Brain Advance Access published online on July 11, 2008
Brain, doi:10.1093/brain/awn147
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ECoG gamma activity during a language task: differentiating expressive and receptive speech areas
1Department of Neurology, 2Department of Surgery, 3Department of Pediatrics, 4Department of Psychiatry, The University of Chicago, Chicago, IL 60637, 5Department of Radiology, The Children's; Hospital of Philadelphia, Philadelphia, PA, 6Center for Functional Brain Imaging, New Mexico VA Healthcare System, Albuquerque, NM and 7Division of Neuroradiology, Department of Imaging Sciences, National Institutes of Health, Bethesda, MD 20892, USA
Correspondence to:
Vernon L. Towle, PhD, Professor of Neurology, Surgery, Pediatrics and Psychiatry, Department of Neurology, MC-2030, The University of Chicago, 5841 S. Maryland Avenue, Chicago, IL 60637, USA E-mail: towle{at}uchicago.edu
Electrocorticographic (ECoG) spectral patterns obtained during language tasks from 12 epilepsy patients (age: 12–44 years) were analysed in order to identify and characterize cortical language areas. ECoG from 63 subdural electrodes (500 Hz/channel) chronically implanted over frontal, parietal and temporal lobes were examined. Two language tasks were performed. During the first language task, patients listened to a series of 50 words preceded by warning tones, and were asked to repeat each word. During a second memory task, subjects heard the 50 words from the first task randomly mixed with 50 new words and were asked to repeat the word only if it was a new word. Increases in ECoG gamma power (70–100 Hz) were observed in response to hearing tones (primary auditory cortex), hearing words (posterior temporal and parietal cortex) and repeating words (lateral frontal and anterior parietal cortex). These findings were compared to direct electrical stimulation and separate analysis of ECoG gamma changes during spontaneous inter-personal conversations. The results indicate that high-frequency ECoG reliably differentiates cortical areas associated with receptive and expressive speech processes for individual patients. Compared to listening to words, greater frontal lobe and decreased temporal lobe gamma activity was observed while speaking. The data support the concept of distributed functionally specific language modules interacting to serve receptive and expressive speech, with frontal lobe ‘corollary discharges’ suppressing low-level receptive cortical language areas in the temporal lobe during speaking.
Key Words: language mapping; cortical mapping; direct cortical stimulation; functional mapping; epilepsy surgery; electrocorticography; ECoG power
Received March 27, 2008. Revised May 14, 2008. Accepted June 13, 2008.