Original Research Article
Spatiotemporal dynamics of word processing in the human brain
Ryan T. Canolty 1*, Maryam Soltani 1, 2, Sarang S. Dalal 3, Erik Edwards 1, 2, 4, Nina F. Dronkers 5, 6, Srikantan S. Nagarajan 4, Heidi E. Kirsch 7, Nicholas M. Barbaro 8 and Robert T. Knight 1, 2, 7, 8
1 Helen Wills Neuroscience Institute, University of California, USA
2 Department of Psychology, University of California, USA
3 INSERM - Unité 821, Processus mentaux et activation cérébrale Centre Hospitalier Le Vinatier, France
4 Department of Radiology, University of California, USA
5 Center for Aphasia and Related Disorders VANCHCS, USA
6 Department of Neurology, University of California, Davis, USA
7 Department of Neurology, University of California, USA
8 Department of Neurosurgery, University of California, USA
2 Department of Psychology, University of California, USA
3 INSERM - Unité 821, Processus mentaux et activation cérébrale Centre Hospitalier Le Vinatier, France
4 Department of Radiology, University of California, USA
5 Center for Aphasia and Related Disorders VANCHCS, USA
6 Department of Neurology, University of California, Davis, USA
7 Department of Neurology, University of California, USA
8 Department of Neurosurgery, University of California, USA
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.
Keywords: electrocorticogram, oscillations, gamma, verbs, word processing, target detection, superior temporal gyrus, superior temporal sulcus
Copyright: © 2007 Canolty, Soltani, Dalal, Edwards, Dronkers, Nagarajan, Kirsch, Barbaro and Knight. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.
*Correspondence: Ryan T. Canolty, Helen Wills Neuroscience Institute, University of California, Berkeley,132 Barker Hall, Berkeley, CA 94720-3190, USA. e-mail: rcanolty@gmail.com
Citation: Canolty RT, Soltani M, Dalal SS, Edwards E, Dronkers NF, Nagarajan SS, Kirsch HE, Barbaro NM and Knight RT (2007) Spatiotemporal dynamics of word processing in the human brain. Front. Neurosci. 1,1:185-196. doi:10.3389/neuro.01.1.1.014.2007
Received: 15 August 2007; paper pending published: 01 September 2007; accepted: 01 September 2007; published online: 15 October 2007.
Edited by:
Idan Segev, Hebrew University, Israel
Reviewed by:
Michael Kahana, University of Pennsylvania, USA
Nathan Crone, The Johns Hopkins Hospital, USA
Nathan Crone, The Johns Hopkins Hospital, USA
*Correspondence: Ryan T. Canolty, Helen Wills Neuroscience Institute, University of California, Berkeley,132 Barker Hall, Berkeley, CA 94720-3190, USA. e-mail: rcanolty@gmail.com
