A new, ultrathin, ultraflexible implant loaded with sensors can record the electrical storm that erupts in the brain during a seizure with nearly 50-fold greater resolution than was previously possible. The level of detail could revolutionize epilepsy treatment by allowing for less invasive procedures to detect and treat seizures. It could also lead to a deeper understanding of brain function and result in brain-computer interfaces with unprecedented capacity.
Current technology has stalled out at a sensor array with about eight sensors per square centimeter; the new array—built in collaboration with John Rogers, a professor of materials science and engineering at the University of Illinois Urbana-Champaign—can fit 360 sensors in the same amount of space. To create a small device so densely packed with sensors, Rogers integrated electronics and silicon transistors into the array itself, drastically reducing the amount of wiring
Brain map: An ultrathin array of electrodes, shown at top being inserted into the brain of a cat, allows for data acquisition far greater than ever before possible. At bottom, the electrode array is so flexible that it can fold around even the slimmest objects, allowing for easy insertion and good coverage of uneven surfaces.
In their first test of the device, on a cat with epilepsy, Litt, Rogers, and graduate student Jonathan Viventi (now an assistant professor studying translational neuroengineering at New York University), saw something striking: a storm of activity that looked like a self-propagating spiral wave. The pattern, only apparent with incredibly high-resolution recording, is remarkably similar to one seen in cardiac muscle during a life-threatening condition called ventricular fibrillation.
Rather than large sections of the brain being responsible for seizures, something Litt says has traditionally been thought to occur, it appears to instead stem from multiple clusters of very small areas, or “microdomains,” in the cortex.
The device could also enable less-invasive testing and treatment. Rather than cutting open a large section of skull to place a monitoring device, Litt says, the new implant could allow surgeons to drill just a small hole through which to slip the slim, rolled-up sensor array, and unfurl it onto the brain’s surface once it’s inside. And instead of removing areas of brain the size of a golf ball, it might be possible to just remove the microdomains and leave the rest of the cortex intact.
The current version of the device is one square centimeter; for human use, researchers need to expand it to about eight square centimeters. A startup called MC10 will work on making it larger and production-ready.
Litt and Rogers are now working to create an implant with stimulators embedded next to the sensors. If they can build a device that not only detects the onset of a seizure but can just as quickly provide electrical stimulation to quash it, the research could have great clinical impact. “This isn’t just a research tool. It has a clearly defined mode of use in the clinical setting,” Rogers says. “This is a piece of biointegrated electronics that is unmatched in its functionality, and the proof is in the pudding.”
Arrays of electrodes for recording and stimulating the brain are used throughout clinical medicine and basic neuroscience research, yet are unable to sample large areas of the brain while maintaining high spatial resolution because of the need to individually wire each passive sensor at the electrode-tissue interface. To overcome this constraint, we developed new devices that integrate ultrathin and flexible silicon nanomembrane transistors into the electrode array, enabling new dense arrays of thousands of amplified and multiplexed sensors that are connected using fewer wires. We used this system to record spatial properties of cat brain activity in vivo, including sleep spindles, single-trial visual evoked responses and electrographic seizures. We found that seizures may manifest as recurrent spiral waves that propagate in the neocortex. The developments reported here herald a new generation of diagnostic and therapeutic brain-machine interface devices.