Transparent neural implant provides window to deeper brain activity

The graphene wires inside the film measure only 20 micrometers in diameter
David Baillot/UC San Diego Jacobs School of Engineering
The graphene wires inside the film measure only 20 micrometers in diameter
David Baillot/UC San Diego Jacobs School of Engineering

Researchers have created a thin transparent neural implant that can monitor activity on the brain's surface but also account for functions at a deeper level. The hope is that it will lead to an accurate but less invasive brain-computer interface.

While implants that allow computers to read the activity taking place in the brain are advancing at a steady pace, a fundamental conundrum in the field exists. Implants that read activity deep inside our gray matter consist of probes that can cause issues including inflammation and scarring, and the signals they provide can degrade over time. Implants that sit on the surface of the brain do not have such issues, but they can't give scientists a read on anything more than the signals skittering across the brain's surface.

Now, researchers at the University of California San Diego (UCSD) have taken a step that tackles this issue. They created a super-thin polymer film consisting of two layers of transparent graphene wires sandwiched around a layer of nitric acid. After placing the transparent film on the brains of transgenic mice, the team was able to read surface signals from the rodents' brains. The real advance, though, comes about because the film is transparent. This allowed the researchers to simultaneously shoot lasers through it and use a two-photon microscope to image calcium spikes from neurons that were up to 0.25 mm below the surface. Calcium is a key component of the way in which neurons transmit data to each other.

The researchers were then able to train a machine learning model to establish the link between surface activity and sub-surface activity, in effect teaching it to understand what is happening deeper in the brain based on what the sensor picks up from surface signals.

“We are expanding the spatial reach of neural recordings with this technology,” said study senior author Duygu Kuzum. “Even though our implant resides on the brain’s surface, its design goes beyond the limits of physical sensing in that it can infer neural activity from deeper layers.”

The researchers also point out that currently, in order to observe calcium activity inside the brain, scientists need to fix a subject's head beneath a microscope in procedures that can last up to two hours at most. The new UCSD implant does not have this limitation.

“Since electrical recordings do not have these limitations, our technology makes it possible to conduct longer duration experiments in which the subject is free to move around and perform complex behavioral tasks,” said study co-first author Mehrdad Ramezani. “This can provide a more comprehensive understanding of neural activity in dynamic, real-world scenarios.”

Next, the researchers will test their implant on other animal models with an eye towards eventual human trials. They've also shared their findings with other labs across the US and Europe with the hope of speeding up the technology's development.

“This technology can be used for so many different fundamental neuroscience investigations, and we are eager to do our part to accelerate progress in better understanding the human brain,” said Kuzum.

The research has been published in the journal Nature Technology.

Source: UC San Diego via EurekAlert

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