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A new neural implant revolutionizes the monitoring of brain activity by combining superficial and deep brain data collection in a minimally invasive way. Scientists from the University of
A new neural implant revolutionizes the monitoring of brain activity by combining superficial and deep brain data collection in a minimally invasive way. Scientists from the University of California, San Diego have developed a neural implant that provides information about activity deep within the brain while sitting on its surface. The implant consists of a thin, transparent and flexible polymer tape filled with a dense array of graphene electrodes. T
A technology being tested in transgenic mice moves researchers closer to creating a minimally invasive brain-computer interface (BCI) that provides high-resolution data on deep neural activity using recordings from the brain surface. The study will be published in the journal today (January 11). Nature Nanotechnology.
“With this technology, we are expanding the spatial scope of neural recordings,” said senior study author Duigu Kuzum, a professor in the Department of Electrical and Computer Engineering at UC San Diego Jacobs School of Engineering. “Although our implant is on the surface of the brain, its design goes beyond physical perception because it can elicit neural activity from deeper layers.”
When placed on the surface of the brain, this thin, flexible implant allows researchers to obtain high-resolution information about neural activity deep within the brain without damaging its delicate tissue. Credits: David Bailot/University of California, San Diego Jacobs School of Engineering
This study overcomes the limitations of modern nerve implantation technologies. For example, current surface arrays are minimally invasive but lack the ability to obtain information beyond the outer layers of the brain. In contrast, fine-needle electrode arrays penetrating the brain can probe deeper layers, but they often cause inflammation and scarring, which degrades signal quality over time. A new nerve implant developed at the University of California, San Diego offers the best of both worlds.
The implant is a thin, transparent and flexible polymer strip that adapts to the brain surface. The strip is embedded in an array of small, round, high-density graphene electrodes, each 20 micrometers in diameter. Each electrode is connected via a graphene wire from a micrometer to a mounting board.
In tests on transgenic mice, the implant allowed the researchers to simultaneously obtain high-resolution information about two types of neuronal activity: electrical activity and calcium activity. When the implant was placed on the surface of the brain, it recorded electrical signals from neurons in the outer layers. At the same time, the researchers used a two-photon microscope to shine laser light through the implant to image calcium spikes in neurons located 250 micrometers below the surface. The researchers found a correlation between electrical signals at the surface and calcium flares in deeper layers. This correlation allowed researchers to use surface electrical signals to train neural networks to predict calcium activity at different depths—not just for large populations of neurons, but also for individual neurons.
Close-up of an array of graphene electrodes. Credits: David Bailot/University of California, San Diego Jacobs School of Engineering
“The neural network model was trained to learn the relationship between electrical recordings on the surface and the calcium ion activity of neurons at depth,” Kuzum said. “Once we learn this connection, we can use the model to predict deep activity from the surface.”
The advantage of being able to predict calcium activity from electrical signals is that it overcomes the limitations of imaging experiments. It is necessary to stabilize the subject’s head under the microscope when visualizing calcium increases. Additionally, these experiments may only last an hour or two.
“Because electrical recordings do not have these limitations, our technology allows for longer experiments in which the subject can move freely and perform complex behavioral tasks,” said electrical and computer engineer Mehrdad Ramezani, one of the study’s authors. PhD student in Kuzuma’s laboratory. “This may provide a more complete understanding of neural activity in dynamic real-world scenarios.”
This technology owes its success to several innovative design features: transparency and high electrode density, as well as machine learning methods.
“This new generation of high-density embedded transparent graphene electrodes allows us to analyze neuronal activity with higher spatial resolution,” Kuzum said. said. “As a result, the quality of the signal improves significantly. What makes this technology even more remarkable is the integration of machine learning techniques that make it possible to predict deep neural activity from surface signals.”
This study was the result of a collaborative effort between several research groups at the University of California, San Diego. The team led by Kuzum, one of the world leaders in the development of multimodal neural interfaces, includes nanoengineering professor Ertuğrul Kubukka, who specializes in advanced micro and nanotechnology for the production of graphene materials; Vikash Gilja, Professor of Electrical and Computer Engineering, whose laboratory combines subject-specific expertise in basic neuroscience, signal processing, and machine learning for decoding neural signals; and Takaki Komiyama, professor of neurobiology and neuroscience, whose laboratory focuses on the study of neural circuit mechanisms underlying flexible behavior.
Transparency is one of the key features of this neural implant. Conventional implants use opaque metallic materials for their electrodes and wires, which prevents visibility of neurons beneath the electrodes during imaging experiments. In contrast, an implant made using graphene is transparent and provides a perfectly clear field of view for the microscope during imaging experiments.
“The simultaneous full integration of electrical signal recording and optical imaging of neural activity is only possible with this technology,” Kuzum said. said. “Being able to run both experiments simultaneously gives us more relevant data because we can see how the imaging experiments are related to the electrical recordings over time.”
To make the implant completely transparent, the researchers used ultra-thin, long graphene wires instead of traditional metal wires to connect the electrodes to the printed circuit board. However, Ramezani explained that producing a single piece of graphene as a thin, long wire is difficult because any defects would render the wire dysfunctional. “There may be a gap in the graphene wire that prevents the electrical signal from passing, so you basically end up with a broken wire.”
Researchers solved this problem using a clever technique. Instead of making the wires as a single layer of graphene, they made them as a double layer with nitric acid doped in the middle. “By placing two layers of graphene on top of each other, there is a good chance that defects in one layer will be masked by the other layer, allowing the creation of fully functional, thin and long graphene wires with improved conductivity,” Ramezani said.
According to the researchers, this work demonstrates the most densely packed transparent electrode array on a surface neural implant to date. Achieving the high density required producing extremely small graphene electrodes. This has become a big problem because reducing the size of graphene electrodes increases their impedance, which impedes the flow of electrical current needed to record neural activity. To overcome this obstacle, the researchers used a microfabrication technique developed by Kuzuma’s laboratory that involves depositing platinum nanoparticles onto graphene electrodes. This approach greatly improved the flow of electrons across the electrodes while keeping them small and transparent.
The team will then focus on testing the technology in various animal models, with the ultimate goal of human translation in the future.
Kuzuma’s research group is also committed to using technology to advance basic neuroscience research. In this spirit, they share the technology with laboratories in the US and Europe; They contribute to research ranging from understanding how vascular activity is linked to electrical activity in the brain to investigating how cells in the brain are so effective at creating spatial memory. . To make the technology more accessible, Kuzuma’s team applied for a grant from the National Institutes of Health (NIH) to fund efforts to increase production and promote its use by researchers around the world.
“This technology can be used for a wide range of basic neuroscience research, and we are eager to contribute to accelerating progress towards a better understanding of the human brain,” said Kuzum.
Source: Port Altele
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