What is Electrocorticography?

Recording of electrical brain activity using electrode arrays placed directly on the cortical surface (subdurally or epidurally), providing higher signal quality than scalp EEG without penetrating brain tissue.

What category does Electrocorticography belong to in BCI?

Electrocorticography is a Recording Modalities concept in brain-computer interface science.

Electrocorticography — BCI Glossary

Electrocorticography (ECoG), also known as intracranial EEG (iEEG), involves placing electrode arrays directly on the surface of the cerebral cortex. The electrodes rest on the brain rather than being inserted into it, making ECoG a middle ground between non-invasive scalp EEG and fully invasive intracortical recording.

Signal Characteristics

ECoG signals have several advantages over scalp EEG:

Spatial resolution: Electrodes can be spaced as closely as 1mm apart (high-density arrays), enabling spatial resolution far exceeding scalp EEG (which integrates activity over ~1 cm²).
Bandwidth: ECoG captures signals up to ~500 Hz, including high-gamma oscillations (70-150 Hz) that are strong correlates of local cortical activation. Scalp EEG attenuates these frequencies.
Signal-to-noise ratio: Without skull and scalp attenuating the signal, ECoG amplitude is 5-10x higher than scalp EEG.
Stability: Surface arrays do not penetrate tissue and therefore avoid the progressive foreign body response affecting intracortical electrodes.

Clinical Use

ECoG is used clinically for pre-surgical epilepsy mapping — strips and grids of electrodes placed on the brain surface during diagnostic monitoring to localize seizure foci. This established clinical procedure has enabled BCI researchers to study high-density ECoG in humans as a secondary use during epilepsy monitoring hospitalizations.

BCI Applications

For BCI, ECoG occupies an attractive space: better signal quality than non-invasive approaches, potentially more stable and less inflammatory than intracortical recording.

Key ECoG BCI devices:

NeuroPace RNS System: 4-electrode ECoG strips for closed-loop responsive neurostimulation in epilepsy. FDA approved.
Precision Neuroscience Layer 7: 1,024-electrode high-density ECoG array for motor cortex BCI; acute intraoperative trials underway.

High-gamma activity (70-150 Hz) recorded by ECoG arrays is particularly informative for BCI decoding of speech, movement, and imagined movement, with performance approaching that of intracortical single-unit recordings in some tasks.