As with most of biology’s wonders, we take our coordination for granted. We see something we want; we reach out and grab it. Even if the desired object is moving, like a glass of champagne on the tray of a passing waiter. How do our brains do it?
Our brains analyze the visual target (the approaching glass), make an estimate of its velocity, and send a signal to the arm and hand to reach out and grasp. The grasping has to be timed precisely, and the hand has to open the right amount. We use a different grasping motion for a wine glass than for a beer mug.
Amazingly, scientists now know enough about these brain signals to tap into them and use them to control artificial limbs.
A team of scientists headed by Andrew Schwartz at the
The monkeys were first trained to control the prosthetic arm using a joystick. The arm had 6 degrees of freedom; three at the shoulder, one at the elbow, and one at the hand.
Once they got the feel for the arm, the monkeys were implanted with electrode arrays situated on the part of the brain that controls arm and hand movement. The prosthetic arm was hooked up to the monkey and controlled by the signals recorded from the electrodes.
After several weeks of training, the monkeys were able to grasp bits of food held out to them by a researcher, and put the food into their mouths. The monkeys’ arms were restrained to keep them from grabbing the food with their own hands.
The monkeys got very comfortable eating with the prosthetic limb. They even licked their prosthetic fingers when bits of marshmallow stuck to them. There are some nice videos of the monkeys in action here.
Prosthetics which are controlled by nerve signals already exist for humans, but they intercept the nerve signals at the shoulder. They’re great for patients with amputated arms, and they’ve made remarkable progress, allowing users to grasp objects and move individual fingers.
Brain-computer interfaces exist for patients with locked-in syndrome, which is a syndrome in which patients are awake and aware, but cannot move or communicate. Generally, these interfaces allow patients to move a cursor on a computer screen, and thus communicate with the outside world.
Tapping brain signals to control prosthetic limbs will someday help paralyzed patients to regain movement.