The button-sized ecog electrodes don 't penetrate the brain but detect abnormal electrical activity and allow surgeons to locate and remove a small portion of the brain causing the seizures .
For patients with severe epileptic seizures uncontrolled by medication , surgeons remove part of the skull and place a silicone mat containing ecog electrodes over the brain for days to weeks while the cranium is held in place but not reattached .
These electrodes are known as microecogs because they are a small version of the much larger electrodes used for electrocorticography , or ecog , developed a half century ago .
