Brain-computer interface trials gain momentum

Casey Harrell, a man with ALS, is considered the 'first power user' of a brain implant by researchers who worked with him. Harrell is paralyzed and unable to speak coherently without the device. He has now spent almost three years using a brain-computer interface (BCI) that enables him to 'speak,' surf the web, and perform his job as a climate activist, largely independently.

Since Harrell was implanted with the device in July 2023, a team at the University of California, Davis, has worked with him to adjust and improve its offerings. They've refined its accuracy and introduced settings including a privacy mode and a 'profanity filter' that lets Harrell talk to his daughter without risking accidental swearing. Harrell told me that, for him, the device is 'nothing short of revolutionary!' It has enabled him to maintain an income, reconnect with friends and family, and read to his daughter.

The team that developed his BCI is one of several working on ways to use technology to allow people with paralysis to communicate, engage with the online world, and regain some independence. And Harrell is one of a growing number of people volunteering their brains to, as he puts it, 'pay it forward and do the scientific research … [and] get some personal benefit.' Over the past couple of years, the number of BCI trial volunteers has soared. This year, China became the first country to approve a BCI for medical use.

Advances in technology are allowing engineers to provide more features than ever. BCIs come in different forms. Harrell's device includes a set of electrodes embedded in his brain that pick up the electrical activity associated with speech.

Those electrodes are connected to two docking ports on top of his head that can be plugged into a computer. That computer is loaded with software trained to decode his brain signals into phonemes (units of sound in speech) and predict what Harrell wants to say. He can then use an eye gaze tracker to make any corrections before the speech is played out loud.

But some BCIs don't need to be 'plugged in'—they're fully implanted and wireless. Others are less invasive; they might involve placing wired electrodes on the surface of the brain or simply wearing a cap of electrodes, for example. There are trade-offs—the closer you get to the neurons you want to record from, the better your signal will be.

But generally speaking, the more invasive the surgery, the higher the risk of complications. BCIs can also have different functions. Harrell has ALS, but most BCIs in use today are sitting in the brains of people with spinal cord injuries.

Typically, these individuals have some degree of paralysis; for example, they may be unable to move their arms and legs, but their face and ability to speak are unaffected. In those cases, BCIs can be used to control other kinds of devices that might help with mobility. In 2024, Michelle Patrick-Krueger, then at the University of Houston, and her colleagues published a roundup of all trials of BCIs conducted between 1998, which is when they believe the first device was implanted, and the end of 2023.