Meanwhile, electrodes placed directly on the scalp can pick up brain waves – electroencephalograms, or EEGs – but they lack the spatial extension of implanted electrodes. Neuroscientists know, very roughly, what part of the brain does what, but the more you know which neurons are firing, the better you can tell what they are firing about.
Another recent innovation, electrocorticography, places a mesh of electrodes directly on the surface of the brain. In combination with smart spectral processing of the signals of those electrodes, ECOG is sufficient to translate action into the part of the motor cortex that controls lips, jaws, and tongues in text or speech. And there are other approaches. CTRL-labs, which Facebook bought for perhaps $ 1 billion in 2019, tries to get motor signals from neurons in the wrist. The kernel uses functional near-infrared spectroscopy on the head to understand brain activity.
The stentode of Oxley and colleagues, if it showed good results, would fit somewhere along the spectrum between the implanted electrode and the EEG. Closer to the first thing than the second, its inventors hope. But it’s early days. “The original technology and original idea is super cool, but given where they’re accessing the signals, I hope it’s a relatively low-fidelity signal relative to other brain-machine interface strategies,” says Vikash Gilja , Which runs the Translational Neural Engineering Lab at UC San Diego. “We at least know that high-density ECOG recordings from the surface of the brain can give information beyond what is shown in this paper.”
One potential problem: the tissue conducts electrical impulses, but the electrodes in the stent are picking up signals from the brain through blood vessel cells. This signal reduces the content. Gilja says, ‘If we would have taken those cortical surface recordings and compared them to the Utah Array Experiments — the bulk of the clinical experience with implanted electrodes. (Just for transparency, I should state that Gilja has paid to work with BCI companies, including Neuralink, with whom Synchron could theoretically compete someday.)
So it may not be good enough for neurology, but it can be very useful for a person with paralysis who wants a low-maintenance BCI that does not require drilling through the skull. “There is a trade-off between how aggressive you want to be and the level at which you want to gather information,” says neuroscientist Andrew Pruszinski of Western University, Canada. “It is trying to reach the middle ground, so that a catheter can be inserted close to the neural activity.” It is clearly invasive, but certainly not as invasive as inserting electrodes into the brain. “