Temporal evolution of gamma activity in human cortex during an overt and covert word repetition task

Abstract

Several scientists have proposed different models for cortical processing of speech. Classically, the regions participating in language were thought to be modular with a linear sequence of activations. More recently, modern theoretical models have posited a more hierarchical and distributed interaction of anatomic areas for the various stages of speech processing. Traditional imaging techniques can only define the location or time of cortical activation, which impedes the further evaluation and refinement of these models. In this study, we take advantage of recordings from the surface of the brain [electrocorticography (ECoG)], which can accurately detect the location and timing of cortical activations, to study the time course of ECoG high gamma (HG) modulations during an overt and covert word repetition task for different cortical areas. For overt word production, our results show substantial perisylvian cortical activations early in the perceptual phase of the task that were maintained through word articulation. However, this broad activation is attenuated during the expressive phase of covert word repetition. Across the different repetition tasks, the utilization of the different cortical sites within the perisylvian region varied in the degree of activation dependent on which stimulus was provided (auditory or visual cue) and whether the word was to be spoken or imagined. Taken together, the data support current models of speech that have been previously described with functional imaging. Moreover, this study demonstrates that the broad perisylvian speech network activates early and maintains suprathreshold activation throughout the word repetition task that appears to be modulated by the demands of different conditions.

Spatio-Temporal Progression of Cortical Activity Related to Continuous Overt and Covert Speech Production in a Reading Task

“…In a series of verb generation and picture naming tasks, they found that the area Spt (temporal plane) was involved in the preparation of upcoming speech vocalizations, while classically expressive areas (inferior frontal gyrus, premotor cortex) were silent. Subsequent studies [26–28] confirmed a more general result of STG activations during covert speech production tasks, which support the notion that auditory processes are the primary factor in preparing upcoming speech productions. However, several other studies [21, 22, 25, 34] came to conflicting conclusions in which only the inferior frontal and pre-central cortices are involved in speech preparation with little-to-no involvement from auditory regions.…”

“…In order to make comparisons with prior word repetition studies of overt and covert speech production (e.g., [13, 20, 28, 38]), we utilized visual presentation of the stimulus words on a computer screen that were continuously updated reflecting the subjects’ current position in the larger stimulus paragraph. We obtained ECoG activity from eight human subjects who participated in this continuous word repetition task.…”

Electrocorticographic language mapping in children by high-gamma synchronization during spontaneous conversation: Comparison with conventional electrical cortical stimulation

“…It is known that event-related changes in high-␥ frequency range in ECoG are a biomarker of cortical information processing (Crone et al, 1998(Crone et al, , 2006Leuthardt et al, 2012). This study extends this concept to high-␥ spectral changes related to spontaneous natural conversation, compared to stimulus-response tasks conventionally used for language testing.…”

“…3). These electrode contacts may represent sites participating in, but not crucial for, language function (Cervenka et al, 2013;Leuthardt et al, 2012). For mouth motor control, there is evidence for more extensive cortical networks in prefrontal cortex (Rizzolatti et al, 1998), which may also explain HGS+, ECS− sites.…”

Dynamic Analysis of Naive Adaptive Brain-Machine Interfaces

“…Second, instructed motor imagery may generate patterns of neural activity that differ from patterns elicited at output neurons during closedloop BMI control, resulting in performance degradation (Shenoy, Krauledat, Blankertz, Rao, & Muller, 2006;Taylor, Tillery, & Schwartz, 2002). Third, artificial and natural somatosensory feedback may further distort these observed neural signal patterns relative to instructed motor imagery, such as in the difference between sensorimotor potentials evoked during imagined versus overt arm movements (Miller et al, 2010) or word repetition (Leuthardt et al, 2012) that drive sensory feedback (touch, pressure, proprioception, audition, vision) from the arm, mouth, larynx, eye, and ear. Fourth, learning proficient BMI operation with nonadaptive (static) filters is slow, requiring weeks to months for basic cursor control alone (Ganguly & Carmena, 2009;Wolpaw, McFarland, Neat, & Forneris, 1991).…”