Here’s our summary of what’s new about Neuralink, and what isn’t.

Overall idea: Not new. Scientists have been testing brain implants on patients that allow them to move computer cursors or robot arms for about 15 years, but only in research settings.

Design approach: What Neuralink is trying to do now is to engineer a safe, miniaturized interface that's actually practical to have inside your head. “Conceptually that’s great; we need to get the brain control stuff out of the lab and turn it into a commodity,” says Andrew Schwartz, a brain-interface researcher at the University of Pittsburgh. Schwartz has previously worked with two paralyzed people in his lab and allowed them to control a dexterous robotic arm with their minds. But the experimental set-up is so complicated (including a fat wire that gets plugged into patients' heads) the subjects can’t take it home. He says Neuralink appears to be working on the right engineering questions to make a more useful brain implant, though Schwartz adds that “I don’t know is how much of it is real.”

The processor: Musk and company showed off a miniature, dedicated computer chip whose job it is to turn the electrical noise from neurons into crisp digital signals. The chip does only one thing—like those used by Bitcoin miners—and does it using as little energy as possible, which is necessary if it’s going to sit under your skull. “You need to not change your batteries out every two hours,” says Andrew Hires, an assistant professor of biological sciences at the University of Southern California. Hires says Neuralink “has taken a bunch of cutting-edge stuff and put it together” in ways that academic teams have struggled to do. Still missing from Neuralink’s demo is a wireless transmitter, which other companies have demonstrated.

At left, thread-like electrodes in the brain of an animal are able to record neurons. On the right, a rat wears a computer chip with a USB plug. Neuralink

The electrodes: Neuralink talked up thin, flexible, polymer wires that it wants to poke into peoples’ brains through holes in their skulls. The flexible electrodes are similar to technologies being developed elsewhere (including by Chong Xie at the University of Texas, Austin). “That is about the state of the art, but not past it,” says Hires.

Neuralink claims that it recorded from 1,000 or so neurons in a rat. But don't be too impressed by the big number. It isn't record-breaking, and may not even be necessary to capture brain signals needed for the applications Neuralink is looking at. Recording just 30 neurons in the motor cortex of a volunteer’s brain as they imagine moving their arm is enough to allow them to control a computer cursor on a screen.

Longevity: How long will an implant last? This could be the bugbear for Neuralink. While thin, flexible electrodes could last longer and cause less damage, reliability is a serious problem inside the brain, and electrodes cause tissue damage called gliosis. According to a tweet thread by Jacob Robinson, a professor at Rice University, Musk himself said the problem is “definitely not solved.” Robinson noted that it’s hard to speed up testing in animals of how long different electrode materials perform. Time doesn’t pass faster, even for billionaires.

The sewing robot: Neuralink says it developed a neurosurgery robot that automatically inserts the fine electrode threads into the brain at precise locations, avoiding blood vessels, at a rate of six per minute. “It’s a cool robot, and it took a lot of work,” says Schwartz. “But did it require a new invention, like a transistor? The answer is no.” Yesterday, the defense funding agency, DARPA, sniffed on twitter that they had funded the initial development of the sewing robot that Neuralink presented as its own idea.