This illustration shows the electrode array on the subject’s brain, including a representation of what part of the brain controls each finger. Illustration courtesy of Guy Hotson.
Physicians and biomedical engineers from Johns Hopkins University (JHU) have reported what they believe is the first successful effort to wiggle artificial fingers individually and independently of each other using a mind-controlled robotic arm to control the movement. The proof-of-concept feat, described online February 10 in the Journal of Neural Engineering, represents a potential advance in technologies to restore refined hand function to those who have lost arms to injury or disease, the researchers said.
“We believe this is the first time a person using a mind-controlled prosthesis has immediately performed individual digit movements without extensive training,” said senior author Nathan Crone, MD, professor of neurology at the JHU School of Medicine. “This technology goes beyond available prostheses, in which the artificial digits, or fingers, moved as a single unit to make a grabbing motion, like one used to grip a tennis ball.”
For the experiment, the research team recruited a young man with epilepsy who was already scheduled to undergo brain mapping at The Johns Hopkins Hospital’s Epilepsy Monitoring Unit, Baltimore, to pinpoint the origin of his seizures. The subject was not missing an arm or hand; he was outfitted with a device that essentially took advantage of a brain-mapping procedure to bypass control of his own arm and hand. While brain recordings were made using electrodes surgically implanted for clinical reasons, the signals also controlled the Modular Prosthetic Limb developed by the JHU Applied Physics Laboratory.
Prior to connecting the prosthesis, the researchers mapped and tracked the specific parts of the subject’s brain responsible for moving each finger, then programmed the prosthesis to move the corresponding finger. First, the patient’s neurosurgeon placed an array of 128 electrode sensors-all on a single rectangular sheet of film the size of a credit card-on the part of the man’s brain that normally controls hand and arm movements. Each sensor measured a circle of brain tissue 1mm in diameter. The computer program the JHU team developed had the man move individual fingers on command and recorded which parts of the brain “lit up” when each sensor detected an electric signal. The researchers also measured electrical brain activity involved in tactile sensation. To do this, the subject was outfitted with a glove with small, vibrating buzzers in the fingertips that went off individually. The researchers measured the resulting electrical activity in the brain for each finger connection.
After the motor and sensory data were collected, the researchers programmed the prosthetic arm to move corresponding fingers based on which part of the brain was active. The researchers turned on the prosthetic arm, which was wired to the patient through the brain electrodes, and asked him to think about moving each finger individually. The electrical activity generated in the brain moved the fingers.
Initially, the mind-controlled limb had an accuracy of 76 percent. Once the researchers coupled the ring and pinkie fingers together, the accuracy increased to 88 percent because the part of the brain that controls the pinkie and ring fingers overlaps. The researchers noted there was no pretraining required for the subject to gain this level of control, and the entire experiment took less than two hours.
Crone cautioned that application of this technology to those missing limbs is still some years off and will be costly, requiring extensive mapping and computer programming.
Editor’s note: This story was adapted from materials provided by the Johns Hopkins University School of Medicine.
