Abstracts

Rationale: A number of investigators have reported that event-related augmentation of high-gamma activity70-110 Hz on electrocorticography (ECoG) can localize functionally-important brain regions in children and adults with drug-resistant focal epilepsy. Despite the potential utility of this presurgical evaluation method, the hardware setting for data acquisition has rarely been presented in a hands-on manner. Here, we will openly share our techniques with fellow investigators. Methods: We provide a video and hands-on presentation of the hardware settings for our ECoG-based language mapping. Results: Our study has been approved by the Wayne State University Institutional Review Board, and written informed consent is obtained from patients or their guardians. Extraoperative ECoG signals are acquired using Nihon Kohden Neurofax 1100A Digital EEG Acquisition System. The sampling rate is 1,000 Hertz, and the amplifier band pass filter range is 0.016-300 Hertz; thus, event-related modulation of high-gamma activity at 70-110 Hertz can be sufficiently recorded. While awake and comfortably seated with intracranial electrodes in place, each patient is assigned auditory and picture naming tasks at the bedside while extraneous noises are minimized. During the auditory naming task, a hands-free microphone is secured in front of the patient’s mouth as well as in front of a computer speaker which provides auditory question-and-answer trials. Patients are instructed to overtly name a relevant answer for each question trial. For example, the patient could state “Bird” when presented with “What flies in the sky?”.  Sound-wave signals from both the speaker and patient are delivered to the DC input of the EEG acquisition system via Olympus WS823 Digital Voice Recorder. This procedure effectively synchronizes ECoG and sound-wave signals recorded during the tasks, and allows us to denote the exact times of both question onset and offset along with response onset. Likewise, during the picture naming task, a hands-free microphone is given to the patient, and the patient’s speech sounds are delivered to the EEG acquisition system. Each picture stimulus has a small white square in the bottom right corner of the computer screen, and the onset and offset of picture presentation are detected as an increase and decrease of light intensity, respectively, by a photodiode attached to the corner of the LCD monitor. This light intensity information is constantly delivered to the DC input of the EEG acquisition system. Patient participation time ranges from 5 to 15 minutes per task. Conclusions: The aforementioned hardware settings allow us to conduct subsequent time-frequency analyses to determine ‘when’ and ‘where’ in the brain high-gamma activity is augmented during a given task. Clinicians and researchers in epilepsy centers possessing a digital ECoG acquisition system with a sampling rate of ≥400 Hertz can initiate ECoG-based language mapping with a small amount of start-up funding. Funding: NIH grant NS64033 (E. Asano)