Scientists have moved closer to allowing paralysed people to control artificial limbs with their thoughts following a breakthrough in technology that gave rats an extra sense.
A brain implant that allows the animals to "feel" the presence of invisible infrared light could one day be used to provide paralysed people with feedback as they move artificial limbs with their thoughts, or it could even extend a person's normal range of senses.
Miguel Nicolelis, a neurobiologist at Duke University in North Carolina who led the work, is a pioneer in the development of brain implants that can be used to control computers or prosthetic arms by thought alone.
His aim is to develop ways to help paralysed people regain mobility and ultimately to build an "exoskeleton" that can move a paralysed person's arms and legs in response to their thoughts.
Nicolelis was speaking about his latest work, which was published in Nature Communications, at the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston.
His results were presented as part of a series of sessions on advances in brain-machine interfaces, at which other scientists presented a bionic hand that could connect directly to the nerves in a person's arm and provide sensory feedback of what they were holding.
Until now, neurological prosthetics have largely been demonstrated as a way to restore a loss of function. Last year, a 58-year-old woman who had become paralysed after a stroke demonstrated that she could use a robotic arm to bring a cup of coffee to her mouth and take a sip, just by thinking about it.
The work was part of a US clinical trial of a brain implant called BrainGate, developed by neuroscientists at Brown University in Rhode Island.
In his latest work, Nicolelis has created the first device to extend a healthy animal's natural ability. "What we did here was to demonstrate that we could create a new sense in rats by allowing them to 'touch' infrared light that mammals cannot detect."
He inserted an electrode into the part of a rat's brain that processes touch and fed into it electrical signals that corresponded to a local source of infrared light. After a month of training, Nicolelis found that rats' touch-processing brain cells were responding to both touch and infrared light at the same time. "This shows that the adult brain can acquire new capabilities that have never been experienced by the animal before," he said.
In the future, Nicolelis said it might be possible to use prosthetic devices to restore vision - for example, if a person's visual cortex had been damaged - by training a different part of the brain to process the information.
"Or you could even augment normal brain function using the principles we're describing here in non-invasive ways to deliver the information," he said.
"We could learn to detect other sorts of signals that we normally don't see or experience; perceptual range could increase."
Also at the AAAS, Silvestro Micera of the Swiss Federal Institute of Technology in Lausanne presented the latest version of a prosthetic hand that can provide real-time sensory feedback, enabling its user to carefully control grasp.
The prototype version of this bionic hand had only two broad areas that provided sensory feedback. The latest version gives feedback to the user from individual fingertips as well as the palm and wrists, giving people a more lifelike experience.