Flexible brain implants, with minimal intrusion, could well become a reality in mapping brain activity. A new research has led to the development of a device that could treat neurological and psychiatric ailments by identifying origins of seizures in the brain for further medical intervention. In fact, the study believes that the new implantable array made up of silicon nanomembrane transistors is the first of its kind to be used as a brain interface.

Lead researcher, Jonathan Viventi, at the Polytechnic Institute of New York University, and his team of researchers have devised a streamlined, minimally invasive brain interface that could bring across a new understanding of brain diseases like epilepsy, as well as usher in a new generation of implantable neuroprosthetic and diagnostic devices.

The research could perhaps lead to medical applications such as improvements of existing implantable devices such as cardiac pacemakers and defibrillators, cochlear and retinal implants and motor prosthetic systems.

In the long run, the research aims to configure implantable arrays for use anywhere in the body, equipped with minimum wire-controlled sensors capable of multiple functions such as recording, stimulating or ablating unwanted seizure areas.

The newly designed array is likely to overcome shortcomings of the 20 odd drugs available for treating epilepsy that do not always have the capability of controlling seizures accurately enough, causing recurrences in convulsion episodes.

In cases where surgery is the only option for controlling seizures, electrode arrays have been used to map brain activity. But the arrays currently available lack flexibility in adjusting to the folds of the brain. This leads to minimal coverage and therefore fails to control seizures to the utmost capacity.

An advantage of the new design developed by Viventi and team is that the device is ultra-thin and capable of recording brain activity from the cortical surface without having to use penetrating electrodes.

Another advantage seen is to replace currently used devices that can be clumsy and of low resolution, or do away with devices that are used for neuromotor prostheses leading to tissue inflammation and hemorrhages.

The study, published in Nature Neuroscience, explains the benefits of using an electrode array made of a pliable material with thickness about a quarter of a human hair in mapping brain activity. The electrode array adjusts itself to the brain's surface, enabling a better understanding of epileptic seizures.

The newly designed device is composed of 720 silicon nanomembrane transistors in a multiplexed 360-channel array. This 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 available arrays require separate wires for each individual sensor, for measuring broad regions of the brain with low resolution or small regions with high resolution, but not both. The multiplexed nanosensor of the new device has shown to cover a much larger brain area with high resolution, while using almost ten times fewer wires.

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, lead author and Associate Professor of Neurology at the Perelman School of Medicine and Bioengineering at the University of Pennsylvania. The study was in collaboration with John Rogers, University of Illinois Urbana-Champaign, and Dae-Hyeong Kim from Seoul National University.

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, it could allow us to intervene to make patients better, Litt said.

The circuits we're familiar with are built on rigid silicon, which doesn't conform to the body. Ultrathin silicon retains its performance while being flexible, and is much better suited to implantable devices. It's the difference between a piece of paper and a piece of 2x4 lumber - same material, dramatically different properties, Viventi explained. The researchers believe this is the first reported use of ultrathin, flexible silicon in a brain interface device.

In animal models, researchers observed responses to visual stimuli and recorded previously unknown details of sleep patterns and brain activity during epileptic seizures.

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 characterizing and treating chronic pain, depression, and other neuropsychological disorders.

The researchers hope to, one day, roll the array into a tube and send it into the brain through a small hole instead of opening up the skull.

In the final analysis, the researchers aim to develop flexible electrode arrays that could be perfected for use in various therapeutic and research functions.

The largescale impact could be utilized to incorporate the array for neuroprostheses, pacemakers, ablative devices, or neuromuscular stimulators. The researchers believe that the versatility, sensitivity and reduced effect on surrounding tissues could make the new ultrathin brain interface a forerunner for next generation brain-computer interfaces.

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