The brain implant is a small array that’s four millimeters on each side (“about the size of a baby aspirin,” says Donoghue) with 96 hairlike electrodes extending from one side. The device sits on the surface of the brain, and the electrodes penetrate the arm-controlling region of the motor cortex by one millimeter.
The implant records the impulses of dozens of neurons. A patient’s intent to move generates these impulses, which are then transmitted to a computer that translates the patterns of electrical activity into commands that can control a robotic arm.
"What’s striking to me about this study is that it’s nicely showing, for the first time in human patients, that you can use these signals to control a robot of importance for activities of daily living for a patient," says Andrew Jackson, a neuroscientist at Newcastle University.
The researchers say that algorithmic improvements in picking up patterns of activity in the brain and interpreting those patterns were key to the advance.
The goal of the pilot clinical trial is to develop technologies that can restore the ability to communicate and move and to give independence to people with neurological disease or injury. So far, seven patients have enrolled in the trial. The two participants in this latest work both suffered from brain-stem strokes that left them unable to speak or move their limbs. At the time of the study, one patient had the implant for five months, the other for more than five years.
The longevity of the implants demonstrates that the device can pick up usable signals from the brain for years, a point of concern in the field. “When you put something into the brain, there’s a reaction to the presence of that device,” says Donoghue. Cells are damaged or displaced by the electrodes, and the brain can form scar tissue around them. But “it doesn’t seem that the reaction of the brain is a barrier to recording,” says Donoghue.