- KIST develops ultra-thin transparent neural electrode capable of recording neural signals

- Artificial visual signals generated in blind mice match normal brain activity at 78 percent

A large-area, ultra-thin transparent neural electrode. [Provided by KIST]
A large-area, ultra-thin transparent neural electrode. [Provided by KIST]

South Korean researchers have opened a new path toward restoring vision in patients with retinitis pigmentosa, a degenerative eye disease affecting about 2 million people worldwide.

A joint research team led by Sung Hye-jung and Lim Mae-soon of the Brain Science Institute at the Korea Institute of Science and Technology (KIST) has developed an ultra-thin transparent neural electrode that can both deliver light to the brain and cleanly record the neural signals produced by that light stimulation.

Restoring artificial vision requires optogenetics — a technology that uses light to activate neurons. At the same time, accurately measuring the brain's neural signals is essential to verify the quality of the artificial vision and improve the efficiency of light stimulation. Conventional metal electrodes, however, either block the light needed for optogenetics or, when light does pass through, generate strong electrical noise that drowns out brain signals. The field has long faced a fundamental dilemma: materials transparent enough to pass light tend to conduct electricity poorly, while good electrical conductors tend to block light.

The research team solved this by developing a transparent electrode just one-fifteenth the thickness of a human hair. Conducting electricity through an electrode requires metal, but as a metal layer grows thinner, its atoms tend to cluster together and block light. The team applied a special coating to the electrode surface before depositing the metal, causing gold atoms to spread out thinly and evenly — much like oil spreading across water. As a result, the gold film thickness was reduced from the conventional 100 nanometers to just 10 nanometers. The electrode's total thickness is only about 4 micrometers, allowing it to conform naturally to the brain's surface.

The electrode transmits more than 65 percent of incoming light while maintaining electrical signal-recording performance comparable to existing electrodes. Electrical noise during light stimulation was reduced by up to 74 percent, and the electrode retained its performance even after being bent and straightened 20,000 times.

When the team placed the electrode on the brain surface of blind mice and stimulated neurons using blue-light-based optogenetics, it generated artificial visual neural signals matching those of normally sighted mice at a 78 percent rate — a world first. The result demonstrates that stimulating the brain's visual cortex with light can induce responses closely resembling actual sight.

The cover of Advanced Functional Materials, an international journal in materials science. [Provided by KIST]
The cover of Advanced Functional Materials, an international journal in materials science. [Provided by KIST]

The research points to the possibility of achieving high-quality artificial vision. Applying the same principle to the brain regions responsible for hearing and touch could extend the technology to treatments for hearing loss and tactile restoration. The electrode is also expected to serve as a key component in brain-computer interface (BCI) systems that read brain signals and autonomously adjust stimulation.

"The ability to simultaneously handle light delivery and signal recording lays the groundwork for advanced BCI systems, and we expect it will bring us one step closer to improving the quality of life for people suffering from intractable neurological and sensory disorders," said Lim Mae-soon, a principal researcher at KIST.

Senior researcher Sung Hye-jung said the same principle could be applied to assist people with hearing loss by stimulating the auditory region of the brain, and could also be used for tactile restoration. "It can also be applied to flexible displays, skin-attachable health sensors and organic solar cells," she added.

The findings were published as the cover paper of the latest issue of Advanced Functional Materials, an international journal in materials science.


nbgkoo@heraldcorp.com