| Intermittent spatio-temporal desynchronization and sequenced synchrony in ECoG signals. | |
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MedLine Citation:
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PMID: 19045505 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Electrocorticographic (ECoG) signals from the brain surface typically exhibit high synchrony across large cortical areas, interrupted by brief periods of desynchronization exhibiting propagating phase discontinuities, across which spatial patterns of phase emerge in selected frequency bands. Experiments with rabbits trained using classical conditioning paradigms indicated that such desynchronization periods demarcate cognitive processing in the subjects; the ECoG in the frames between such periods revealed spatial patterns of amplitude modulation that were classified with respect to sensory stimuli that the rabbits had been trained to recognize. The present work describes intermittent synchrony and desynchronization of ECoG signals measured over the visual cortex. We analyze the analytic amplitude (AA) and analytic phase (AP) of the signals bandpassed over the beta band (12.5-25 Hz) and theta band (3-7 Hz) using the Hilbert transform. The AP of analytic signals evaluated using a Shannon-based synchronization index in theta band exhibits phase synchronization for varying time periods averaging about 1 s, interrupted by desynchronization periods of duration about 0.1 s. Synchronization periods in the beta-band last <100 ms, with interruptions by desynchronization lasting one-tenth that, in which the analytic amplitude drops drastically. During these "null spikes," the analytic phase is undefined, and the spatial and temporal phase differences show high dispersion. Detailed examination of the bandpass filtered ECoG confirms the presence of a shared mean frequency in a frame of synchronized oscillation, at which frequency the spatial pattern of the AP has the form of a cone. Between frames the AA approaches zero. The form of the null spike resembles a tornado (a vortex), as shown in sequential frames by a rotating spatial pattern of amplitude in the filtered ECoG. |
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Authors:
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Robert Kozma; Walter J Freeman |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Chaos (Woodbury, N.Y.) Volume: 18 ISSN: 1089-7682 ISO Abbreviation: Chaos Publication Date: 2008 Sep |
Date Detail:
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Created Date: 2008-12-02 Completed Date: 2009-01-30 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 100971574 Medline TA: Chaos Country: United States |
Other Details:
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Languages: eng Pagination: 037131 Citation Subset: IM |
Copyright Information:
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(c) 2008 American Institute of Physics. |
Affiliation:
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Computational NeuroDynamics Laboratory, University of Memphis, Memphis, Tennessee 38120, USA. rkozma@memphis.edu |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Animals Biological Clocks / physiology* Computer Simulation Evoked Potentials, Visual / physiology* Models, Neurological* Nerve Net / physiology* Nonlinear Dynamics Rabbits Visual Cortex / physiology* Visual Perception / physiology* |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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