brain

Powers of perception

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BRAINS get data about the world through senses – sight, hearing, taste, smell and touch. In a lab in North Carolina, a group of rats is getting an extra one. Thanks to implants in their brains, they have learned to sense and react to infrared light. The rats show the brain’s ability to process unfamiliar data– an early step towards augmenting the human brain.

Miguel Nicolelis of Duke University School of Medicine is leading the experiment. His team implanted four clusters of electrodes in the rats’ barrel cortex – the part of the brain that handles whisker sensation (doi.org/bdb6). Each cluster is connected to a sensor that converts infrared light into an electrical signal. Feeding stations placed at the four corners of the rats’ cage take turns emitting infrared signals that guide the rats to them, releasing a reward only when the rats press a button on the feeding station that is emiting the infrared signal.

In an older, single sensor version of the experiment, it took the rats one month to adapt. With four sensors, it took them just three days.

“This is a truly remarkable demonstration of the plasticity of the mammalian brain,” says Christopher James of the University of Warwick, UK.

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All the extra data that goes into making the rats’ new sense doesn’t appear to diminish their original senses. “The results show that nature has apparently designed the adult mammalian brain with the possibility of upgrades, and Nicolelis’ team is leading the way showing how to do it,” says Andrea Stocco of the University of Washington in Seattle.

Nicolelis says unpublished data from a follow-up experiment shows that rats learn even faster when the sensors feed directly into their visual cortex, taking just 6 or 7 hours. Nicolelis thinks the speed-up comes from using a part of the brain that already interprets light. He is planning a subsequent experiment in which the rats can only get a reward if they “see” both parts of the spectrum at once, visual and infrared.

And if it could be done with infrared, why not with ultraviolet light, microwaves, or other inputs? “It would be a fusion, total vision,” says Nicolelis.

“It seems that nature designed the adult mammalian brain with the possibility of upgrades“

“Now there’s no doubt that it’s easy for the mammalian brain, even in adulthood, to adaptively use a novel, never-experienced sense, such as infrared,” says Yuji Ikegaya of the University of Tokyo in Japan.

Nicolelis’ brain interfaces will probably find their first application in the medical world, but they are part of a trend that erodes the boundary between our brain and the outside world. Human beings already implant sensors and chips in their flesh, and although implanting in the brain is dangerous, the benefits may outweigh the risks someday.

“Is it safe, and are these capabilities we necessarily want to develop?” asks Filippa Lentzos of King’s College London. “Could it be abused by the military, to enhance battlefield performance or degrade enemy performance?”

But Lentzos points out that implants such as hearing aids are widely offered to patients. “We do a lot of this already, so whether completely new senses would be acceptable is a very interesting debate.”

This article appeared in print under the headline “How to make senses”

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