Bidirectional brain signals sense and move virtual objects
October 6, 2011
“Someday in the near future, quadriplegic patients will take advantage of this technology not only to move their arms and hands and to walk again, but also to sense the texture of objects placed in their hands, or experience the nuances of the terrain on which they stroll with the help of a wearable robotic exoskeleton,” said study leader Miguel Nicolelis, MD, PhD, professor of neurobiology at Duke University Medical Center and co-director of the Duke Center for Neuroengineering.
Sensing textures of virtual objects
Without moving any part of their real bodies, the monkeys used their electrical brain activity to direct the virtual hands of an avatar to the surface of virtual objects and differentiate their textures. Although the virtual objects employed in this study were visually identical, they were designed to have different artificial textures that could only be detected if the animals explored them with virtual hands controlled directly by their brain’s electrical activity.
The texture of the virtual objects was expressed as a pattern of electrical signals transmitted to the monkeys’ brains. Three different electrical patterns corresponded to each of three different object textures.
Because no part of the animal’s real body was involved in the operation of this brain-machine-brain interface, these experiments suggest that in the future, patients who were severely paralyzed due to a spinal cord lesion may take advantage of this technology to regain mobility and also to have their sense of touch restored, said Nicolelis.
First bidirectional link between brain and virtual body
“This is the first demonstration of a brain-machine-brain interface (BMBI) that establishes a direct, bidirectional link between a brain and a virtual body,” Nicolelis said.
“In this BMBI, the virtual body is controlled directly by the animal’s brain activity, while its virtual hand generates tactile feedback information that is signaled via direct electrical microstimulation of another region of the animal’s cortex. We hope that in the next few years this technology could help to restore a more autonomous life to many patients who are currently locked in without being able to move or experience any tactile sensation of the surrounding world,” Nicolelis said.
“This is also the first time we’ve observed a brain controlling a virtual arm that explores objects while the brain simultaneously receives electrical feedback signals that describe the fine texture of objects ‘touched’ by the monkey’s newly acquired virtual hand.
“Such an interaction between the brain and a virtual avatar was totally independent of the animal’s real body, because the animals did not move their real arms and hands, nor did they use their real skin to touch the objects and identify their texture. It’s almost like creating a new sensory channel through which the brain can resume processing information that cannot reach it anymore through the real body and peripheral nerves.”
The combined electrical activity of populations of 50 to 200 neurons in the monkey’s motor cortex controlled the steering of the avatar arm, while thousands of neurons in the primary tactile cortex were simultaneously receiving continuous electrical feedback from the virtual hand’s palm that let the monkey discriminate between objects, based on their texture alone.
Robotic exoskeleton for paralyzed patients
“The remarkable success with non-human primates is what makes us believe that humans could accomplish the same task much more easily in the near future,” Nicolelis said.
The findings provide further evidence that it may be possible to create a robotic exoskeleton that severely paralyzed patients could wear in order to explore and receive feedback from the outside world, Nicolelis said. The exoskeleton would be directly controlled by the patient’s voluntary brain activity to allow the patient to move autonomously. Simultaneously, sensors distributed across the exoskeleton would generate the type of tactile feedback needed for the patient’s brain to identify the texture, shape and temperature of objects, as well as many features of the surface upon which they walk.
This overall therapeutic approach is the one chosen by the Walk Again Project, an international, non-profit consortium, established by a team of Brazilian, American, Swiss, and German scientists, which aims at restoring full-body mobility to quadriplegic patients through a brain-machine-brain interface implemented in conjunction with a full-body robotic exoskeleton.
The international scientific team recently proposed to carry out its first public demonstration of such an autonomous exoskeleton during the opening game of the 2014 FIFA Soccer World Cup that will be held in Brazil.
Ref.: Joseph E. O’Doherty, Mikhail A. Lebedev, Peter J. Ifft, Katie Z. Zhuang, Solaiman Shokur, Hannes Bleuler, and Miguel A. L. Nicolelis, Active tactile exploration using a brain–machine–brain interface, Nature, October 2011 [doi:10.1038/nature10489]