A paralysed woman was still able to accurately control a computer cursor with her thoughts 1000 days after having a tiny electronic device implanted in her brain, say the researchers who devised the system. The achievement demonstrates the longevity of brain-machine implants.
The woman, for whom the researchers use the pseudonym S3, had a brainstem stroke in the mid-1990s that caused tetraplegia – paralysis of all four limbs and the vocal cords.
In 2005, researchers from Brown University in Providence, Rhode Island, the Providence VA Medical Center and Massachusetts General Hospital in Boston implanted a tiny silicon electrode array the size of a small aspirin into S3’s brain to help her communicate better with the outside world.
The electrode array is part of the team’s BrainGate system, which includes a combination of hardware and software that directly senses the electrical signals produced by neurons in the brain which control the planning of movement.
The electrode decodes these signals to allow people with paralysis to control external devices such as computers, wheelchairs and bionic limbs.
In a study just published, the researchers say that in 2008 – 1000 days after implantation – S3 proved the durability of the device by performing two different «point-and-click» tasks by thinking about moving a cursor with her hand.
Her first task was to move a cursor on a computer screen to targets arranged in a circle and select each one in turn. The second required her to follow and click on a target as it moved around the screen in varying sizes.
This proof of concept – that after 1000 days a woman who has no functional use of her limbs and is unable to speak can reliably control a cursor on a computer screen using only the intended movement of her hand – is an important step for the field
However, the device did not perform perfectly – fewer electrodes were recording useful neural signals than they did when tested six months after implantation.
The researchers say there is no evidence of any fundamental incompatibility between the sensor and the brain. Instead, they believe the decreased signal quality over time can largely be attributed to engineering issues. Ongoing research means these issues are now less of a problem than they were when S3 received her implant.
Our objective with the neural interface is to reach the level of performance of a person without a disability using a mouse
Hochberg says that S3’s implant is still working and she is still participating in trials.