For brain and spinal cord injuries, these systems can eventually restore communication and movement, allowing them to live more independently. But at present, they are not all that real. Most require clunky set-ups and cannot be used outside of a research lab. Individuals equipped with a brain implant are also limited in the type of action they can perform because a relatively small number of neurons can record a single implant at once. The most common brain chip, the Utah Array, is a bed of 100 silicon needles, each with an electrode at the tip that is stuck to the brain tissue. One of these arrays is the size of Abraham Lincoln’s face in US dollars and it can record the activity of hundreds of nearby neurons.
But there are many functions of the brain that researchers are interested in – such as memory, language and decision-making involving networks of neur neurons that are widely distributed in the brain. “To understand how these functions actually work, you need to study them at the system level,” said Chantelle Pratt, an associate professor of psychology at the University of Washington who is not involved in the Neurogren project. His work involves a non-invasive brain-computer interface that is worn on the head instead of implants.
The ability to record from many more neurons can enable much better motor control and extend what is currently possible through brain-controlled devices. Researchers can also use them in animals to learn how different parts of the brain communicate with each other. “When it comes to how the brain works, whole parts are more important than the sum of parts,” he says.
Distributed neural implant systems may not be needed for many near-term uses, such as enabling basic motor functions or computer use, says Florian Solzbacher, co-founder and manufacturer of BlackRock Neurotech, Utah Array. However, more complex applications will require more complex set-ups, such as memory or consciousness recovery. “Clearly, the Holy Grail is a technology that can record from as many neurons as possible across the entire brain, surface and depth,” he says. “Do you need the full complexity of it now? Probably not. But in terms of understanding the brain and seeing future applications, the more information we have, the better.”
Smaller sensors can also cause less damage to the brain, he continued. The current array, although already small, can cause inflammation and scarring around the implant site. Brown is not involved in the research, Soljbachter said, “Generally, the smaller the thing you make, the less likely it is to be identified as a foreign object by resistance.” When the body detects a foreign object like a splinter, it tries to dissolve and destroy it, or cover it with scar tissue.
But while the smaller may be better, it’s not necessarily stupid, Soljbachar warns. Even miniscule implants can trigger immunity, so neurogranes also need to produce biocompatible materials. A major hurdle in making a brain implant is to try to minimize damage during the construction of a long-term implant, to avoid the risk of replacement surgery. Current arrays last about six years, but many stop working very quickly because of scar tissue.
If neurogranes are the answer, there are still questions about how they are found in the brain. In their rat experiment, Brown researchers removed a large portion of the rat’s skull, which for obvious reasons would not be ideal for humans. Current implanted arrays require drilling a hole in the patient’s head, but Brown’s team wants to avoid invasive brain surgery altogether. To do this, they are using a special device to develop a neurogreen ert with a thin needle threaded into the skull. (Neuralink is following a robot like a “sewing machine” to deliver its coin-shaped brain implants.)