Linear aspects of transformation from interictal epileptic discharges to BOLD fMRI signals in an animal model of occipital epilepsy |
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Authors: | Mirsattari Seyed M Wang Zheng Ives John R Bihari Frank Leung L Stan Bartha Robert Menon Ravi S |
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Affiliation: | Faculty of Graduate Studies, The University of Western Ontario, London, Canada. |
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Abstract: | Epileptic disorders manifest with seizures and interictal epileptic discharges (IEDs). The hemodynamic changes that accompany IEDs are poorly understood and may be critical for understanding epileptogenesis. Despite a known linear coupling of the neurovascular elements in normal brain tissues, previous simultaneous electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) studies have shown variable correlations between epileptic discharges and blood oxygenation level-dependent (BOLD) response, partly because most previous studies assumed particular hemodynamic properties in normal brain tissue. The occurrence of IEDs in human subjects is unpredictable. Therefore, an animal model with reproducible stereotyped IEDs was developed by the focal injection of penicillin into the right occipital cortex of rats anesthetized with isoflurane. Simultaneous EEG-fMRI was used to study the hemodynamic changes during IEDs. A hybrid of temporal independent component analysis (ICA) of EEG and spatial ICA of fMRI data was used to correlate BOLD fMRI signals with IEDs. A linear autoregression with exogenous input (ARX) model was used to estimate the hemodynamic impulse response function (HIRF) based on the data from simultaneous EEG-fMRI measurement. Changes in the measured BOLD signal from the right primary visual cortex and bilateral visual association cortices were consistently coupled to IEDs. The linear ARX model was applied here to confirm that a linear transform can be used to study the correlation between BOLD signal and its corresponding neural activity in this animal model of occipital epilepsy. |
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Keywords: | Experimental animal models Electroencephalography Epilepsy Interictal epileptic discharges Magnetic resonance imaging Functional magnetic resonance imaging Blood oxygenation level-dependent Independent component analysis General linear model Hemodynamic impulse response function Linear autoregression with exogenous input model |
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