electrocorticography (ECoG)

Electrocorticography, or ECoG, places a thin sheet or grid of electrodes directly on the surface of the brain's wrinkled outer layer, the cortex. The skull is opened in surgery, but the electrodes only rest on the surface — they do not pierce into the tissue. Compared with scalp EEG, it is like moving your microphone from outside the stadium wall to right beside the crowd: the sound becomes far clearer and more detailed.

Because there is no skull in the way, ECoG signals are much sharper and pick up fast, high-frequency activity that scalp EEG simply loses. This richer detail makes it powerful for decoding fine movements and even attempted speech. It sits in a sweet spot — far more informative than EEG, yet less risky than electrodes that penetrate the brain.

The trade-off is that ECoG requires brain surgery, so it is mainly used in people who are already having an operation, such as some patients being mapped before epilepsy surgery. That clinical setting has made ECoG a key testing ground for advanced brain–computer interfaces.