durham, NC) directly linked the brains of two rats, enabling them to share information. Once trained in a simple task—pressing a lever corresponding to an indicator light or correctly identifying an opening in a barrier as wide or narrow in order to obtain a reward—pairs of rats were connected via implanted microelectrode arrays and placed in separate cages.

Only one of the rats, the 'encoder,' was exposed to the stimulus (the indicator light or the opening), and upon completion of the task, its brain activity was recorded and transmitted to the other, 'decoder,' rat. The decoder rat then had to select the correct response based solely on the information it received from the encoder rat. The decoder rats achieved success rates of ∼70% in the indicator light test and ∼65% in the opening width test (Sci. Rep. 3, 1319; 2013).

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The scientists even paired two rats located on different continents, transmitting the brain signal over the internet. Although the decoder rat's response time was longer, its success rate was similar to that of rats that were geographically co-located.

Nicolelis explained, “These experiments demonstrated the ability to establish a sophisticated, direct communication linkage... creating a single central nervous system made up of two rat brains.”

But the value and applications of the work are under debate. Christopher James (University of Warwick, UK), who works on brain–machine interfaces but was not associated with the project, told New Scientist that it's unclear exactly what information is being communicated between the rats. The experiments, he said, “blast[ed] a relatively large area of the brain with a signal they're not sure is 100% correct. We are still using a sledgehammer to crack a walnut.” Andrew Schwartz (a neurobiologist at University of Pittsburgh, PA) noted in a Nature News story that the decoder rats performed relatively poorly given a basic task with only two choices and a 50% success rate expected by chance. Lee Miller (a physiologist at Northwestern University, Evanston, IL) told Nature News, “It is not clear to what end the effort is really being made.” Sliman Bensmaia, a neuroscientist from the University of Chicago (IL), added that if Nicolelis's goal was to improve neural prosthetics, then “the design seems convoluted and irrelevant,” and if the goal was to build a computer, then “the proposition is speculative and the evidence underwhelming.”