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Abnormal interictal gamma activity may manifest a seizure onset zone in temporal lobe epilepsy.
MedLine Citation:
PMID:  21442774     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
Even though recent studies have suggested that seizures do not occur suddenly and that before a seizure there is a period with an increased probability of seizure occurrence, neurophysiological mechanisms of interictal and pre-seizure states are unknown. The ability of mathematical methods to provide much more sensitive tools for the detection of subtle changes in the electrical activity of the brain gives promise that electrophysiological markers of enhanced seizure susceptibility can be found even during interictal periods when EEG of epilepsy patients often looks 'normal'. Previously, we demonstrated in animals that hippocampal and neocortical gamma-band rhythms (30-100 Hz) intensify long before seizures caused by systemic infusion of kainic acid. Other studies in recent years have also drawn attention to the fast activity (>30 Hz) as a possible marker of epileptogenic tissue. The current study quantified gamma-band activity during interictal periods and seizures in intracranial EEG (iEEG) in 5 patients implanted with subdural grids/intracranial electrodes during their pre-surgical evaluation. In all our patients, we found distinctive (abnormal) bursts of gamma activity with a 3 to 100 fold increase in power at gamma frequencies with respect to selected by clinicians, quiescent, artifact-free, 7-20 min "normal" background (interictal) iEEG epochs 1 to 14 hours prior to seizures. Increases in gamma activity were largest in those channels which later displayed the most intensive electrographic seizure discharges. Moreover, location of gamma-band bursts correlated (with high specificity, 96.4% and sensitivity, 83.8%) with seizure onset zone (SOZ) determined by clinicians. Spatial localization of interictal gamma rhythms within SOZ suggests that the persistent presence of abnormally intensified gamma rhythms in the EEG may be an important tool for focus localization and possibly a determinant of epileptogenesis.
Authors:
Andrei V Medvedev; Anthony M Murro; Kimford J Meador
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  International journal of neural systems     Volume:  21     ISSN:  0129-0657     ISO Abbreviation:  Int J Neural Syst     Publication Date:  2011 Apr 
Date Detail:
Created Date:  2011-03-28     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9100527     Medline TA:  Int J Neural Syst     Country:  Singapore    
Other Details:
Languages:  eng     Pagination:  103-14     Citation Subset:  IM    
Affiliation:
Center for Functional and Molecular Imaging, Department of Neurology Georgetown University, 3900 Reservoir Road, NW, Washington, DC 20057-1488, USA. am236@georgetown.com.
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