Spatiotemporal dynamics of word processing in the human brain

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequ...

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Bibliographic Details
Published in:Frontiers in neuroscience 2007-11, Vol.1 (1), p.185-196
Main Authors: Canolty, Ryan T, Soltani, Maryam, Dalal, Sarang S, Edwards, Erik, Dronkers, Nina F, Nagarajan, Srikantan S, Kirsch, Heidi E, Barbaro, Nicholas M, Knight, Robert T
Format: Article
Language:English
Subjects:
Acoustics
Aphasia
Brain
electrocorticogram
Electrodes
Frequency dependence
Frequency range
gamma
Language
Medical imaging
Neuroscience
Neurosurgery
Nonwords
Onomastics
oscillations
Patients
Phonology
Superior temporal gyrus
Superior temporal sulcus
target detection
Temporal cortex
Temporal gyrus
Verbs
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Summary:We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80-200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior.
ISSN:1662-4548
1662-453X
DOI:10.3389/neuro.01.1.1.014.2007