Elon Musk's company Neuralink gave one to a second person Brain-Computer Interface (BCI) and could implant eight more of these devices this year, Musk said.

In a published on August 2nd 8 hour podcast Musk said that the second implant works well and that about 400 of its 1,042 electrodes provide signals from the recipient's brain. Musk did not reveal any details about the implant surgery or the recipient, other than that the person has a spinal cord injury, as does Noland Arbaugh, the first recipient of a Neuralink BCI.

Now scientists are waiting to see whether the Fremont, California-based company can avoid the mechanical difficulties that plagued the implantation of its first device in January.

“This is a necessary advance,” says Sameer Sheth, a neurosurgeon and neurotechnology researcher at Baylor College of Medicine in Houston, Texas. "I really hope they can continue doing this safely. They have a lot to contribute to human health and disease."

Anchored in the skull

The BCI developed by Neuralink, called Telepathy, is the third commercial BCI implantation to enter long-term human trials. The others use electrode arrays that are either attached to the inside of a cerebral blood vessel or sit directly on the brain. Telepathy instead has an electronics hub about the size of a coin that is placed in a hole made in the recipient's skull. From this hub, 64 flexible threads run through the fluids and membranes around the brain and into the recipient's cortex.

A surgical robot developed by Neuralink inserts these threads into the motor cortex, the area of ​​the brain that controls movement. This process takes 20 to 40 minutes, said Dongjin Seo, co-founder and president of Neuralink, on the podcast. Each thread has 16 recording sites, a total of 1,024 electrodes that can potentially record neural activity and send signals to an external device via Bluetooth.

The first person to receive a Neuralink BCI was Noland Arbaugh from Yuma, Arizona, who was paralyzed from the neck down after a diving accident in 2016. He can now use the device to control a cursor on a computer screen, for example to play games.

But a month after Arbaugh's BCI was implanted, 85% of its flexible filaments that record neural activity have withdrawn from his brain. This affected the performance of the device, which was “really, really hard” for Arbaugh. “It would have been a cruel twist of fate if I could have seen the view from the top of that mountain and then everything fell apart after a month,” Arbaugh said on the podcast.

Neuralink engineers responded by changing the recording algorithm that converts neural data into commands that are transmitted to the computer. The original algorithm recorded the activity of individual neurons, but the revised version records the average activity of neurons near each electrode. Although the average signals have less resolution, the effects were immediate.

“Why do we take this risk and implant so many threads when it works quite well and gets better with fewer threads?” Sheth wonders.

In a live stream on X on July 10, Matthew MacDougall, head of neurosurgery at Neuralink, said the initial surgical procedure caused an air pocket that may have later dislodged the electrodes. He said that when placing the second implant, the surgical team would try to avoid such air pockets and redesign the hole to place the hub deeper into the skull and thread the flexible electrodes deeper into the cortex.

"It's not common" to make so many changes in the BCI implantation process between recipients, Sheth says. "But I think it's good that you learn from the first one and then really make the second one better."

Questions about stability

Still, Vikash Gilja, chief scientific officer at Paradromics, a competitor to BCI based in Austin, Texas, says questions about the device's stability and durability need to be answered.

The brain, says Gilja, “doesn’t just lie static relative to the skull”: it moves when a person breathes and moves. It's not clear whether this slight but continuous movement will negatively affect the electrode threads that run from the skull through the meninges to the brain, Gilja says.

The long-term stability of the materials that make up Neuralink’s electrodes is another unknown. Other BCI implants use different types of metallic electrodes with established longevity records. “You only understand the time constants when you are in the human body,” says Gilja. Devices, he says, need to be studied over years, not months.

Long term plans

Musk said during the July 10 livestream that Neuralink plans to regularly offer improved devices, each of which would be implanted during further neurosurgery. In contrast, Paradromics calls for “as much time as possible between consecutive neurosurgery procedures,” says Gilja.

Musk said on the podcast that Neuralink's ultimate goal is one BCI is what enables people to have a symbiosis with artificial intelligence to enter. He predicted that future BCIs will help people with psychosis, seizures and memory loss.

Sheth says treating such conditions is much more challenging than moving computer cursors, adding that human augmentation requires careful discussion.

More immediately, Anna Wexler, a neuroethicist at the University of Pennsylvania in Philadelphia, says these predictions could mislead potential study participants. “It certainly raises questions about what draws these people to the studies and what they understand about what they are getting into.”