“You’re trying to disrupt abnormal information flow and minimally disrupt normal information flow,” says Kelly Foote, M.D., a neurosurgeon at the University of Florida College of Medicine who specializes in DBS.

Researchers are also trying to make DBS implants more efficient. Currently, dialing in the exact intensity and frequency of pulses is a trial-and-error process — and it’s one that needs to be adjusted as the disease worsens. Ideally, “the device could just program itself and turn itself on and off or up and down to meet the needs of that patient,” Foote says.

We’re not there yet, but research on such an adaptive device — known as a “closed loop” device — is well underway for people with both essential tremor and Parkinson’s disease.

We’re not just seeing advancements in well-established brain implants. Here’s a look at new technologies that could one day change the way we treat a number of health issues.  

Recovering movement

One of the leading groups in this space is Switzerland’s NeuroRestore research center. In a NeuroRestore study published last May in the journal Nature, a team led by Lausanne University neurosurgeon Jocelyne Bloch and Grégoire Courtine of the Swiss Federal Institute of Technology Lausanne unveiled a closed-loop “digital bridge” that could reconnect the brain and spinal cord after an injury had severed them. 

In a small-scale human clinical trial, the researchers worked with Gert-Jan Oskam, a 40-year-old Dutch man who was told he would never walk again after breaking his neck in a cycling accident in 2011. The team implanted 64 electrodes over the surface of Oskam’s motor cortex, the brain region responsible for controlling his movement.

These electrodes sensed Oskam’s brain activity and then sent those signals to a computer that parsed out Oskam’s movement intentions. These signals, in turn, were sent to a pulse generator that sent electrical pulses into a 16-electrode lead implanted beside Oskam’s spinal cord. In effect, these pulses mimicked signals that Oskam’s brain would have sent down the spine before his injury cut the connection. The system can detect a movement that Oskam is trying to make and then quickly transmit that signal to his spine. Combined with regular physical therapy, the system let Oskam walk with crutches and a walker-like device. And over a three-year period, Oskam’s consistent use of the system improved his neurological recovery: He can now walk independently for short distances with crutches, without needing to use the system.

“Honestly, I can tell you, I think this is the most impressive thing I’ve ever seen,” says NeuroRestore member Eduardo Martin Moraud, a clinical neuroscientist at the University Hospital in Lausanne.  

The NeuroRestore group has also been working on treatments for Parkinson’s disease. People with Parkinson’s can be prone to falls and what’s known as freezing gait: a sudden stopping of movement or inability to move, especially when approaching a doorway. In a study published in November 2023 in the journal Nature Medicine, Moraud and colleagues unveiled a system that uses a spinal implant in concert with four inertial sensors — like the ones that detect when a smartphone is tilted at an angle — to correct the walking gait of a person with Parkinson’s.

Unlike DBS, which adds electrical “white noise” to the brain, this system predicts which kinds of signals ought to be reaching the spine and sends those out into the spinal cord.

This system uses a sophisticated model of how nerve signals activate the body’s muscles to automatically correlate the person’s gait with the nerve signals that the brain should be sending to the legs. It then sends corrective pulses of electricity to electrodes surgically implanted next to the spinal cord. When using the implant in combination with three months of physical therapy, the study’s main test subject — a man from Bordeaux, France, named Marc Gauthier, who was 62 at the time of the study — saw his freezing gait almost vanish and the overall quality of his walking gait improve.

Gauthier has been using the device for roughly three years, for about eight hours per day. He now takes miles-long nature walks around a lake. “I can walk better, I am less unbalanced, and I think that stairs don’t scare me anymore,” he said in patient testimony included with the 2023 study. “Now, I can walk five kilometers without any stops.”

Restoring speech

Other research teams are working to restore speech in people who have lost it. Two studies published side-by-side in Nature in August 2023 unveiled brain implants that could synthesize speech from recordings of brain activity. Working at between 60 and 70 words per minute, these systems are currently about half as fast as natural conversation — but they are more than three times as fast as similar systems that came before them.

One of these systems, developed by a team led by University of California, San Francisco neurosurgeon Edward Chang, M.D., even came up with a way to use brain activity to animate a digital avatar. This study’s participant, a 48-year-old woman named Ann Johnson, suffered a stroke in her brain stem in 2005 and was left paralyzed and unable to speak. The system could decode Johnson’s brain activity and decipher her intentions to move her facial muscles and vocal tract — and then translate these signals into synthetic speech and corresponding animations of a digital face.
 

In part, this study depended on electrodes implanted onto the upper surface of Johnson’s brain. There are inherent tradeoffs to these arrays, which have been around for years, but like DBS, these technologies are being improved and refined. Implanting them in the brain improves signal quality — meaning that they can record brain signals in greater detail — but it also increases the risk of infection.

Implanted devices must also resist corrosion, and then there’s the challenge of outwitting the body’s natural immune response, which may recognize the implant as a foreign substance and surround it with scar tissue, worsening its performance. “Making these things stable over time is very difficult,” Moraud says. “After a year, maybe you don’t even sense anything anymore.”

Companies are trying to get around these issues by working with substances that are less likely to break down in the brain, for example, or making their electrodes extremely thin to minimize risk of tissue damage. Neuralink’s “threads” of electrodes are between 4 and 6 microns thick — about 5 percent the thickness of a sheet of printer paper.

Even still, the technology needs tweaks. In the case of Neuralink’s first trial participant, 85 percent of the implant’s 64 threads stopped working several weeks after surgery, after many of the threads had retracted out of the brain tissue. The company says it has since stabilized these threads and the study participant is back to being able to use his implant to control his computer. In its August update, Neuralink reported that it had not seen any threads retract from the second participant’s brain tissue.