A brain or neural implant that provides information about the deep activity of the brain while remaining on its surface has just been developed by researchers at the University of California, San Diego (USA). This implant consists of a thin, transparent and flexible polymer strip and is equipped with a dense network of graphene electrodes.
This technology, tested in transgenic mice, brings researchers one step closer to creating a minimally invasive brain-computer interface (BCI) that uses recordings from the brain surface to provide high-resolution data on deep neuronal activity.
Innovative technology
The new neural implant developed at UC San Diego offers the best of both worlds. The implant is a thin, transparent, flexible polymer strip that conforms to the surface of the brain. The tape is inlaid with a high-density network tiny circular graphene electrodes, each 20 micrometers in diameter. Each electrode is connected to a circuit board via a graphene wire a few micrometers thick.
When the implant is placed on the surface of the brain, it records 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 obtain images of the calcium spikes of neurons up to 250 micrometers below the surface.
Close-up of graphene electrode array. Photo credit: David Baillot/UC San Diego Jacobs School of Engineering
Promising results
The researchers found a connection between surface electrical signals and calcium spikes in deeper layers. This correlation allowed researchers to use surface electrical signals to train neural networks to predict calcium activity—not only for large populations of neurons, but also for individual neurons—at different depths.
An advantage of being able to predict calcium activity from electrical signals is that it overcomes the limitations of imaging experiments. When imaging calcium peaks, the subject's head must be fixed under the microscope. These experiences may only last an hour or two each.
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For better understanding
What is a nerve implant?
A neural implant is a medical device designed to stimulate, record or block signals in the brain. These implants can be used to treat various neurological diseases such as Parkinson's, epilepsy and depression.
What is a Brain-Computer Interface?
A brain-computer interface (BCI) is a system that allows direct communication between the brain and an external device. BCIs are used in biomedical research and neuroprosthetics, but also have potential applications in defense.
What is Graphene?
Graphene is an allotropic form of carbon consisting of a single plane of carbon atoms arranged in a hexagonal lattice. It is extremely strong, lightweight, transparent and conductive, making it suitable for a wide range of applications, from electronics to medicine.
What is calcium activity in the brain?
Calcium activity in the brain refers to fluctuations in calcium concentration in neurons, which play a key role in how neurons communicate with each other. Calcium activity can be measured using special imaging techniques.
What advantages does this new technology offer?
This new technology provides high-resolution information about deep neuronal activity that could improve our understanding of the brain and help develop new treatments for neurological disorders.
References
Image: This thin, flexible implant is placed on the surface of the brain and allows researchers to collect high-resolution information about neuronal activity in the brain without damaging its delicate tissue. Photo credit: David Baillot/UC San Diego Jacobs School of Engineering
Article “High-density transparent graphene arrays for predicting cellular calcium activity at depth from surface potential recordings” – DOI: 10.1038/s41565-023-01576-z
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