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March 01, 2013

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Study links rat brains together electronically

March 1, 2013
Courtesy of Duke University Medical Center
and World Science staff

Re­search­ers say they have elec­tron­ic­ally linked the brains of pairs of rats, en­a­bling them to com­mu­ni­cate di­rectly to solve sim­ple puz­zles.

A fur­ther test suc­cess­fully linked the brains of two an­i­mals thou­sands of miles apart, ac­cord­ing to the re­search­ers. The re­sults, they add, sug­gest the fu­ture po­ten­tial for link­ing mul­ti­ple brains to form an “or­ganic com­put­er,” which could al­low shar­ing of in­forma­t­ion among groups of an­i­mals. 

Courtesy Duke University Medical Center
The study was pub­lished Feb. 28 in the jour­nal Sci­en­tif­ic Re­ports.

Past stud­ies “had con­vinced us that the rat brain was much more plas­tic,” or ad­apt­able, “than we had pre­vi­ously thought,” said Mi­guel Nicolelis, the lead au­thor and a neuro­bi­ol­o­gist at Duke Uni­vers­ity School of Med­i­cine in Dur­ham, N.C.

“The rat brain was able to adapt easily to ac­cept in­put from de­vices out­side the body,” called brain-machine in­ter­faces, “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?’“

To test that, the re­search­ers first trained pairs of rats to press the cor­rect lev­er when an in­di­ca­tor light above the lev­er switched on, which re­warded the rats with a sip of wa­ter. They next con­nect­ed the two an­i­mals’ brains via elec­tri­cal con­nec­tions in­sert­ed in­to the ar­ea of the cor­tex, part of the brain, that pro­cesses in­forma­t­ion on phys­i­cal move­ment.

One of the ro­dents was des­ig­nat­ed as the “en­coder.” This an­i­mal re­ceived a vis­u­al cue that showed it which lev­er to press. Once this “en­coder” rat pressed the right lev­er, a sam­ple of its brain ac­ti­vity that cod­ed its de­ci­sion was trans­lated in­to a pat­tern of elec­tri­cal stimula­t­ion that was de­liv­ered di­rectly in­to the brain of the sec­ond rat, known as the “de­coder” an­i­mal.

The de­cod­er rat had the same types of lev­ers in its cham­ber, but re­ceived no vis­u­al cue in­di­cat­ing which lev­er it should press to get a re­ward. To press the cor­rect lev­er, the de­cod­er rat would have to rely on the cue trans­mit­ted from the en­cod­er.

The de­cod­er rat ul­ti­mately achieved a max­i­mum suc­cess rate of about 70 per­cent, the re­search­ers said. This was only slightly be­low the pos­si­ble max­i­mum suc­cess rate of 78 per­cent that they had the­o­rized was achieva­ble based on suc­cess rates of send­ing sig­nals di­rectly to the de­cod­er rat’s brain.

Im­por­tant­ly, this “brain-to-brain in­ter­face” de­vice pro­vid­ed two-way com­mu­nica­t­ion, they added. For in­stance, the en­cod­er rat did not re­ceive a full re­ward if the de­cod­er rat made a wrong choice. The re­sult of this pe­cu­liar con­tin­gen­cy, said Nicolelis, led to the es­tab­lish­ment of a “be­hav­ioral col­la­bora­t­ion” be­tween the pair of rats.

“We saw that when the de­cod­er rat com­mit­ted an er­ror, the en­cod­er bas­ic­ally changed both its brain func­tion and be­hav­ior to make it eas­i­er for its part­ner to get it right,” Nicolelis said. “The en­cod­er im­proved the sig­nal-to-noise ra­tio of its brain ac­ti­vity that rep­re­sented the de­ci­sion, so the sig­nal be­came clean­er and eas­i­er to de­tect. And it made a quick­er, clean­er de­ci­sion to choose the cor­rect lev­er to press. In­var­i­a­bly, when the en­cod­er made those adapta­t­ions, the de­cod­er got the right de­ci­sion more of­ten, so they both got a bet­ter re­ward.”

The re­search­ers even placed an en­cod­er rat in Bra­zil, at the Ed­mond and Lily Safra In­terna­t­ional In­sti­tute of Neu­ro­sci­ence of Na­tal, and trans­mit­ted its brain sig­nals over the In­ternet to a de­cod­er rat in Dur­ham, N.C. They found that the two rats could still work to­geth­er.

“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 co-au­thor of the stu­dy. “This tells us that it could be pos­si­ble to cre­ate a worka­ble net­work of an­i­mal brains dis­trib­ut­ed in many dif­fer­ent loca­t­ions.”

* * *

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Researchers say they have electronically linked the brains of pairs of rats, enabling them to communicate directly to solve simple puzzles. A further test successfully linked the brains of two animals thousands of miles apart, according to the researchers. The results, they add, suggest the future potential for linking multiple brains to form an “organic computer,” which could allow sharing of motor and sensory information among groups of animals. The study was published Feb. 28 in the journal Scientific Reports. Previous studies “had convinced us that the rat brain was much more plastic,” or flexible, “than we had previously thought,” said Miguel Nicolelis, lead author of the publication and neurobiologist at Duke University School of Medicine in Durham, N.C. “The rat brain was able to adapt easily to accept input from devices outside the body,” called brain-machine interfaces, “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?’“ To test that, the researchers first trained pairs of rats to press the correct lever when an indicator light above the lever switched on, which rewarded the rats with a sip of water. They next connected the two animals’ brains via electrical connections inserted into the area of the cortex, part of the brain, that processes information on physical movement. One of the rodents was designated as the “encoder.” This animal received a visual cue that showed it which lever to press. Once this “encoder” rat pressed the right lever, a sample of its brain activity that coded its decision was translated into a pattern of electrical stimulation that was delivered directly into the brain of the second rat, known as the “decoder” animal. The decoder rat had the same types of levers in its chamber, but received no visual cue indicating which lever it should press to get a reward. To press the correct lever, the decoder rat would have to rely on the cue transmitted from the encoder. The decoder rat ultimately achieved a maximum success rate of about 70 percent, the researchers said. This was only slightly below the possible maximum success rate of 78 percent that they had theorized was achievable based on success rates of sending signals directly to the decoder rat’s brain. Importantly, the communication provided by this brain-to-brain interface was two-way, they added. For instance, the encoder rat did not receive a full reward if the decoder rat made a wrong choice. The result of this peculiar contingency, said Nicolelis, led to the establishment of a “behavioral collaboration” between the pair of rats. “We saw that when the decoder rat committed an error, the encoder basically changed both its brain function and behavior to make it easier for its partner to get it right,” Nicolelis said. “The encoder improved the signal-to-noise ratio of its brain activity that represented the decision, so the signal became cleaner and easier to detect. And it made a quicker, cleaner decision to choose the correct lever to press. Invariably, when the encoder made those adaptations, the decoder got the right decision more often, so they both got a better reward.” In further experiments, the researchers trained pairs of rats to distinguish between a narrow or wide opening using their whiskers. If the opening was narrow, they were taught to nose-poke a water port on the left side of the chamber to receive a reward; for a wide opening, they had to poke a port on the right side. The researchers then divided the rats into encoders and decoders. The decoders were trained to associate stimulation pulses with the left reward poke as the correct choice, and an absence of pulses with the right reward poke as correct. During trials in which the encoder detected the opening width and transmitted the choice to the decoder, the decoder had a success rate measured at about 65 percent. The researchers even placed an encoder rat in Brazil, at the Edmond and Lily Safra International Institute of Neuroscience of Natal, and transmitted its brain signals over the Internet to a decoder rat in Durham, N.C. They found that the two rats could still work together. “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 co-author of the study. “This tells us that it could be possible to create a workable, network of animal brains distributed in many different locations.”