ECoG gamma activity during a language task: differentiating expressive and receptive speech areas

Abstract

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.

Direct Physiologic Evidence of a Heteromodal Convergence Region for Proper Naming in Human Left Anterior Temporal Lobe

“…Furthermore, the significance of lowfrequency oscillations in higher cognitive functions are unknown (Canolty and Knight, 2010). The finding of increased ECoG ERBP in the left ATL in a frequency distribution spanning both beta and gamma bands is surprising given previous ECoG lan- guage studies showing increased power at higher frequencies in classical language cortex (Towle et al, 2008;Miller et al, 2011). If power changes predominately occur in the sub-50 Hz range in the left ATL, it is possible that some of the variability of prior ATL fMRI studies results from poor correlation between the BOLD signal and ECoG power at lower frequencies (Ojemann et al, 1997;Devlin et al, 2000).…”

Redefining the role of Broca’s area in speech

“…In contrast, direct intracranial cortical recordings offer a unique opportunity to acquire neural signals with an unprecedented combination of temporal and spatial resolution. Several such studies have implicated the inferior frontal lobe in word production (14)(15)(16)(17)(18)(19), but did not focus on the specific role of Broca's area in production. Conversely, a recent intracranial study was, to our knowledge, the first to focus on Broca's area, finding evidence for lexical, grammatical, and phonological processing (20), but did not examine the processes required for overt word production (phonetic encoding and articulation).…”

Neural correlate of the construction of sentence meaning

“…6-11) and word-level processes (e.g., refs. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, the most distinctive feature of human language is its compositionality: the ability to create and understand complex meanings from novel combinations of words structured into phrases and sentences (27).…”