Flexible neural sheet device reaches deep cortical regions without brain penetration

Implanting a device into the deep temporal cortex of a mouse without damaging the brain has long been a major challenge in neuroscience research. A team at Meijo University and Dokkyo Medical University has now overcome this barrier with a flexible sheet thinner than a human hair that slides into place without penetrating the brain.

The device, described in Applied Physics Express, puts 16 micro-LEDs and 32 recording electrodes onto a parylene C sheet just 25 µm thick. Instead of being inserted into the brain, the device slips into the epidural space — the narrow gap between the skull and the brain surface — allowing broad cortical coverage from the parietal region to the deep temporal area with a single placement.

This wide coverage is a key advantage. Regions such as the insular and piriform cortex are　located in the temporal and deep area, and are indispensable for processing multimodal sensory inputs. In mice, these regions lie beneath the temporalis muscle and skull, making them difficult to access using conventional surface devices. While needle probes can reach these areas, they cause tissue damage and cover only a limited region.

The major technical challenge in making the sheet sufficiently thin was the LEDs. Standard LED chips are typically over 50 µm thick, making them unsuitable for this applications. To overcome this limitation, the team developed a process to bond InGaN-based LED thin films onto the parylene C substrate using indium metal at 160°C — below the temperature at which the polymer begins to degrade.

In experiments using mice genetically engineered to express a light-sensitive protein in cortical neurons, the device successfully recorded evoked responses from four sensory areas — visual, auditory, somatosensory, and olfactory — in a single mouse with a single device placement. Moreover, selective micro-LED stimulation reliably evoked neural responses at specific cortical sites. No such responses were observed in wild-type mice, confirming that the recorded signals reflected genuine neural activity.

“Our previous work showed that a flexible film could reach the temporal cortex. Here, we successfully integrated micro-LEDs into that film without degrading their performance. For the first time, we can both record and stimulate neural activity across a wide cortical area using a single device,” said Professor Hiroto Sekiguchi of Meijo University.

“We have previously recorded from multiple cortical areas, but there has been no way to simultaneously stimulate and record wide cortical activity with a single device. This bidirectional capability — enabling both intervention and observation — allows experiments to investigate causal relation of cortical activity impossible before,” said Professor Noriaki Ohkawa of Dokkyo Medical University, who led the animal experiments.

This research was supported by the Japan Science and Technology Agency (JST), the Japan Agency for Medical Research and Development (AMED), and the Canon Foundation.

About Meijo University

Meijo University traces its origin back to the establishment of the Nagoya Science and Technology Course in 1926, giving it a proud history of more than 90 years. As one of the largest universities in the Chubu region, Meijo University is a comprehensive learning institution that supports a wide range of academic fields from the humanities to physical sciences. With a network of more than 200,000 graduates and alumni, it strives to contribute not only to local industries but also to international communities in various fields. Meijo University is also known as the birthplace of the carbon nanotube. To foster the human resources of the next generation, the university continues to tackle ongoing challenges by further enhancing its campus and creating new faculties.

Website: https://www.meijo-u.ac.jp/english/