Electronics 100


University of California San Diego


The number of electrodes that fit in the newly developed 3cm grid – today’s clinical equivalents can only manage one.


boundaries between, for instance, a patient’s motor and sensory cortexes. The established practice is to incorporate 5–10mm resection margins to avoid causing off-target damage, but that can prevent surgeons from fully removing tumours – and still leaves room for error. It is not a new problem. Today’s ECoG grids are manufactured much as they were when they were first used – all the way back in the 1950s. Millimetre-scale electrodes are pressed into a layer of biocompatible silicone approximately 1mm thick and then hand soldered to electrical wires. For all the technological developments of the past 70 years, human hands remain roughly as dextrous as they


always have been, so significantly improving the resolution offered by ECoG grids means rethinking the entire manufacturing process. That is exactly what Shadi Dayeh, Ahmed Raslan and their team have done. Their next-generation arrays provide electrocorticography for our flat-screen, high- definition age, in more ways than one.


Combine to build


As a neurosurgeon that specialises in resecting tumours from functional brain regions, Raslan, associate professor of neurological surgery at Oregon Health and Science University, has spent a career pushing up against the limitations of handmade ECoG grids. When he saw Dayeh, professor of electrical and computer engineering at the University of California San Diego, presenting an abstract about high-resolution sensor arrays, he knew he had found the “unicorn” that could finally help him overcome them. Together, the duo has developed the idea to incorporate 1,024 or 2,048 ECoG electrodes in 3x3cm and 6x6cm grids just 7µ thick. “It’s very similar to looking at the sun but using a 100 times more powerful telescope,” says Raslan, referring to the 3cm grid that fits 100 electrodes. Today’s clinical equivalents can only manage one. “You start seeing things that you didn’t know existed.” There are plenty more metaphors where that came from. Raslan is almost as good at giving poetic descriptions of the brain as he is at cutting into it. He explains what he has learned about the border between the parts of the brain responsible for movement and sensation, a boundary usually identified with a specific fold in the brain called the central sulcus, with reference to the difficulty of drawing a line between the land and the sea. Without next- generation ECoGs, the observation, and the improvements it could mean for his practice, may not have been possible. “It was clearly evident to us from this very high resolution that the central sulcus may not always be the functional boundary; the functional boundary is different from one human to another,” says Raslan. “And it’s not always in front, behind or parallel to the central sulcus: it can cross. It doesn’t have a linear dimension. It’s like the shoreline.”


66 Medical Device Developments / www.nsmedicaldevices.com


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