Technical Approach

Electrocorticography (ECoG) uses electrode grids placed on the brain’s cortical surface, typically positioned subdurally between the dura mater and cortex. The grids contain dozens to hundreds of electrodes spaced millimeters apart, recording population-level neural activity from superficial cortical structures without penetrating brain tissue.

Signal Characteristics

ECoG provides substantially better spatial resolution than scalp EEG while remaining less invasive than intracortical penetrating electrodes. The proximity to cortex enables recording of local field potentials, including high-frequency activity that tracks coordinated neural population firing, without the risk of chronic scarring from embedded electrodes.

Clinical Applications

ECoG has proven particularly valuable for speech neuroprosthetics, with UCSF researchers demonstrating high-accuracy decoding of intended speech from motor cortex ECoG recordings. The approach also enables mapping of seizure-prone brain regions during epilepsy surgery, leveraging the clinical electrode implantation for dual research purposes. In April 2025 the FDA cleared Precision Neuroscience’s Layer 7 cortical surface array under 510(k) for temporary use of less than 30 days.

Surgical Placement

ECoG electrode grids require craniotomy for dural access, a more substantial surgical procedure than noninvasive approaches but less extensive than intracortical penetration. Many ECoG implants are performed during epilepsy surgery, enabling research collaboration with clinical patient populations. Newer designs reduce the opening: Precision Neuroscience inserts its Layer 7 thin-film array through a skull slit under one millimetre wide, and the CEA/Clinatec WIMAGINE implant sits epidurally.

Chronic Limitations

While ECoG avoids intracortical scarring, chronic subdural implantation carries infection and hemorrhage risks. Most ECoG research uses temporary implants (weeks to months), although chronic systems are now in human use: one UCSF BRAVO participant has been enrolled since 2019, and the WIMAGINE epidural implant has more than seven years of human safety data. The grid design also limits spatial resolution compared to intracortical arrays: surface electrodes record pooled field potentials summed across many neurons.