Electrocorticography (ECoG)
Electrocorticography (ECoG) is the recording of brain activity from the cortical surface with electrodes placed epidurally, on the dura, or subdurally, on the pia, rather than through the scalp or into the tissue.
It sits between scalp EEG and penetrating recording: finer in space and wider in bandwidth than EEG, because bone and scalp are not in the path, and less invasive than a probe, because nothing enters the cortex. Its clinical history and analysis methods are standard material; what follows is what changes when the electrode is a thin-film grid.
The grid records the field potential of the population under each site, not spikes, so the signal is chosen by site size and placement. Epidural placement leaves the dura intact and behaves better chronically, but the dura attenuates and blurs what reaches the sites; subdural placement gives higher amplitude and finer resolution, including high-gamma activity, at the cost of opening it. Site diameter sets the area averaged, from 25 µm for micro-ECoG that resolves columns to a millimeter for a regional signal, and site pitch sets how fine a spatial claim the map can make. A 12 µm polyimide grid conforms to the curvature and movement of the cortex, which is what keeps every site in contact; the ECoG series holds the 33 catalog layouts, and the reference decision is worked through in the grid referencing guide.
Typical values
| Placements | epidural (on dura) or subdural (on pia) |
|---|---|
| Signal | field potential; no single-unit spikes |
| Catalog ECoG grid site diameter | 25 µm to 1 mm |
| Catalog ECoG designs | 33; 4 to 256 sites |