The new work shows that it’ll possible to restore voluntary movement and hand function in humans with spinal cord injuries with further advance in the field of neuroprosthetics.
To restore communication between the brain and the muscles that move limbs, a team led by Lee Miller of the Northwestern University turned to a method called brain-controlled functional electrical stimulation (FES).
- They trained 2 monkeys to pick up and move rubber balls, rewarding them with juice when they dropped the ball into a chute.
- They implanted electrodes into their primary motor cortex, the part of the brain that controls the hand.
- They also implanted up to 5 electrodes in 3 of the monkeys’ arm muscles.
- The implants allowed them to record the electrical activity of about 100 neurons. By recording simultaneously from the brain and muscle electrodes as the monkeys gripped objects, the researchers developed computerized decoding algorithms that predicted how signals from the brain translated into electrical activity in each of the 3 muscles.
- Then they injected a local anesthetic to block certain nerves at the elbow to temporarily simulate the effects of paralysis. The monkeys were unable to grasp the ball, but their neurons kept firing in a similar way to their previous attempts.
- Then the team stimulated the electrodes in the muscles, bypassing the monkeys’ spinal cord.
- With voluntary control of their paralyzed muscles restored, the monkeys performed their task despite the complete paralysis of muscles in their forearm and hand.
The monkeys succeeded about 80% of the time.
Watch the video of a monkey performing the task.
"What's fundamentally different about our system is that we're going back to the brain and eavesdropping on the signals that normally occur," Miller says. He hopes this type of neuroprosthesis will eventually enable paralyzed humans to move a hand just by thinking about it.
He adds: "By going directly to the brain, we have potential access to a much richer set of control signals that represent the actual movement the patient is attempting to make."
The work was published in Nature this week.
Image from Ethier et al., Nature