Mind-controlled prosthetic arm enters the 'digital' age

By John Murphy, MDLinx
Published February 16, 2016

Key Takeaways

Researchers have demonstrated, for the first time, a mind-controlled interface that moves individual fingers on a prosthetic hand. To achieve this, the researchers mapped cortical areas of the brain responsible for specific finger control, according to a study published online in Journal of Neural Engineering.        

Until now, prostheses have not been able to move individual fingers independently or with this much dexterity.

“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 Johns Hopkins University School of Medicine, in Baltimore MD. “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,” Dr. Crone said.

This proof-of-concept achievement could lead to a technological advance for restoring motor skills in people who have lost arms to injury or disease, the researchers predicted.

For this experiment, the researchers recruited 20-year-old man with epilepsy who was already undergoing brain mapping (at The Johns Hopkins Hospital’s Epilepsy Monitoring Unit) to localize the origin of his seizures. The patient’s neurosurgeon placed an array of 128 subdural electrodes—all on a single rectangular sheet of film the size of a credit card—over sensorimotor regions controlling the man’s hand and arm movements.

After collecting data to track the specific areas of the brain involved in motor movement, the researchers performed a series of experiments. The first test measured electrical brain activity involved in tactile sensation. To do this, the researchers outfitted the subject with a glove implanted with small, vibrating buzzers in the fingertips, which went off individually in each finger. When the buzzers went off, the researchers measured the resulting somatosensory feedback in the brain for each finger connection. 

In the second experiment, the subject tapped his fingers on a surface—movements that were used to train the system to recognize cortical activation. 

Following these initial tests, the researchers programmed the prosthetic arm to move its fingers corresponding to the subject’s neural data, and then wired the prosthetic arm to the brain-machine interface attached to the subject’s electrodes. The researchers then asked the subject to “think” about individually moving thumb, index, middle, ring, and pinkie fingers.

The electrical activity generated in the subject’s brain moved the fingers on the prosthesis in real time.

“Our approach of using the native functional anatomy of sensorimotor cortex obviates the need for operant conditioning, potentially providing immediate intuitive control to patients that can be expanded to a large number of degrees of freedom without placing significant cognitive burden on the patient,” the researchers wrote in their paper.

The electrode array on the subject’s brain, with a representation of what part of the brain controls each finger. (Image: Guy Hotson)“The electrodes used to measure brain activity in this study gave us better resolution of a large region of cortex than anything we’ve used before and allowed for more precise spatial mapping in the brain,” said the study’s lead author Guy Hotson, a PhD student in Dr. Crone’s lab. “This precision is what allowed us to separate the control of individual fingers.”

The mind-controlled fingers initially moved with 76% accuracy. Once the researchers coupled the ring and pinkie fingers together, the accuracy increased to 88%. “The part of the brain that controls the pinkie and ring fingers overlaps, and most people move the two fingers together,” Dr. Crone said. “It makes sense that coupling these two fingers improved the accuracy.”

Application of this technology to real-life use in people with missing limbs will be costly and is still years away, requiring extensive mapping and computer programming, Dr. Crone cautioned.

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