Controlling neuroprosthetics with your mind

March 6, 2012

Perfcct pitch: brain waves from the rodent primary motor cortex are compared to the audible target (high or low) pitch (frequency), giving the rodent a food reward when the target pitch is achieved (credit: Aaron C. Koralek et al./Nature)

Neuroscientists have found that the brain is more flexible and trainable than previously thought, opening the door to development of thought-controlled prosthetic devices to help people with spinal cord injuries, amputations and other impairments.

The new study, by neuroscientists at the University of California, Berkeley, and the Champalimaud Center for the Unknown in Portugal, shows that through a process called plasticity, parts of the brain can be trained to do something they normally do not do.

Brain-controlled prosthetics

Researchers have found that the same brain circuits use in learning motor skills, such as riding a bike or driving a car, can be used to master purely mental tasks, even arbitrary ones. The study advances work by researchers who have been studying the brain circuits used in natural movement, to mimic them for the development of prosthetic devices.

“What we hope is that our new insights into the brain’s wiring will lead to a wider range of better prostheses that feel as close to natural as possible,” said Jose Carmena, UC Berkeley associate professor of electrical engineering, cognitive science and neuroscience. The insights suggest that “learning to control a BMI (brain-machine interface), 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.”

“This is key for people who can’t move,” said Carmena, who is also co-director of the UC Berkeley-UCSF Center for Neural Engineering and Prostheses. “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.”

Unnatural thoughts

To clarify these issues, the scientists set up a clever experiment in which rats could only complete an abstract task if overt physical movement was not involved. The researchers decoupled the role of the targeted motor neurons needed for whisker twitching from the action necessary to get a food reward.

The rats were fitted with a brain-machine interface that converted EEG brain waves into auditory tones. To get the food reward — either sugar-water or pellets — the rats had to modulate their thought patterns  (not their movements) within a specific brain circuit in order to raise or lower the pitch of the signal.

Auditory feedback was given to the rats so that they learned to associate specific thought patterns with a specific pitch. Over a period of just two weeks, the rats quickly learned that to get food pellets, they would have to create a high-pitched tone, and to get sugar water, they needed to create a low-pitched tone.

If the group of neurons in the task were used for their typical function — whisker twitching — there would be no pitch change to the auditory tone, and no food reward.

“This is something that is not natural for the rats,” said 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 study was also set up in a way that demonstrated intentional, as opposed to habitual, behavior. The rats were able to vary the amount of pellets or sugar water received based upon their own level of hunger or thirst.

“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 Costa.

Researchers hope these findings will lead to a new generation of prosthetic devices that feel natural.

“We don’t want people to have to think too hard to move a robotic arm with their brain,” said Carmena.

Ref.: Aaron C. Koralek et al., Corticostriatal plasticity is necessary for learning intentional neuroprosthetic skills, Nature, 2012 [DOI: 10.1038/nature10845]

See also: Better neural control of prosthetics for amputees