SuperEEG: ECoG data breaks free from electrodes

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SuperEEG: ECoG data breaks free from electrodes


The "gold standard" for measuring neural activity in human brains is ECoG (electrocorticography), using electrodes implanted directly onto the surface of the brain. Unlike methods that measure blood oxygenation (which have poor temporal resolution) or that measure signals on the scalp (which have poor spatial resolution), ECoG data has both high spatial and temporal precision. Most of the ECoG data that has been collected comes from patients who are being treated for epileptic seizures and have had electrodes implanted in order to determine where the seizures are starting.

The big problem with ECoG data, however, is that each patient typically only has about 150 implanted electrodes, meaning that we can only measure brain activity in 150 spots (compared to about 100,000 spots for functional MRI). It would seem like there is no way around this - if you don’t measure activity from some part of the brain, then you can’t know anything about what is happening there, right?

Actually, you can, or at least you can guess! Lucy Owen, Andrew Heusser, and Jeremy Manning have developed a new analysis tool called SuperEEG, based on the idea that measuring from one region of the brain can actually tell you a lot about another unmeasured region, if the two regions are highly correlated (or anti-correlated). By using many ECoG subjects to learn the correlation structure of the brain, we can extrapolate from measurements in a small set of electrodes to estimate neural activity across the whole brain.


Figure from their SfN poster

This breaks ECoG data free from little islands of electrodes and allows us to carry out analyses across the brain. Not all brain regions can be well-estimated using this method (due to the typical placement locations of the electrodes and the correlation structure of brain activity), but it works surprisingly well for most of the cortex:


Figure from their SfN poster

This could also help with the original medical purpose of implanting these electrodes, by allowing doctors to track seizure activity in 3D as it spreads through the brain. It could even be used to help surgeons choose the locations where electrodes should be placed in new patients, to make sure that seizures can be tracked as broadly and accurately as possible.