Typing six words per minute may not sound very impressive. But for paralyzed people typing via a brain-computer interface (BCI), it’s a new world record.

To pull off this feat, two paralyzed people used prosthetics implanted in their brains to control computer cursors with unprecedented accuracy and speed. The experiment, reported today in Nature Medicine, was the latest from a team testing a neural system called BrainGate2. While this implant is only approved for experiments right now, researchers say this demonstration proves that such technology can be truly useful to quadriplegics, and points the way toward regular at-home use.

The two people who volunteered for this study have amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, a degenerative neural disorder that leads to complete paralysis. Lead researcher Jaimie Henderson, co-director of Stanford’s Neural Prosthetics Translational Lab, calls it a “humbling experience” to work with quadriplegic patients who willingly undergo brain surgery and devote themselves to science experiments that will push forward this early-stage technology. “They’ve become true partners with us in this endeavor,” Henderson says.

The BrainGate2 system consists of an array of minuscule electrodes implanted, in this case, in a region of the motor cortex known as the “hand knob.” The electrodes record the patterns of electrical activity in the neurons there, which fire when the person either moves or imagines moving their hand. The BrainGate2 system also includes decoding software, which turns a messy signal into a clear command for an external device—in this case, a computer cursor. Other experiments have used BCIs to control robotic arms, and they could theoretically be used to control wheelchairs, cars, or anything else that can be moved by remote control.

In this study’s first task, the participants repeatedly moved their cursors to targets on a computer screen (see video below), which they...

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