Miryam Naddaf in Nature: Moving a prosthetic arm. Controlling a speaking avatar. Typing at speed. These are all things that people with paralysis have learnt to do using brain–computer interfaces (BCIs) — implanted devices that are powered by thought alone. These devices capture neural activity using dozens to hundreds of electrodes embedded in the brain. A decoder system analyses the signals and translates them into commands. Although the main impetus behind the work is to help restore functions to people with paralysis, the technology also gives researchers a unique way to explore how the human brain is organized, and with greater resolution than most other methods.
Scientists have used these opportunities to learn some basic lessons about the brain. Results are overturning assumptions about brain anatomy, for example, revealing that regions often have much fuzzier boundaries and job descriptions than was thought. Such studies are also helping researchers to work out how BCIs themselves affect the brain and, crucially, how to improve the devices. “BCIs in humans have given us a chance to record single-neuron activity for a lot of brain areas that nobody’s ever really been able to do in this way,” says Frank Willett, a neuroscientist at Stanford University in California who is working on a BCI for speech. The devices also allow measurements over much longer time spans than classical tools do, says Edward Chang, a neurosurgeon at the University of California, San Francisco. “BCIs are really pushing the limits, being able to record over not just days, weeks, but months, years at a time,” he says. “So you can study things like learning, you can study things like plasticity, you can learn tasks that require much, much more time to understand.”
Recorded history
The idea that the electrical activity of the human brain could be recorded first gained support 100 years ago. German psychiatrist Hans Berger attached electrodes to the scalp of a 17-year-old boy whose surgery for a brain tumour had left a hole in his skull. When Berger recorded above this opening, he made the first observation of brain oscillations and gave the measurement a name: the EEG (electroencephalogram).
Researchers immediately saw that recording from inside the brain could be even more valuable; Berger and others used surgery to place electrodes on the surface of the cortex to study the brain and diagnose epilepsy. Recording from implanted electrodes is still a standard method for pinpointing where epileptic seizures begin, so that the condition can be treated using surgery.
Then, in the 1970s, researchers began to use signals recorded from further inside animal brains to control external machines, giving rise to the first implanted brain–machine interfaces.
In 2004, Matt Nagle, who was paralyzed after a spinal injury, became the first person to receive a long-term invasive BCI system that used multiple electrodes to record activity from individual neurons in his primary motor cortex1. Nagle was able to use his system to open and close a prosthetic hand, and to perform basic tasks with a robotic arm.
Researchers have also used EEG readings — collected using non-invasive electrodes placed on a person’s scalp — to provide signals for BCIs. These have allowed paralysed people to control wheelchairs, robotic arms and gaming devices, but the signals are weaker and the data less reliable than with invasive devices.
So far, about 50 people have had a BCI implanted, and advances in artificial intelligence, decoding tools and hardware have propelled the field forwards.
Electrode arrays, for instance, are becoming more sophisticated. A technology called Neuropixels has not yet been incorporated into a BCI, but is in use for fundamental research. The array of silicon electrodes, each thinner than a human hair, has nearly 1,000 sensors and is capable of detecting electrical signals from a single neuron. Researchers began using Neuropixels arrays in animals seven years ago, and two papers published in the past three months demonstrate their use for questions that can be answered only in humans: how the brain produces and perceives vowel sounds in speech2,3.
Commercial activity is also ramping up. In January, the California-based neurotechnology company Neuralink, founded by entrepreneur Elon Musk, implanted a BCI into a person for the first time. As with other BCIs, the implant can record from individual neurons, but unlike other devices, it has a wireless connection to a computer.
And although the main driver is clinical benefit, these windows into the brain have revealed some surprising lessons about its function along the way. More here.
