More flexible window into the brain

The work was published in Nature Neuroscience.

"The new technology we have created can conform to the brain's unique geometry, and records and maps activity at resolutions that have not been possible before," says Brian Litt, MD, the study's senior author and Associate Professor of Neurology at the Perelman School of Medicine and Bioengineering at the University of Pennsylvania. "Using this device, we can explore the brain networks underlying normal function and disease with much more precision, and its likely to change our understanding of memory, vision, hearing and many other normal functions and diseases." For our patients, implantable brain devices could be inserted in less invasive operations and, by mapping circuits involved in epilepsy, paralysis, depression and other 'network brain disorders' in sufficient detail, this could allow us to intervene to make patients better, Litt said.

Composed of 720 silicon nanomembrane transistors in a multiplexed 360-channel array, the newly designed ultrathin, flexible, foldable device can be positioned not only on the brain surface but also inside sulci and fissures or even between the cortical hemispheres, areas that are physically inaccessible to conventional rigid electrode arrays. Current arrays also require separate wires for each individual sensor, meaning that they can sample broad regions of the brain with low resolution or small regions with high resolution, but not both. The multiplexed nanosensors of the new device can cover a much large brain area with high resolution, while using almost ten times fewer wires.

Monitoring and studying the brain's constant electrical activity, or to alter it when it goes awry, often requires the placement of electrodes deep within specific regions of the brain. These currently used devices can be clumsy and of low resolution, and those used for neuromotor prostheses can cause tissue inflammation and hemorrhages.

Study collaborators including lead author Jonathan Viventi, PhD, an assistant professor at the Polytechnic Institute of New York University who worked with Litt on the project as a postdoctoral fellow at Penn, and colleagues John Rogers from the University of Illinois Urbana-Champaign, and Dae-Hyeong Kim from Seoul National University, worked together to conceive and build the array, believed to be the first device of its kind to be used as a brain interface.

In animal models, researchers observed responses to visual stimuli and recorded previously unknown details of sleep patterns and brain activity during epileptic seizures. The array recorded spiral waves during seizure activity that have not been previously recorded in whole brain. These patterns are similar to those seen in the heart during ventricular fibrillation, raising the possibility of fighting epilepsy with some of the same methods used to treat cardiac arrhythmias, like focal destruction or ablation of abnormal circuits.

The observation of spiral wave activity also served to highlight the extreme sensitivity and resolving capacity of this new active array, which was able to easily distinguish normal signal patterns from abnormal waves even in the same frequency ranges. The activity recorded by Litt's research team has enormous implications not only for controlling seizures but for understanding and treating disorders of other brain processes affecting sleep, memory, and learning, and for the characterizing and treating chronic pain, depression, and other neuropsychological disorders.

Ultimately, the researchers expect that flexible electrode arrays can be perfected for use for various therapeutic and research purposes throughout the body. They could serve as neuroprostheses, pacemakers, ablative devices, or neuromuscular stimulators. Their versatility, sensitivity, and reduced effect on surrounding tissues puts them in the forefront of the next generation of brain-computer interfaces.

In addition to the National Institutes of Health's National Institute of Neurological Disorders and Stroke (NINDS), the research was supported by the National Science Foundation, the Division of Materials Sciences at the U.S. Department of Energy, Citizens United for Research in Epilepsy, the Dr. Michel and Mrs. Anna Mirowski Discovery Fund for Epilepsy Research, and NIH's National Heart, Lung, and Blood Institute.