A patient operating a mind-controlled prosthetic hand has been able to move individual fingers for the first time, in an experiment carried out by John Hopkins University researchers.
The experiment, described in the latest issue of the Journal of Neural Engineering, has been hailed as a potential breakthrough in restoring fine motor skills in amputees.
"We believe this is the first time a person using a mind-controlled prosthesis has immediately performed individual digit movements without extensive training," said Nathan Crone, professor of neurology at the Johns Hopkins University School of Medicine who oversaw the study.
"This technology goes beyond available prostheses, in which the artificial digits, or fingers, move as a single unit to make a grabbing motion, like one used to grip a tennis ball."
The subject of the experiment was a young epilepsy sufferer, not an actual amputee. The scientists chose to work with this subject as he was already scheduled to undergo surgery that would allow his doctors to monitor the origins of seizures in his brain. During the surgery, an array of 128 electrode sensors embedded in a rectangular sheet of film the size of a credit card was placed on the part of the man's brain that normally controls hand and arm movements.
The researchers then instructed the man to move each finger separately and monitored which part of the brain lit up.
The method, in reverse, was subsequently used to control the fingers of the artificial hand.
"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 Guy Hotson, graduate student and lead author of the study. "This precision is what allowed us to separate the control of individual fingers."
Initially, the mind-controlled limb had an accuracy of 76 per cent. Once the researchers coupled the ring finger and the little finger, the accuracy increased to 88 per cent.
"The part of the brain that controls the little and ring fingers overlaps and most people move the two fingers together," says Crone. "It makes sense that coupling these two fingers improved the accuracy."
In addition to collecting data on the parts of the brain involved in motor movement, the researchers measured electrical brain activity involved in tactile sensation. To do this, the subject was fitted with a glove with small, vibrating buzzers in the fingertips, which went off individually in each finger. The researchers measured the resulting electrical activity in the brain for each finger connection.
The test subject didn’t receive any training ahead of the two-hour experiment.