A number of investigators have reported that event-related augmentation of high-gamma activity at 70-110 Hz on electrocorticography (ECoG) can localize functionally-important brain regions in children and adults who undergo epilepsy surgery. The advantages of ECoG-based language mapping over the gold-standard stimulation include: (i) lack of stimulation-induced seizures, (ii) better sensitivity of localization of language areas in young children, and (iii) shorter patient participant time. Despite its potential utility, ECoG-based language mapping is far less commonly practiced than stimulation mapping. Here, we have provided video presentations to explain, point-by-point, our own hardware setting and time-frequency analysis procedures. We also have provided standardized auditory stimuli, in multiple languages, ready to be used for ECoG-based language mapping. Finally, we discussed the technical aspects of ECoG-based mapping, including its pitfalls, to facilitate appropriate interpretation of the data.
People occasionally use filler phrases or pauses, such as "uh", "um", or "y'know," that interrupt the flow of a sentence and fill silent moments between ordinary (non-filler) phrases. It remains unknown which brain networks are engaged during the utterance of fillers. We addressed this question by quantifying event-related cortical high gamma activity at 70-110 Hz. During extraoperative electrocorticography recordings performed as part of the presurgical evaluation, patients with drug-resistant focal epilepsy were instructed to overtly explain, in a sentence, 'what is in the image (subject)', 'doing what (verb)', 'where (location)', and 'when (time)'. Time-frequency analysis revealed that the utterance of fillers, compared to that of ordinary words, was associated with a greater magnitude of high gamma augmentation in association and visual cortex of either hemisphere. Our preliminary results raise the hypothesis that filler utterance would often occur when large-scale networks across the association and visual cortex are engaged in cognitive processing, including lexical retrieval as well as verbal working memory and visual scene scanning. Regardless of age, gender, or native language, healthy individuals use filler phrases, also known as filled pauses, during spontaneous speech 1. Frequent utterance of fillers is tightly associated with increased effort to recall or search for a relevant word 2 , increased anxiety 3 , and divided attention 4. Disfluent non-native speakers compared to native ones as well as dysphasic patients compared to non-dysphasic ones more frequently utter fillers during verbal communication 5,6. Practice and preparation are effective methods to reduce the rate of filler utterance during interviews or presentations because the word recall process becomes more automatic and less effortful 7. What happens in the cerebral cortex when one utters a filler? Only a small number of studies have attempted to determine the neural correlates of filler utterances. Effective study design is a consistent challenge in the field due to the unpredictable timing of naturally occurring filler phrases or pauses. In a study of six healthy adults using functional MRI (fMRI) 8 , participants were instructed to speak whatever came to mind when viewing Rorschach inkblot plates. The authors reported that trials accompanied by overt filler pauses, compared to those accompanied by complete silent pauses, was associated with increased hemodynamic activation in the left superior temporal gyrus. Another fMRI study characterized the spatial pattern of hemodynamic activation when participants listened to other's speeches including fillers to determine the neural correlates of listening and not utterance of fillers 9. Measurement of event-related high gamma activity on electrocorticography (ECoG), a presurgical evaluation method for patients with drug-resistant epilepsy 10 , provides a unique opportunity to quantify the rapid dynamics of human perception and cognition without increasing the risk of surgical complications 11...
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