The researchers have already developed a preliminary prototype that is much smaller than the ECoG device used in epilepsy patients. While seizure monitoring requires electrodes to cover a large part of the brain’s surface, a neural interface can run on signals recorded from just a small brain area in the brain. While current ECoG surgeries require the removal of a large chunk of skull, a more compact technology could be delivered through a small burr hole in the skull.
Moran is testing the smaller device, which is about the size of three or four stacked quarters, in monkeys to determine its long-term potential, as well as the optimal parameters for an ECoG-based neural interface. For example, the researchers need to determine the number of electrodes that can be packed into the smallest space and still record enough independent information from the brain to control a prosthetic arm with multiple degrees of freedom. (The shoulder has three degrees of freedom, and the elbow two, all of which must be controlled by independent signals in the brain.)
One of the biggest issues in developing neural prostheses is creating a device that can record signals from the brain reliably over time. Electrodes implanted into the brain typically function well for only six to twelve months because the immune system attacks the electrode, encapsulating it in tissue and degrading the quality of the recorded signal. (There have been instances of implanted electrodes lasting for years, however.)
“What we really want is for these devices to work for a decade, but at least three to five years,” says Moran. So far, the small ECoG devices have been implanted in monkeys for about eight months, so it’s not yet possible to compare long-term durability and safety to that of more deeply implanted electrodes. Moran believes that because the device does not penetrate brain tissue, it will be less susceptible to immune attack.
“At the end of the day, the question is whether they can retain a high quality of recordings for a long period of time,” says Joseph Pancrazio, a program director at the National Institute for Neurological Disorders and Stroke, a government funding agency, in Bethesda, MD, who was not involved in the research. “The jury is still out.” Pancrazio also questions whether the procedure is truly less invasive than that used to implant electrodes into the brain, a technique that is employed clinically for deep brain stimulation, a treatment for Parkinson’s disease.
Neurolutions’ next step will be to build a prototype for clinical testing. Lunney estimates that the company will have a working prototype within the next year to 15 months. In the envisioned prototype, the implanted electrodes would wirelessly send signals to an external device, perhaps in the form of a hat or headband, which would both power the internal component and interpret the incoming information. “We’ve done the wireless communications,” says Lunney. “The challenge is turning it into one little electronics package that can fit into a nineteen-by-seven-millimeter package.”