A mind-controlled prosthetic arm developed by Johns Hopkins researchers allows wearers to move individual digits independently of each other. The proof-of-concept device represents an advance in technologies to restore refined hand function to those who have lost arms to injury or disease, say the physicians and biomedical engineers.

For the experiment, the research team recruited a young man with epilepsy already scheduled to undergo brain mapping at The Johns Hopkins Hospital’s Epilepsy Monitoring Unit to pinpoint the origin of his seizures.

While brain recordings were made using electrodes surgically implanted for clinical reasons, the signals also controlled a modular prosthetic limb developed by the Johns Hopkins University 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 1 millimeter in diameter.

The Johns Hopkins researchers had the man move individual fingers on command, recording which parts of the brain “lit up” when each sensor detected an electric signal.

To measure the electrical brain activity involved in tactile sensation, the subject was outfitted with a glove with small, vibrating buzzers in the fingertips, which initiated individually in each finger. 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 the subject to “think” about individually moving thumb, index, middle, ring and pinkie fingers. The electrical activity generated in the brain moved the fingers.

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