In order to better understand brain circuitry, recording brain cortical activity with high spatial and temporal resolution is critical. This is especially useful when trying to understand physiological and pathological conditions. Now, a new array of brain sensors has been developed that can record electrical signals directly from the surface of the human brain in record-breaking detail.

A new array of brain sensors can record electrical signals directly from the surface of the human brain in record-breaking detail. [David Baillot / UC San Diego Jacobs School of Engineering]
The team developed reconfigurable thin-film, multithousand-channel neurophysiological recording grids using platinum nanorods (PtNRGrids). The new brain sensors feature densely packed grids of either 1,024 or 2,048 embedded electrocorticography (ECoG) sensors. For comparison, the ECoG grids most commonly used in surgeries today typically have between 16 and 64 sensors, although research-grade grids with 256 sensors can be custom made.

If approved for clinical use, the technology would offer surgeons brain-signal information directly from the surface of the brain’s cortex in 100 times higher resolution than what is available today. Access to this highly detailed perspective on which specific areas of the tissue at the brain’s surface, or cerebral cortex, are active, and when, could provide better guidance for planning surgeries to remove brain tumors and surgically treat drug-resistant epilepsy.

The work is published in the journal Science Translational Medicine in the paper titled, “Human brain mapping with multithousand-channel PtNRGrids resolves spatiotemporal dynamics.

Recording brain activity from grids of sensors placed directly on the surface of the brain—electrocorticography (ECoG)—is already in common use as a tool by surgeons performing procedures to remove brain tumors and treat epilepsy in people who do not respond to drugs or other treatments. Being able to record brain signals at such high resolution could improve surgeons’ ability to remove as much of a brain tumor as possible while minimizing damage to healthy brain tissue. In the case of epilepsy, higher resolution brain-signal recording capacity could improve a surgeon’s ability to precisely identify the regions of the brain where the epileptic seizures are originating, so that these regions can be removed without touching nearby brain regions not involved in seizure initiation.

Demonstrating that ECoG grids with sensors in the thousands function well also opens new opportunities in neuroscience for uncovering a deeper understanding of how the human brain functions.

Recording brain signals at higher resolution is attributable to the team’s ability to place individual sensors significantly closer to each other without creating problematic interference between nearby sensors.

The new brain sensors feature thin, flexible and densely packed grids of either 1,024 or 2,048 embedded electrocorticography (ECoG) sensors. [David Baillot / UC San Diego Jacobs School of Engineering]
While using platinum-based sensors for recording electrical activity from neurons in the brain is not new, the research team is using platinum in a novel way: nanoscale platinum rods. The nano-rod shape offers more sensing surface area than flat platinum sensors, which helps to make the sensors more sensitive.

The platinum nano-rod-based sensor grids are thinner and more flexible than today’s clinically approved ECoG grids. The thinness and flexibility allows the sensor grids to move with the brain, enabling a closer connection and better readings. In addition, the grids are manufactured with small, ring-shaped holes that allow cerebral spinal fluid to pass through. In this way, these perfusion holes support a better interface between the sensor grid and the brain surface by allowing the sensor to easily and safely displace the fluid.

The new platinum nano-rod brain sensor grids are ten micrometers thick, 100 times thinner than the one-millimeter thick and clinically approved ECoG grids. The nano-rods are embedded in a transparent, soft, and flexible biocompatible material called parylene which is in direct contact with the surface of the brain. The electrical signals travel from the brain, through the cerebrospinal fluid, and reach the exposed surfaces of the platinum nano-rods which are recessed within the parylene. This design yields a sensor grid that forms a close and stable connection with the surface of the brain, improving signal quality.

The team has implemented design improvements geared specifically for clinical use. For example, customized sensor grids can be printed with specialized holes that allow surgeons to insert probes at exactly the right spot and apply electrical stimulation directly to brain tissue at specific locations. With the goal of getting higher-resolution ECoG grids approved for clinical use, the researchers have co-founded a startup called Precision Neurotek.

Some of the team’s newly published data from studies in rats also demonstrate the utility of the grids for opening new avenues in fundamental neuroscience research. The paper includes what the researchers believe is the first mapping of a cortical column in a rat from brain-surface recordings. In the past, the mapping of cortical columns has only been done by placement of an individual needle at the surface of the brain and sequential electrical stimulation and movement of the needle across the brain surface. More generally, the fact that the platinum nano-rod grids provide high resolution data in both time and space opens up many new possibilities for uncovering new knowledge about how the brain works.

Longer-term plans include working on wireless versions of these high-resolution ECoG grids that could be used for up to 30 days of brain monitoring for people with intractable epilepsy. The technology also holds potential for permanent implantation to improve the quality of life of people who live with paralysis or other neurodegenerative diseases that can be treated with electrical stimulation such as Parkinson’s disease, essential tremor, and the neurological movement disorder called dystonia.

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