Major advances in neuroscience could lead to a wider range of brain-controlled prosthetic limbs that can restore mobility for people. A joint US-Portuguese study has paved the way for development of thought-controlled ‘neuroprosthetic’ devices to help people cope with spinal cord injuries, amputation and other disabilities.
Dr Jose Carmena of UC Berkeley hopes that his team’s insights into the brain’s wiring will lead to a wider range of more natural prostheses. “[The research] suggests that learning to control a brain-machine interface (BMI), which is inherently unnatural, may feel completely normal to a person, because this learning is using the brain’s existing built-in circuits for natural motor control.”
Earlier studies did not rule out the role of an individual’s physical movement when learning to use a prosthetic device: a key issue for people unable to move, according to Dr Carmena. “Most brain-machine interface studies have been done in healthy, able-bodied animals. What our study shows is that neuroprosthetic control is possible, even if physical movement is not involved.”
Devising an experiment where rats could only complete abstract tasks if overt physical movement was not involved, the researchers decoupled the role of the targeted motor neurons they used to twitch their whiskers with the action needed to be rewarded with food.
A brain-machine interface that converted brain waves into auditory tones was fitted to the rats. To gain their reward, the rats had to modulate their thought patterns within a specific brain circuit, raising or lowering the signal’s pitch.
The rats received auditory feedback, enabling them to associate pitch with specific thought patterns. After a fortnight, the rats had learnt to produce a high-pitched tone for food pellets and a low-pitched one for sugar water.
This is unnatural in rats, according to the study’s co-principal Dr Rui Costa. “This tells us that it’s possible to craft a prosthesis in ways that do not have to mimic the anatomy of the natural motor system in order to work.”
“The rats were aware; they knew that controlling the pitch of the tone was what gave them the reward, so they controlled how much sugar water or how many pellets to take, when to do it, and how to do it in absence of any physical movement,” said Dr Costa.
Dr Carmena hopes his team’s findings will lead to new, more naturalistic prosthetic devices, concluding: “We don’t want people to have to think too hard to move a robotic arm with their brain.”