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Epilepsy: Electrocorticography (ECoG)

If an epilepsy case is unresponsive to medications, there are alternative, surgical treatments that  may be an option. To determine this, the treating neurologist may obtain magnetic resonance imaging (MRI) and electroencephalography (EEG) over prolonged periods of time to  determine where the seizures are coming from in the brain. Ideally, a surgery can be performed where the portion that is causing the issue can be removed, most commonly the temporal lobe of the brain. A recent alternative to open surgery in this region is laser interstitial thermal therapy (LITT), during which a laser pinpoints and destroys a small part of the brain causing the seizure. When the area causing seizures is outside the temporal lobe, often just that problem area is removed. In children, other options for epilepsy may be performed. This may include: corpus callosotomy where the bundle of nerves connecting the right and left side of the brain is completed or partially severed, hemispherectomy where one side of the outer layer of the brain (cerebral cortex) is removed, and functional hemispherectomy where the side of the brain that induces seizures is disconnected from the other parts of the brain.

Though often the precise area where seizures come from can be identified non-invasively, sometimes it cannot. In these cases, patients may undergo a procedure so that “better” EEG information can be gathered. Often these leads are kept in place for three to seven days to determine the origin of the seizures. These invasive leads are used to perform electrocorticography (ECoG). The leads that detect the seizures may be paddles that face on the brain or cylindrical leads that go into the brain. Sometimes a combination of both are used. The procedures are often called subdural grid placement, depth electrode placement or stereoelectroencephalography (sEEG).

The surgery is several hours long and is most commonly done under general anesthesia. The procedure varies based on what type of paddles or cylindrical leads are placed. The number of leads differs depending on what type of seizures each patient has and the placement of the leads is individualized based on information gathered prior to surgery. The patient will remain in the hospital for three to seven days while the brain is monitored for seizure activity. This may be longer in certain cases if no seizures occur. Seizure medications are often reduced so this can happen. Flashing lights and limited sleep may be needed if seizures still do not occur. The information gathered performs a map of where seizures occur as well as of other important areas in the brain, such as speech and movement. The leads are removed in the operating room. Sometimes the area causing the seizure may be removed at the same time.

  • Arcot Desai S, Tcheng TK, Morrell MJ. Quantitative electrocorticographic biomarkers of clinical outcomes in mesial temporal lobe epileptic patients treated with the RNS® system. Clin Neurophysiol. 2019 Aug;130(8):1364-1374: This study aimed to find ECoG characteristics which predict clinical outcomes in epilespy patients. The study found various characteristics which may be able to provide physicans with an idea of how patients will respond to treatment for epilepsy.

Patient Pages are authored by neurosurgical professionals, with the goal of providing useful information to the public.

Julie G. Pilitsis, MD, PhD
Chair- Neuroscience & Experimental Therapeutics
Professor- Neurosurgery and Neuroscience & Experimental Therapeutics
Albany Medical College

Specialty in neuromodulation with research interests in treatments for movement disorders and chronic pain.

Olga Khazen, BS
Research Coordinator- Neuroscience & Experimental Therapeutics
Albany Medical College

– Include disclaimer:

The AANS does not endorse any treatments, procedures, products or physicians referenced in these patient fact sheets. This information provided is an educational service and is not intended to serve as medical advice. Anyone seeking specific neurosurgical advice or assistance should consult his or her neurosurgeon, or locate one in your area through the AANS’ Find a Board-certified Neurosurgeon online tool.