Electrocorticography (ECoG) sits in an important middle ground between non-invasive EEG and fully invasive penetrating electrode arrays. ECoG electrodes are placed directly on the cortical surface, beneath the skull but on top of the brain's protective membranes. This placement bypasses the signal-degrading effects of the skull while avoiding the tissue damage caused by electrodes that penetrate into brain matter.
The signals recorded by ECoG are substantially richer than scalp EEG — offering better spatial resolution, higher bandwidth, and stronger signal-to-noise ratios. Clinically, ECoG has been used for decades during epilepsy surgery to map seizure foci. More recently, researchers have demonstrated remarkable BCI applications: a team at UC San Francisco used ECoG to decode attempted speech in a paralyzed patient, translating neural activity into text at rates approaching normal conversation speed.
Several companies are pursuing ECoG-based BCI products. Precision Neuroscience has developed an ultra-thin cortical interface called the Layer 7 array that can be placed through a small cranial opening without traditional open-brain surgery. The company's approach prioritizes minimal invasiveness while capturing high-quality cortical signals. ECoG's combination of good signal quality and relative safety makes it an attractive middle path for clinical BCI systems intended for long-term daily use. For deeper coverage, see BCIIntel.