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Ksendzovsky A, Bachani M, Altshuler M, Walbridge S, Mortazavi A, Moyer M, Chen C, Fayed I, Steiner J, Edwards N, Inati SK, Jahanipour J, Maric D, Heiss JD, Kapur J, Zaghloul KA. Chronic neuronal activation leads to elevated lactate dehydrogenase A through the AMP-activated protein kinase/hypoxia-inducible factor-1α hypoxia pathway. Brain Commun 2022; 5:fcac298. [PMID: 36655171 PMCID: PMC9838803 DOI: 10.1093/braincomms/fcac298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 07/11/2022] [Accepted: 11/28/2022] [Indexed: 12/03/2022] Open
Abstract
Recent studies suggest that changes in neuronal metabolism are associated with epilepsy. High rates of ATP depletion, lactate dehydrogenase A and lactate production have all been found in epilepsy patients, animal and tissue culture models. As such, it can be hypothesized that chronic seizures lead to continuing elevations in neuronal energy demand which may lead to an adapted metabolic response and elevations of lactate dehydrogenase A. In this study, we examine elevations in the lactate dehydrogenase A protein as a long-term cellular adaptation to elevated metabolic demand from chronic neuronal activation. We investigate this cellular adaptation in human tissue samples and explore the mechanisms of lactate dehydrogenase A upregulation using cultured neurones treated with low Mg2+, a manipulation that leads to NMDA-mediated neuronal activation. We demonstrate that human epileptic tissue preferentially upregulates neuronal lactate dehydrogenase A, and that in neuronal cultures chronic and repeated elevations in neural activity lead to upregulation of neuronal lactate dehydrogenase A. Similar to states of hypoxia, this metabolic change occurs through the AMP-activated protein kinase/hypoxia-inducible factor-1α pathway. Our data therefore reveal a novel long-term bioenergetic adaptation that occurs in chronically activated neurones and provide a basis for understanding the interplay between metabolism and neural activity during epilepsy.
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Affiliation(s)
- Alexander Ksendzovsky
- Department of Neurosurgery, School of Medicine, University of Maryland, Baltimore, MD 21201, USA,Surgical Neurology Branch, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA,Department of Neurological Surgery, University of Virginia Health System, University of Virginia, Charlottesville, VA 22903, USA
| | | | | | | | - Armin Mortazavi
- Surgical Neurology Branch, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA
| | - Mitchell Moyer
- Department of Neurosurgery, School of Medicine, University of Maryland, Baltimore, MD 21201, USA
| | - Chixiang Chen
- Department of Neurosurgery, School of Medicine, University of Maryland, Baltimore, MD 21201, USA
| | - Islam Fayed
- Surgical Neurology Branch, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA
| | - Joseph Steiner
- Department of Neurological Surgery, University of Virginia Health System, University of Virginia, Charlottesville, VA 22903, USA
| | - Nancy Edwards
- Surgical Neurology Branch, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA
| | - Sara K Inati
- Office of the Clinical Director, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA
| | - Jahandar Jahanipour
- Flow and Cytometry Core, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda MD, 20892, USA
| | - Dragan Maric
- Flow and Cytometry Core, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda MD, 20892, USA
| | - John D Heiss
- Surgical Neurology Branch, National Institute of Neurologic Disorders and Stroke, National Institute of Health, Bethesda, MD 20892, USA
| | - Jaideep Kapur
- Department of Neurology, University of Virginia Health System, University of Virginia, Charlottesville, VA 22903, USA,Neuroscience Department, University of Virginia Health System, University of Virginia, Charlottesville, VA 22903, USA
| | - Kareem A Zaghloul
- Correspondence to: Kareem A. Zaghloul Surgical Neurology Branch, NINDS National Institutes of Health Building 10, Room 3D20 10 Center Drive, Bethesda, MD 20892-1414, USA E-mail:
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Kraljič A, Matkovič A, Purg N, Demšar J, Repovš G. Evaluation and comparison of most prevalent artifact reduction methods for EEG acquired simultaneously with fMRI. FRONTIERS IN NEUROIMAGING 2022; 1:968363. [PMID: 37555133 PMCID: PMC10406266 DOI: 10.3389/fnimg.2022.968363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 08/02/2022] [Indexed: 08/10/2023]
Abstract
Multimodal neuroimaging using EEG and fMRI provides deeper insights into brain function by improving the spatial and temporal resolution of the acquired data. However, simultaneous EEG-fMRI inevitably compromises the quality of the EEG and fMRI signals due to the high degree of interaction between the two systems. Fluctuations in the magnetic flux flowing through the participant and the EEG system, whether due to movement within the magnetic field of the scanner or to changes in magnetic field strength, induce electrical potentials in the EEG recordings that mask the much weaker electrical activity of the neuronal populations. A number of different methods have been proposed to reduce MR artifacts. We present an overview of the most commonly used methods and an evaluation of the methods using three sets of diverse EEG data. We limited the evaluation to open-access and easy-to-use methods and a reference signal regression method using a set of six carbon-wire loops (CWL), which allowed evaluation of their added value. The evaluation was performed by comparing EEG signals recorded outside the MRI scanner with artifact-corrected EEG signals recorded simultaneously with fMRI. To quantify and evaluate the quality of artifact reduction methods in terms of the spectral content of the signal, we analyzed changes in oscillatory activity during a resting-state and a finger tapping motor task. The quality of artifact reduction in the time domain was assessed using data collected during a visual stimulation task. In the study we utilized hierarchical Bayesian probabilistic modeling for statistical inference and observed significant differences between the evaluated methods in the success of artifact reduction and associated signal quality in both the frequency and time domains. In particular, the CWL system proved superior to the other methods evaluated in improving spectral contrast in the alpha and beta bands and in recovering visual evoked responses. Based on the results of the evaluation study, we proposed guidelines for selecting the optimal method for MR artifact reduction.
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Affiliation(s)
- Aleksij Kraljič
- Department of Psychology, Faculty of Arts, University of Ljubljana, Ljubljana, Slovenia
| | - Andraž Matkovič
- Department of Psychology, Faculty of Arts, University of Ljubljana, Ljubljana, Slovenia
| | - Nina Purg
- Department of Psychology, Faculty of Arts, University of Ljubljana, Ljubljana, Slovenia
| | - Jure Demšar
- Department of Psychology, Faculty of Arts, University of Ljubljana, Ljubljana, Slovenia
- Faculty of Computer and Information Science, University of Ljubljana, Ljubljana, Slovenia
| | - Grega Repovš
- Department of Psychology, Faculty of Arts, University of Ljubljana, Ljubljana, Slovenia
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Ur Özçelik E, Kurt E, Şirin NG, Eryürek K, Ulaşoglu Yıldız Ç, Harı E, Ay U, Bebek N, Demiralp T, Baykan B. Functional connectivity disturbances of ascending reticular activating system and posterior thalamus in juvenile myoclonic epilepsy in relation with photosensitivity: A resting-state fMRI study. Epilepsy Res 2021; 171:106569. [PMID: 33582535 DOI: 10.1016/j.eplepsyres.2021.106569] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2020] [Revised: 12/29/2020] [Accepted: 02/01/2021] [Indexed: 10/22/2022]
Abstract
OBJECTIVE Juvenile myoclonic epilepsy (JME) is typified by the occurrence of myoclonic seizures after awakening, though another common trait is myoclonic seizures triggered by photic stimulation. We aimed to investigate the functional connectivity (FC) of nuclei in the ascending reticular activating system (ARAS), thalamus and visual cortex in JME with and without photosensitivity. METHODS We examined 29 patients with JME (16 photosensitive (PS), 13 non- photosensitive-(NPS)) and 28 healthy controls (HCs) using resting-state functional magnetic resonance imaging (rs-fMRI). Seed-to-voxel FC analyses were performed using 25 seeds, including the thalamus, visual cortex, and ARAS nuclei. RESULTS Mesencephalic reticular formation seed revealed significant hyperconnectivity between the bilateral paracingulate gyrus and anterior cingulate cortex in JME group, and in both JME-PS and JME-NPS subgroups compared to HCs (pFWE-corr < 0.001; pFWE-corr < 0.001; pFWE-corr = 0.002, respectively). Locus coeruleus seed displayed significant hyperconnectivity with the bilateral lingual gyri, intracalcarine cortices, occipital poles and left occipital fusiform gyrus in JME-PS group compared to HCs (pFWE-corr <0.001). Additionally, locus coeruleus seed showed significant hyperconnectivity in JME-PS group compared to JME-NPS group with a cluster corresponding to the bilateral lingual gyri and right intracalcarine cortex (pFWE-corr < 0.001). Lastly, the right posterior nuclei of thalamus revealed significant hyperconnectivity with the right superior lateral occipital cortex in JME-PS group compared to HCs (pFWE-corr < 0.002). CONCLUSIONS In JME, altered functional connectivity of the arousal networks might contribute to the understanding of myoclonia after awakening, whereas increased connectivity of posterior thalamus might explain photosensitivity.
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Affiliation(s)
- Emel Ur Özçelik
- Departments of Neurology and Clinical Neurophysiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad, 34093, Istanbul, Turkey; Department of Neurology, Istanbul Bakirkoy Prof. Dr. Mazhar Osman Research and Training Hospital for Psychiatry, Neurology, Neurosurgery, University of Health Sciences, Zuhuratbaba Mahallesi, Dr. Tevfik Sağlam Cad. 25/2, 34147, Bakırkoy, Istanbul, Turkey.
| | - Elif Kurt
- Department of Neuroscience, Aziz Sancar Institute of Experimental Medicine, Istanbul University, Millet Cad, 34093, Çapa, Istanbul, Turkey.
| | - Nermin Görkem Şirin
- Departments of Neurology and Clinical Neurophysiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad, 34093, Istanbul, Turkey.
| | - Kardelen Eryürek
- Department of Neuroscience, Aziz Sancar Institute of Experimental Medicine, Istanbul University, Millet Cad, 34093, Çapa, Istanbul, Turkey; Hulusi Behçet Life Sciences Research Laboratory, Neuroimaging Unit, Istanbul University, Millet Cad, 34093, Capa, Istanbul, Turkey.
| | - Çiğdem Ulaşoglu Yıldız
- Hulusi Behçet Life Sciences Research Laboratory, Neuroimaging Unit, Istanbul University, Millet Cad, 34093, Capa, Istanbul, Turkey.
| | - Emre Harı
- Department of Neuroscience, Aziz Sancar Institute of Experimental Medicine, Istanbul University, Millet Cad, 34093, Çapa, Istanbul, Turkey; Hulusi Behçet Life Sciences Research Laboratory, Neuroimaging Unit, Istanbul University, Millet Cad, 34093, Capa, Istanbul, Turkey.
| | - Ulaş Ay
- Department of Neuroscience, Aziz Sancar Institute of Experimental Medicine, Istanbul University, Millet Cad, 34093, Çapa, Istanbul, Turkey; Hulusi Behçet Life Sciences Research Laboratory, Neuroimaging Unit, Istanbul University, Millet Cad, 34093, Capa, Istanbul, Turkey.
| | - Nerses Bebek
- Departments of Neurology and Clinical Neurophysiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad, 34093, Istanbul, Turkey.
| | - Tamer Demiralp
- Hulusi Behçet Life Sciences Research Laboratory, Neuroimaging Unit, Istanbul University, Millet Cad, 34093, Capa, Istanbul, Turkey; Department of Physiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad, 34093, Capa, Istanbul, Turkey.
| | - Betül Baykan
- Departments of Neurology and Clinical Neurophysiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad, 34093, Istanbul, Turkey.
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Poleon S, Szaflarski JP. Photosensitivity in generalized epilepsies. Epilepsy Behav 2017; 68:225-233. [PMID: 28215998 DOI: 10.1016/j.yebeh.2016.10.040] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 10/26/2016] [Accepted: 10/29/2016] [Indexed: 11/24/2022]
Abstract
Photosensitivity, which is the hallmark of photosensitive epilepsy (PSE), is described as an abnormal EEG response to visual stimuli known as a photoparoxysmal response (PPR). The PPR is a well-recognized phenomenon, occurring in 2-14% of patients with epilepsy but its pathophysiology is not clearly understood. PPR is electrographically described as 2-5Hz spike, spike-wave, or slow wave complexes with frontal and paracentral prevalence. Diagnosis of PPR is confirmed using intermittent photic stimulation (IPS) as well as video monitoring. The PPR can be elicited by certain types of visual stimuli including flicker, high contrast gratings, moving patterns, and rapidly modulating luminance patterns which may be encountered during e.g., watching television, playing video games, or attending discotheques. Photosensitivity may present in different idiopathic (genetic) epilepsy syndromes e.g. juvenile myoclonic epilepsy (JME) as well as non-IGE syndromes e.g. severe myoclonic epilepsy of infancy. Consequently, PPR is present in patients with diverse seizure types including absence, myoclonic, and generalized tonic-clonic (GTC) seizures. Across syndromes, abnormalities in structural connectivity, functional connectivity, cortical excitability, cortical morphology, and behavioral and neuropsychological function have been reported. Treatment of photosensitivity includes antiepileptic drug administration, and the use of non-pharmacological agents, e.g. tinted or polarizing glasses, as well as occupational measures, e.g. avoidance of certain stimuli.
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Affiliation(s)
- Shervonne Poleon
- University of Alabama at Birmingham, Department of Neurology and UAB Epilepsy Center, Birmingham, AL, USA.
| | - Jerzy P Szaflarski
- University of Alabama at Birmingham, Department of Neurology and UAB Epilepsy Center, Birmingham, AL, USA
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5
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Affiliation(s)
- Chang-Hoon Cho
- School of Biosystem and Biomedical Science, College of Health Science, Korea University Seoul, South Korea
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Affiliation(s)
- Lanny Y. Xue
- Department of Neurology Albany Medical Center Albany, New York
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Abstract
Electroencephalography (EEG) has been used to study and characterize epilepsy for decades, but has a limited ability to localize epileptiform activity to a specific brain region. With recent technological advances, high-quality EEG can now be recorded during functional magnetic resonance imaging (fMRI), which characterizes brain activity through local changes in blood oxygenation. By combining these techniques, the specific timing of interictal events can be identified on the EEG at millisecond resolution and spatially localized with fMRI at millimeter resolution. As a result, simultaneous EEG-fMRI provides the opportunity to better investigate the spatiotemporal mechanisms of the generation of epileptiform activity in the brain. This article discusses the technical considerations and their solutions for recording simultaneous EEG-fMRI and the results of studies to date. It also addresses the application of EEG-fMRI to epilepsy in humans, including clinical applications and ongoing challenges.
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Perry G, Brindley LM, Muthukumaraswamy SD, Singh KD, Hamandi K. Evidence for increased visual gamma responses in photosensitive epilepsy. Epilepsy Res 2014; 108:1076-86. [DOI: 10.1016/j.eplepsyres.2014.04.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Revised: 04/05/2014] [Accepted: 04/27/2014] [Indexed: 10/25/2022]
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Bartolini E, Pesaresi I, Fabbri S, Cecchi P, Giorgi FS, Sartucci F, Bonuccelli U, Cosottini M. Abnormal response to photic stimulation in Juvenile Myoclonic Epilepsy: An EEG-fMRI study. Epilepsia 2014; 55:1038-47. [DOI: 10.1111/epi.12634] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/19/2014] [Indexed: 12/01/2022]
Affiliation(s)
- Emanuele Bartolini
- Department of Clinical and Experimental Medicine; University of Pisa; Italy
| | | | - Serena Fabbri
- Department of Clinical and Experimental Medicine; University of Pisa; Italy
| | - Paolo Cecchi
- Department of Clinical and Experimental Medicine; University of Pisa; Italy
| | | | | | - Ubaldo Bonuccelli
- Department of Clinical and Experimental Medicine; University of Pisa; Italy
| | - Mirco Cosottini
- Department of Translational Research and New Technologies in Medicine and Surgery; University of Pisa; Pisa Italy
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Italiano D, Ferlazzo E, Gasparini S, Spina E, Mondello S, Labate A, Gambardella A, Aguglia U. Generalized versus partial reflex seizures: a review. Seizure 2014; 23:512-20. [PMID: 24766826 DOI: 10.1016/j.seizure.2014.03.014] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Accepted: 03/24/2014] [Indexed: 11/30/2022] Open
Abstract
In this review we assess our currently available knowledge about reflex seizures with special emphasis on the difference between "generalized" reflex seizures induced by visual stimuli, thinking, praxis and language tasks, and "focal" seizures induced by startle, eating, music, hot water, somatosensory stimuli and orgasm. We discuss in particular evidence from animal, clinical, neurophysiological and neuroimaging studies supporting the concept that "generalized" reflex seizures, usually occurring in the setting of IGE, should be considered as focal seizures with quick secondary generalization. We also review recent advances in genetic and therapeutic approach of reflex seizures.
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Affiliation(s)
- Domenico Italiano
- Department of Clinical and Experimental Medicine, University of Messina, Italy
| | - Edoardo Ferlazzo
- Department of Medical and Surgical Sciences, Magna Graecia University, Catanzaro, Italy; Regional Epilepsy Centre, Bianchi-Melacrino-Morelli Hospital, Reggio Calabria, Italy.
| | - Sara Gasparini
- Department of Medical and Surgical Sciences, Magna Graecia University, Catanzaro, Italy
| | - Edoardo Spina
- Department of Clinical and Experimental Medicine, University of Messina, Italy
| | | | - Angelo Labate
- Department of Medical and Surgical Sciences, Magna Graecia University, Catanzaro, Italy
| | - Antonio Gambardella
- Department of Medical and Surgical Sciences, Magna Graecia University, Catanzaro, Italy; National Research Council, Piano Lago di Mangone, Cosenza, Italy
| | - Umberto Aguglia
- Department of Medical and Surgical Sciences, Magna Graecia University, Catanzaro, Italy; Regional Epilepsy Centre, Bianchi-Melacrino-Morelli Hospital, Reggio Calabria, Italy
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Jackson GD, Badawy R, Gotman J. Functional magnetic resonance imaging: focus localization. HANDBOOK OF CLINICAL NEUROLOGY 2012; 107:369-85. [PMID: 22938983 DOI: 10.1016/b978-0-444-52898-8.00023-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- Graeme D Jackson
- Department of Neurology, Austin Health, Heidelberg, Victoria, Australia.
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Szabó CÁ, Salinas FS, Narayana S. Functional PET Evaluation of the Photosensitive Baboon. Open Neuroimag J 2011; 5:206-15. [PMID: 22276085 PMCID: PMC3257183 DOI: 10.2174/1874440001105010206] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Revised: 02/03/2011] [Accepted: 02/14/2011] [Indexed: 11/22/2022] Open
Abstract
The baboon provides a unique, natural model of epilepsy in nonhuman primates. Additionally, photosensitivity of the epileptic baboon provides an important window into the mechanism of human idiopathic generalized epilepsies. In order to better understand the networks underlying this model, our group utilized functional positron emission tomography (PET) to compare cerebral blood flow (CBF) changes occurring during intermittent light stimulation (ILS) and rest between baboons photosensitive, epileptic (PS) and asymptomatic, control (CTL) animals. Our studies utilized subtraction and covariance analyses to evaluate CBF changes occurring during ILS across activation and resting states, but also evaluated CBF correlations with ketamine doses and interictal epileptic discharge (IED) rate during the resting state. Furthermore, our group also assessed the CBF responses related to variation of ILS in PS and CTL animals. CBF changes in the subtraction and covariance analyses reveal the physiological response and visual connectivity in CTL animals and pathophysiological networks underlying responses associated with the activation of ictal and interictal epileptic discharges in PS animals. The correlation with ketamine dose is essential to understanding differences in CBF responses between both groups, and correlations with IED rate provides an insight into an epileptic network independent of visual activation. Finally, the ILS frequency dependent changes can help develop a framework to study not only spatial connectivity but also the temporal sequence of regional activations and deactivations related to ILS. The maps generated by the CBF analyses will be used to target specific nodes in the epileptic network for electrophysiological evaluation using intracranial electrodes.
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Affiliation(s)
- C Ákos Szabó
- South Texas Comprehensive Epilepsy Center, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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Moeller F, Siebner HR, Ahlgrimm N, Wolff S, Muhle H, Granert O, Boor R, Jansen O, Gotman J, Stephani U, Siniatchkin M. fMRI activation during spike and wave discharges evoked by photic stimulation. Neuroimage 2009; 48:682-95. [DOI: 10.1016/j.neuroimage.2009.07.019] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Revised: 07/09/2009] [Accepted: 07/10/2009] [Indexed: 11/29/2022] Open
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Voxel-based morphometry evaluation of patients with photosensitive juvenile myoclonic epilepsy. Epilepsy Res 2009; 86:138-45. [DOI: 10.1016/j.eplepsyres.2009.05.016] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2009] [Revised: 05/26/2009] [Accepted: 05/31/2009] [Indexed: 12/15/2022]
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15
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Vaudano AE, Laufs H, Kiebel SJ, Carmichael DW, Hamandi K, Guye M, Thornton R, Rodionov R, Friston KJ, Duncan JS, Lemieux L. Causal hierarchy within the thalamo-cortical network in spike and wave discharges. PLoS One 2009; 4:e6475. [PMID: 19649252 PMCID: PMC2715100 DOI: 10.1371/journal.pone.0006475] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 06/25/2009] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Generalised spike wave (GSW) discharges are the electroencephalographic (EEG) hallmark of absence seizures, clinically characterised by a transitory interruption of ongoing activities and impaired consciousness, occurring during states of reduced awareness. Several theories have been proposed to explain the pathophysiology of GSW discharges and the role of thalamus and cortex as generators. In this work we extend the existing theories by hypothesizing a role for the precuneus, a brain region neglected in previous works on GSW generation but already known to be linked to consciousness and awareness. We analysed fMRI data using dynamic causal modelling (DCM) to investigate the effective connectivity between precuneus, thalamus and prefrontal cortex in patients with GSW discharges. METHODOLOGY AND PRINCIPAL FINDINGS We analysed fMRI data from seven patients affected by Idiopathic Generalized Epilepsy (IGE) with frequent GSW discharges and significant GSW-correlated haemodynamic signal changes in the thalamus, the prefrontal cortex and the precuneus. Using DCM we assessed their effective connectivity, i.e. which region drives another region. Three dynamic causal models were constructed: GSW was modelled as autonomous input to the thalamus (model A), ventromedial prefrontal cortex (model B), and precuneus (model C). Bayesian model comparison revealed Model C (GSW as autonomous input to precuneus), to be the best in 5 patients while model A prevailed in two cases. At the group level model C dominated and at the population-level the p value of model C was approximately 1. CONCLUSION Our results provide strong evidence that activity in the precuneus gates GSW discharges in the thalamo-(fronto) cortical network. This study is the first demonstration of a causal link between haemodynamic changes in the precuneus -- an index of awareness -- and the occurrence of pathological discharges in epilepsy.
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Affiliation(s)
- Anna E Vaudano
- Department of Neurology, Policlinico Umberto I, University of Rome La Sapienza, Rome, Italy
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Moeller F, Siebner HR, Wolff S, Muhle H, Granert O, Jansen O, Stephani U, Siniatchkin M. Mapping brain activity on the verge of a photically induced generalized tonic-clonic seizure. Epilepsia 2009; 50:1632-7. [PMID: 19400879 DOI: 10.1111/j.1528-1167.2009.02011.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In a photosensitive patient intermittent photic stimulation (IPS) accidentally provoked a generalized tonic-clonic seizure during simultaneous recordings of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Before seizure onset, IPS consistently induced generalized photoparoxysmal responses (PPRs). These PPRs were associated with increases in blood oxygen level dependent (BOLD) signal in the visual cortex, the thalamus, and both superior colliculi, and a decrease in BOLD signal in the frontoparietal areas. The BOLD signal in the visual cortex increased in magnitude during consecutive epochs of IPS associated with PPRs. We propose that repeated IPS led to an excessive amount of neuronal activity in the visual cortex that evoked PPRs and finally exceeded a critical threshold and triggered a generalized seizure.
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Affiliation(s)
- Friederike Moeller
- Department of Neuropediatrics, Christian-Albrechts-University, Kiel, Germany.
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Abstract
Photic stimulation is part of a typical EEG in most countries, especially to check on the photoparoxysmal response (PPR). Interest in this response was enhanced in 1997 when hundreds of Japanese children had attacks while viewing a TV cartoon called "Pokemon." The overall prevalence of the PPR among patients requiring an EEG is approximately 0.8%, but 1.7% in children and 8.87% in patients with epilepsy, more often in Caucasians and females. Autosomal dominant inheritance is indicated, and this response is seen especially at the wavelength of 700 nm or at the flicker frequency of 15-18 Hz. The PPR extending beyond the stimulus carries no increased risk of seizures. Prognosis is generally good, especially after 20 years of age. Attention to PPR has been increased with the advent of video games, and the evoked seizures from these games are likely a manifestation of photosensitive epilepsy. Drug therapy has emphasized valproic acid, but Levetiracetam has also been successful in eliminating the PPR.
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Affiliation(s)
- John R Hughes
- Department of Neurology, University of Illinois, Medical Center at Chicago, Illinois 60612, USA.
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Abstract
The application of functional magnetic resonance imaging (fMRI) to elucidation of seizures and epilepsy has been built primarily upon a framework derived from cortical responses to periodic sensory (and cognitive) stimuli. This analytical approach relies upon assumptions that may be less applicable to the problem of seizure origination. Because of the heterogeneous and complex nature of seizures, a number of quantitative methodologies have been derived to understand fMRI changes that are associated with epileptiform neural activity. Separated broadly, these can be divided into those making some set of assumptions about the form of the MRI signal response to neural activation (the general linear model), and those that are data driven. It is likely that a combination of methodologies, where data driven methods are "informed" by knowledge of the underlying neurobiological process will provide the greatest insight into the underlying neurobiological basis of seizure origination.
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Affiliation(s)
- Bart P Keogh
- Section of Neuroradiology, Department of Radiology, University of Washington, Seattle, Washington 98195, USA.
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Szabó CA, Narayana S, Kochunov PV, Franklin C, Knape K, Davis MD, Fox PT, Leland MM, Williams JT. PET imaging in the photosensitive baboon: case-controlled study. Epilepsia 2007; 48:245-53. [PMID: 17295617 DOI: 10.1111/j.1528-1167.2006.00949.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
PURPOSE The baboon (Papio hamadryas spp) offers a natural primate animal model of photosensitive generalized epilepsy. This study compared changes in cerebral blood flow (CBF) during intermittent light stimulation (ILS) between photosensitive and asymptomatic baboons. METHODS Six photosensitive, epileptic (PS) and four nonphotosensitive, asymptomatic (CTL) baboons, matched for age, gender, and weight, were selected based on previous scalp EEG evaluation. Continuous intravenous ketamine (5-13 mg/kg) was used for sedation. Subjects underwent five sequential blood-flow PET studies within 60 min with 20 mCi (15)O-labeled water. Images were acquired in 3D mode (CTI/Siemens HR+ scanner, 63 contiguous slices, 2.4-mm thickness). Three resting scans were alternated with two activation scans during ILS. ILS was performed at 25 Hz for 60 s before to 60 s after the start of an activation scan. PET images were coregistered with MRI (3T Siemens Trio, T(1)-weighted 3D Turboflash sequence; TE/TR/TI, 3.04/2,100/785 ms; flip angle, 13 degrees). PET scans were reviewed and corrected for motion artifact. Resting scans were contrasted with activation scans and averaged independently for both groups. Quantitative CBF analyses were performed for the occipital and motor cortices. RESULTS The CTL baboons showed greatest ILS-induced activation in the left middle frontal and inferior temporal gyri, left brainstem structures and right postcentral gyrus, bilateral occipital lobes, and in the posterior cingulate gyrus and cerebellum. In contrast, the PS animals showed strongest ILS activation in the right anterior cingulate and medial orbital gyri, amygdala, globus pallidum, and left inferior and superior temporal gyri. A striking finding was the absence of occipital and variable motor cortex activation in the PS animals. Deactivations were noted in the right orbitofrontal and anterior cingulate cortices in the CTL baboons and in the posterior cingulate gyrus, brainstem and cerebellum of the PS animals. CONCLUSIONS The patterns of ILS-induced CBF changes differed between CTL and PS groups. These differences of activations and inhibitions suggest involvement of specific cortical-subcortical or networks in photosensitivity.
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Affiliation(s)
- C Akos Szabó
- South Texas Comprehensive Epilepsy Center, University of Texas Health Science Center at San Antonio, Texas 78284-7883, USA.
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20
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Giove F, Garreffa G, Peca S, Carní M, Macrì MA, Di Bonaventura C, Vaudano AE, Giallonardo AT, Prencipe M, Bozzao L, Pantano P, Colonnese C, Maraviglia B. Metabolic alteration transients during paroxysmal activity in an epileptic patient with fixation-off sensitivity: a case study. Magn Reson Imaging 2006; 24:373-9. [PMID: 16677943 DOI: 10.1016/j.mri.2005.11.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2005] [Accepted: 11/21/2005] [Indexed: 11/28/2022]
Abstract
The purpose of this study was to investigate short-time metabolic variations related to continuous epileptic activity elicited by fixation-off sensitivity (FOS). Time-resolved magnetic resonance spectroscopy was performed on a patient on whom previous clinical findings clearly indicated presence of FOS. The epileptic focus was localized with a simultaneous electroencephalographic and functional magnetic resonance imaging study. The results showed a linear increase of the sum of glutamate and glutamine with time of paroxysmal activity in epileptic focus and much greater concentration of choline-containing compounds in focus than in the contralateral side.
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Affiliation(s)
- Federico Giove
- Museo storico della fisica e Centro di studi e ricerche Enrico Fermi, 00184 Rome, Italy
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21
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Gotman J, Kobayashi E, Bagshaw AP, Bénar CG, Dubeau F. Combining EEG and fMRI: A multimodal tool for epilepsy research. J Magn Reson Imaging 2006; 23:906-20. [PMID: 16649203 DOI: 10.1002/jmri.20577] [Citation(s) in RCA: 207] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Patients with epilepsy often present in their electroencephalogram (EEG) short electrical potentials (spikes or spike-wave bursts) that are not accompanied by clinical manifestations but are of important diagnostic significance. They result from a population of abnormally hyperactive and hypersynchronous neurons. It is not easy to determine the location of the cerebral generators and the other brain regions that may be involved as a result of this abnormal activity. The possibility to combine EEG recording with functional MRI (fMRI) scanning opens the opportunity to uncover the regions of the brain showing changes in the fMRI signal in response to epileptic spikes seen in the EEG. These regions are presumably involved in the abnormal neuronal activity at the origin of epileptic discharges. This paper reviews the methodology involved in performing such studies, particularly the challenge of recording a good quality EEG inside the MR scanner while scanning is taking place, and the methods required for the statistical analysis of the combined EEG and fMRI time series. We review the results obtained in patients with different types of epileptic disorders and discuss the difficult theoretical problems raised by the interpretation of an increase (activation) and decrease (deactivation) in blood oxygen level dependent (BOLD) signal, both frequently seen in response to spikes.
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Affiliation(s)
- Jean Gotman
- Montreal Neurological Institute and Hospital, McGill University, Montréal, Québec, Canada.
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22
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Bagshaw AP, Hawco C, Bénar CG, Kobayashi E, Aghakhani Y, Dubeau F, Pike GB, Gotman J. Analysis of the EEG-fMRI response to prolonged bursts of interictal epileptiform activity. Neuroimage 2004; 24:1099-112. [PMID: 15670687 DOI: 10.1016/j.neuroimage.2004.10.010] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2004] [Revised: 07/22/2004] [Accepted: 10/07/2004] [Indexed: 11/17/2022] Open
Abstract
The use of combined EEG-fMRI to study interictal epileptiform activity is increasing and has great potential as a clinical tool, but the haemodynamic response to epileptiform activity remains incompletely characterised. To this end, 19 data sets from 14 patients with prolonged bursts of focal or generalised interictal epileptiform activity lasting up to 15 s were analysed. To determine whether the inclusion of the durations of the epileptic events in the general linear model resulted in increased statistical significance of activated regions, statistical maps were generated with and without the event durations. The mean differences when including the durations were a 14.5% increase in peak t value and a 29.5% increase in volume of activation. This suggests that when analysing EEG-fMRI data from patients with prolonged bursts of interictal epileptiform activity, it is better to include the event durations. To determine whether the amplitudes and latencies of the measured responses were consistent with the general linear model, the haemodynamic response functions for bursts of different durations were calculated and compared with the model predictions. The measured amplitude of the response to the shortest duration events was consistently larger than predicted, which is consistent with studies in normal subjects. For the two data sets with the widest range of event durations, the measured amplitudes increased with the durations of the events without evidence of the plateau that was expected from the general linear model. There were no consistent differences between the measured and modelled latencies.
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Affiliation(s)
- Andrew P Bagshaw
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Room 786, 3801 University Street, Montréal, Québec, Canada H3A 2B4.
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Rubboli G, Parra J, Seri S, Takahashi T, Thomas P. EEG Diagnostic Procedures and Special Investigations in the Assessment of Photosensitivity. Epilepsia 2004; 45 Suppl 1:35-9. [PMID: 14706044 DOI: 10.1111/j.0013-9580.2004.451002.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photosensitivity can be assessed in laboratory conditions with different methods. The most common procedure is intermittent photic stimulation (IPS), whose effectiveness in detecting photosensitivity depends largely on methodologic aspects. Although IPS is a widespread and routinely used procedure in EEG laboratories, only recently has a standardization of the IPS method been proposed. Furthermore, other modalities of visual stimulation, including pattern stimulation and low-luminance visual stimulation (LLVS), have proven their usefulness in detecting photosensitivity. We provide an overview of the methodologic aspects and clinical implications of these procedures, resulting from recent consensus meetings, and the diagnostic usefulness of the LLVS technique in photosensitive individuals whose seizures are triggered particularly by television images. Finally, we briefly illustrate the potential of advanced neurophysiological (magnetoencephalography and high-density EEG) and functional imaging techniques in the investigation of the pathophysiologic mechanisms underlying photosensitivity.
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Affiliation(s)
- Guido Rubboli
- Department of Neurological Sciences, University of Bologna, Bellaria Hospital, Bologna, Italy.
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24
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Salek-Haddadi A, Friston KJ, Lemieux L, Fish DR. Studying spontaneous EEG activity with fMRI. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 2003; 43:110-33. [PMID: 14499465 DOI: 10.1016/s0165-0173(03)00193-0] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The multifaceted technological challenge of acquiring simultaneous EEG-correlated fMRI data has now been met and the potential exists for mapping electrophysiological activity with unprecedented spatio-temporal resolution. Work has already begun on studying a host of spontaneous EEG phenomena ranging from alpha rhythm and sleep patterns to epileptiform discharges and seizures, with far reaching clinical implications. However, the transformation of EEG data into linear models suitable for voxel-based statistical hypothesis testing is central to the endeavour. This in turn is predicated upon a number of assumptions regarding the manner in which the generators of EEG phenomena may engender changes in the blood oxygen level dependent (BOLD) signal. Furthermore, important limitations are posed by a set of considerations quite unique to 'paradigmless fMRI'. Here, these issues are assembled and explored to provide an overview of progress made and unresolved questions, with an emphasis on applications in epilepsy.
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Affiliation(s)
- A Salek-Haddadi
- Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, Queen Square, WC1N 3BG, London, UK.
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25
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Tenney JR, Duong TQ, King JA, Ludwig R, Ferris CF. Corticothalamic modulation during absence seizures in rats: a functional MRI assessment. Epilepsia 2003; 44:1133-40. [PMID: 12919383 PMCID: PMC2962948 DOI: 10.1046/j.1528-1157.2003.61002.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Functional magnetic resonance imaging (fMRI) was used to identify areas of brain activation during absence seizures in an awake animal model. METHODS Blood-oxygenation-level-dependent (BOLD) fMRI in the brain was measured by using T2*-weighted echo planar imaging at 4.7 Tesla. BOLD imaging was performed before, during, and after absence seizure induction by using gamma-butyrolactone (GBL; 200 mg/kg, intraperitoneal). RESULTS The corticothalamic circuitry, critical for spike-wave discharge (SWD) formation in absence seizure, showed robust BOLD signal changes after GBL administration, consistent with EEG recordings in the same animals. Predominantly positive BOLD changes occurred in the thalamus. Sensory and parietal cortices showed mixed positive and negative BOLD changes, whereas temporal and motor cortices showed only negative BOLD changes. CONCLUSIONS With the BOLD fMRI technique, we demonstrated signal changes in brain areas that have been shown, with electrophysiology experiments, to be important for generating and maintaining the SWDs that characterize absence seizures. These results corroborate previous findings from lesion and electrophysiological experiments and show the technical feasibility of noninvasively imaging absence seizures in fully conscious rodents.
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Affiliation(s)
- Jeffrey R Tenney
- Center for Comparative Neuroimaging, Department of Psychiatry, University of Massachusetts Medical School Worcester, Massachusetts 01655, USA.
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26
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Hilton EJR, Hosking SL, Betts T. Epilepsy patients treated with antiepileptic drug therapy exhibit compromised ocular perfusion characteristics. Epilepsia 2002; 43:1346-50. [PMID: 12423384 DOI: 10.1046/j.1528-1157.2002.44901.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Reduced cerebral blood flow and decreased cerebral glucose metabolism have been identified in patients with epilepsy treated with antiepileptic drug (AED) therapy. The purpose of this study was to determine whether ocular haemodynamics are similarly reduced in patients with epilepsy treated with AEDs. METHODS Scanning laser Doppler flowmetry was used to measure retinal capillary microvascular flow, volume, and velocity in the temporal neuroretinal rim of 14 patients diagnosed with epilepsy (mean age, 42.0 +/- 0.9 years). These values were compared with those of an age- and gender-matched normal subject group (n = 14; mean age, 41.7 +/- 0.3 years). Student's unpaired two-tailed t tests were used to compare ocular blood-flow parameters between the epilepsy and normal subject groups (p < 0.05; Bonferroni corrected). RESULTS A significant reduction in retinal blood volume (p = 0.001), flow (p = 0.003), and velocity (p = 0.001) was observed in the epilepsy group (13.52 +/- 3.75 AU, 219.14 +/- 76.61 AU, and 0.77 +/- 0.269 AU, respectively) compared with the normal subject group (19.02 +/- 5.11 AU, 344.03 +/- 93.03 AU, and 1.17 +/- 0.301 AU, respectively). Overall, the percentage mean difference between the epilepsy and normal groups was 36.31% for flow, 28.92% for volume, and 34.19% for velocity. CONCLUSIONS Patients with epilepsy exhibit reduced neuroretinal capillary blood flow, volume, and velocity compared with normal subjects. A reduction in ocular perfusion may have implications for visual function in people with epilepsy.
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Affiliation(s)
- Emma J Roff Hilton
- Neurosciences Research Institute, Aston University, and University Of Birmingham Seizure Clinic, Queen Elizabeth Psychiatric Hospital, Birmingham, England.
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27
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Bonmassar G, Hadjikhani N, Ives JR, Hinton D, Belliveau JW. Influence of EEG electrodes on the BOLD fMRI signal. Hum Brain Mapp 2001; 14:108-15. [PMID: 11500994 PMCID: PMC6871948 DOI: 10.1002/hbm.1045] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Measurement of the EEG during fMRI scanning can give rise to image distortions due to magnetic susceptibility, eddy currents or chemical shift artifacts caused by certain types of EEG electrodes, cream, leads, or amplifiers. Two different creams were tested using MRS and T2* measurements, and we found that the one with higher water content was superior. This study introduces an index that quantifies the influence of EEG equipment on the BOLD fMRI signal. This index can also be used more generally to measure the changes in the fMRI signal due to the presence of any type of device inside (or outside) of the field of view (e.g., with fMRI and diffuse optical tomography, infrared imaging, transcranial magnetic stimulation, ultrasound imaging, etc.). Quantitative noise measurements are hampered by the normal variability of functional activation within the same subject and by the different slice profiles obtained when inserting a subject multiple times inside a MR imaging system. Our measurements account for these problems by using a matched filtering of cortical surface maps of functional activations. The results demonstrate that the BOLD signal is not influenced by the presence of EEG electrodes when using a properly constructed MRI compatible recording cap.
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Affiliation(s)
- G Bonmassar
- A. Martinos Center, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA.
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28
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Krakow K, Baxendale SA, Maguire EA, Krishnamoorthy ES, Lemieux L, Scott CA, Smith SJ. Fixation-off sensitivity as a model of continuous epileptiform discharges: electroencephalographic, neuropsychological and functional MRI findings. Epilepsy Res 2000; 42:1-6. [PMID: 10996501 DOI: 10.1016/s0920-1211(00)00152-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
A case of fixation-off sensitivity (FOS) in an asymptomatic adult is presented and studied as a model for continuous epileptiform discharges. Video-electroencephalographic (EEG) revealed continuous bilateral occipital spike wave discharges during elimination of central vision, which were shown to be associated with transitory cognitive impairment demonstrated by neuropsychological testing. Functional MRI showed activation of parieto-occipital and frontal brain areas during the fixation-off discharges. This localization was confirmed with 64-channel EEG source analysis. The applied methods provided additional information on the pathophysiology of epileptiform discharges.
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Affiliation(s)
- K Krakow
- Epilepsy Research Group, Department of Clinical Neurology, Institute of Neurology, University College London, London, UK.
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29
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Chiappa KH, Hill RA, Huang-Hellinger F, Jenkins BG. Photosensitive epilepsy studied by functional magnetic resonance imaging and magnetic resonance spectroscopy. Epilepsia 1999; 40 Suppl 4:3-7. [PMID: 10487166 DOI: 10.1111/j.1528-1157.1999.tb00899.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE To study metabolic and hemodynamic correlates of photic stimulation-triggered discharges. METHODS Simultaneous EEG, functional MRI (tMRI) and magnetic resonance spectroscopy (MRS) were performed in nine patients with photosensitive epilepsy and in 12 normal subjects. RESULTS Prominent visual cortex activation was seen in all normal subjects and patients, and no tMRI-registered hemodynamic abnormalities were correlated with the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four findings not seen in the normal subjects: (a) slightly, but significantly, elevated lactate levels in the occipital cortex in the resting state; (b) an increased area of visual cortical activation with photic stimulation; (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal, there were noncontiguous areas of signal attenuation most prominent in perirolandic regions; and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus. CONCLUSIONS These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients.
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Affiliation(s)
- K H Chiappa
- Neurology Department, Massachuetts General Hospital, Boston 02214, USA.
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