Researchers explore role of ECoG measurement to improve brain mapping technology

Epilepsy and seizures affect nearly 3 million Americans of all ages, with 200,000 new cases of seizures and epilepsy occurring each year. Epilepsy surgery may be performed in patients who have seizures associated with structural brain abnormalities, such as benign brain tumors and cortical dysplasia, malformations of blood vessels, the genetic disorder tuberous sclerosis, and strokes. The goal of epilepsy surgery is to identify an abnormal area of brain cortex from which the seizures originate and remove it without causing any major functional impairment.

In the U.S., it is estimated that in 2009, there were a total of 22,070 new cases of brain and other CNS tumors diagnosed. Gliomas account for 40 percent of all tumors and 78 percent of malignant tumors. In brain tumor surgery, the aim is always to maximize the resection while minimizing the loss of neurological function. Malignant gliomas usually occupy, or are continuous with functional brain tissue, making them difficult to completely resect. The need to preserve functions like language and movement must be balanced with the necessity for maximal tumor resection.

The gold-standard method of determining cortical functional in brain surgery has been electrocortical stimulation (ECS). ECS works by disrupting the normal cortical function to evoke movement or create transient functional disruption.

Researchers at the University of Washington, Seattle, explored the role of broadband electrocorticographic measurement, with the goal of improving the efficacy of brain mapping technology. The results of this study, Real-Time Electrocorticographic Mapping of Eloquent Cortex, will be presented by Kai Miller, PhD, 4:31 to 4:45 pm, Monday, May 3, 2010, during the 78th Annual Meeting of the American Association of Neurological Surgeons in Philadelphia. Co-authors are Adam O. Hebb, MD, and Jeffrey G. Ojemann, MD.

Electrocorticographic (ECoG) recordings were produced using subdural electrodes and SynAmps2 amplifiers, set to sample at 1 kHz and band-pass filter from 0.15 to 200 Hz. Data were collected and processed online at the bedside using software on a laptop computer. A total of 11 patients with epilepsy, awaiting brain surgery, were enrolled in this study.

The efficacy of simple integration of "chi-band" (76-200Hz) change in the ECoG signal was analyzed by implementing a simple band-pass filter, to estimate broadband spectral change. Following a brief (less than 10-second) period to characterize baseline activity, chi-band activity was integrated while the patients performed motor movement commands and/or verb-generation testing.

For the motor movements testing, each patient performed repeated opening and closing of the hand for 3-second periods, alternating with equal periods of rest. Each period was visually cued, for both movement and rest periods. The hand movement was repeated 30 times, but only the first 5 or 15 seconds of movement was used for this analysis. During simple hand movement, primary hand motor areas were clearly identified.

Patients were asked to state verbs in response to nouns that were presented. The exercises spanned 15 to 30 seconds, during which time, brain mapping took place. While performing verb generation, primary mouth motor areas were consistently identified, as were areas consistent with Broca's and auditory speech.

"Our findings were substantiated by ECS in the same patients. Broadband ECoG changes can be captured in real time to identify eloquent cortex. This study demonstrates the existence of a powerful new tool for functional brain mapping in the operative and chronic implant setting and warrants further testing," remarked Dr. Miller.