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Fujiwara H, Kadis DS, Greiner HM, Holland KD, Arya R, Aungaroon G, Fong SL, Arthur TM, Kremer KM, Lin N, Liu W, Mangano DO FT, Skoch J, Horn PS, Tenney JR. Clinical validation of magnetoencephalography network analysis for presurgical epilepsy evaluation. Clin Neurophysiol 2022; 142:199-208. [DOI: 10.1016/j.clinph.2022.07.506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2022] [Revised: 06/29/2022] [Accepted: 07/20/2022] [Indexed: 11/27/2022]
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Millán AP, van Straaten ECW, Stam CJ, Nissen IA, Idema S, Baayen JC, Van Mieghem P, Hillebrand A. Epidemic models characterize seizure propagation and the effects of epilepsy surgery in individualized brain networks based on MEG and invasive EEG recordings. Sci Rep 2022; 12:4086. [PMID: 35260657 PMCID: PMC8904850 DOI: 10.1038/s41598-022-07730-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Accepted: 02/24/2022] [Indexed: 11/08/2022] Open
Abstract
Epilepsy surgery is the treatment of choice for drug-resistant epilepsy patients. However, seizure-freedom is currently achieved in only 2/3 of the patients after surgery. In this study we have developed an individualized computational model based on MEG brain networks to explore seizure propagation and the efficacy of different virtual resections. Eventually, the goal is to obtain individualized models to optimize resection strategy and outcome. We have modelled seizure propagation as an epidemic process using the susceptible-infected (SI) model on individual brain networks derived from presurgical MEG. We included 10 patients who had received epilepsy surgery and for whom the surgery outcome at least one year after surgery was known. The model parameters were tuned in in order to reproduce the patient-specific seizure propagation patterns as recorded with invasive EEG. We defined a personalized search algorithm that combined structural and dynamical information to find resections that maximally decreased seizure propagation for a given resection size. The optimal resection for each patient was defined as the smallest resection leading to at least a 90% reduction in seizure propagation. The individualized model reproduced the basic aspects of seizure propagation for 9 out of 10 patients when using the resection area as the origin of epidemic spreading, and for 10 out of 10 patients with an alternative definition of the seed region. We found that, for 7 patients, the optimal resection was smaller than the resection area, and for 4 patients we also found that a resection smaller than the resection area could lead to a 100% decrease in propagation. Moreover, for two cases these alternative resections included nodes outside the resection area. Epidemic spreading models fitted with patient specific data can capture the fundamental aspects of clinically observed seizure propagation, and can be used to test virtual resections in silico. Combined with optimization algorithms, smaller or alternative resection strategies, that are individually targeted for each patient, can be determined with the ultimate goal to improve surgery outcome. MEG-based networks can provide a good approximation of structural connectivity for computational models of seizure propagation, and facilitate their clinical use.
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Affiliation(s)
- Ana P Millán
- Department of Clinical Neurophysiology and MEG Center, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands.
| | - Elisabeth C W van Straaten
- Department of Clinical Neurophysiology and MEG Center, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
| | - Cornelis J Stam
- Department of Clinical Neurophysiology and MEG Center, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
| | - Ida A Nissen
- Department of Clinical Neurophysiology and MEG Center, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
| | - Sander Idema
- Department of Neurosurgery, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
| | - Johannes C Baayen
- Department of Neurosurgery, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
| | - Piet Van Mieghem
- Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Delft, The Netherlands
| | - Arjan Hillebrand
- Department of Clinical Neurophysiology and MEG Center, Amsterdam Neuroscience, Vrije Universiteit Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands
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Papadelis C, Perry MS. Localizing the Epileptogenic Zone with Novel Biomarkers. Semin Pediatr Neurol 2021; 39:100919. [PMID: 34620466 PMCID: PMC8501232 DOI: 10.1016/j.spen.2021.100919] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 08/09/2021] [Accepted: 08/11/2021] [Indexed: 01/01/2023]
Abstract
Several noninvasive methods, such as high-density EEG or magnetoencephalography, are currently used to delineate the epileptogenic zone (EZ) during the presurgical evaluation of patients with drug resistant epilepsy (DRE). Yet, none of these methods can reliably identify the EZ by their own. In most cases a multimodal approach is needed. Challenging cases often require the implantation of intracranial electrodes, either through stereo-taxic EEG or electro-corticography. Recently, a growing body of literature introduces novel biomarkers of epilepsy that can be used for analyzing both invasive as well as noninvasive electrophysiological data. Some of these biomarkers are able to delineate the EZ with high precision, augment the presurgical evaluation, and predict the surgical outcome of patients with DRE undergoing surgery. However, the use of these epilepsy biomarkers in clinical practice is limited. Here, we summarize and discuss the latest technological advances in the presurgical neurophysiological evaluation of children with DRE with emphasis on electric and magnetic source imaging, high frequency oscillations, and functional connectivity.
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Affiliation(s)
- Christos Papadelis
- Jane and John Justin Neurosciences Center, Cook Children's Health Care System, Fort Worth, TX; School of Medicine, Texas Christian University and University of North Texas Health Science Center, Fort Worth, TX; Department of Bioengineering, University of Texas at Arlington, Arlington, TX; Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA.
| | - M Scott Perry
- Jane and John Justin Neurosciences Center, Cook Children’s Health Care System, Fort Worth, TX, USA
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Human brain connectivity: Clinical applications for clinical neurophysiology. Clin Neurophysiol 2020; 131:1621-1651. [DOI: 10.1016/j.clinph.2020.03.031] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 03/13/2020] [Accepted: 03/17/2020] [Indexed: 12/12/2022]
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Sanz-Garcia A, Rings T, Lehnertz K. Impact of type of intracranial EEG sensors on link strengths of evolving functional brain networks. Physiol Meas 2018; 39:074003. [PMID: 29932428 DOI: 10.1088/1361-6579/aace94] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Objective and Approach: Investigating properties of evolving functional brain networks has become a valuable tool to characterize the complex dynamics of the epileptic brain. Such networks are usually derived from electroencephalograms (EEG) recorded with sensors implanted chronically into deeper structures of the brain and/or placed onto the cortex. It is still unclear, however, whether the use of different sensors for an identification of network nodes affects properties of functional brain networks. We address this question by investigating properties of links of such networks that we characterize by assessing interactions in multi-sensor, multi-day EEG data recorded from 49 epilepsy patients during presurgical evaluation. These data allow us to study the impact of different types of sensors together with the impact of various physiologic and pathophysiologic activities on the properties of links. MAIN RESULTS We observe that different types of sensors differently impact on spatial means and temporal fluctuations of link strengths. Moreover, the impact depends on the relative anatomical location of sensors with respect to location and extent of sources of the prevailing activities. SIGNIFICANCE Type and location of sensors should be considered when constructing networks.
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Affiliation(s)
- Ancor Sanz-Garcia
- Instituto de Investigacion Sanitaria, Hospital Universitario De La Princesa, C/Diego de Leon 62, 28006 Madrid, Spain
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Towards Operational Definition of Postictal Stage: Spectral Entropy as a Marker of Seizure Ending. ENTROPY 2017. [DOI: 10.3390/e19020081] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Sanz-García A, Vega-Zelaya L, Pastor J, Torres CV, Sola RG, Ortega GJ. Network Analysis of Foramen Ovale Electrode Recordings in Drug-resistant Temporal Lobe Epilepsy Patients. J Vis Exp 2016. [PMID: 28060326 PMCID: PMC5226423 DOI: 10.3791/54746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
Abstract
Approximately 30% of epilepsy patients are refractory to antiepileptic drugs. In these cases, surgery is the only alternative to eliminate/control seizures. However, a significant minority of patients continues to exhibit post-operative seizures, even in those cases in which the suspected source of seizures has been correctly localized and resected. The protocol presented here combines a clinical procedure routinely employed during the pre-operative evaluation of temporal lobe epilepsy (TLE) patients with a novel technique for network analysis. The method allows for the evaluation of the temporal evolution of mesial network parameters. The bilateral insertion of foramen ovale electrodes (FOE) into the ambient cistern simultaneously records electrocortical activity at several mesial areas in the temporal lobe. Furthermore, network methodology applied to the recorded time series tracks the temporal evolution of the mesial networks both interictally and during the seizures. In this way, the presented protocol offers a unique way to visualize and quantify measures that considers the relationships between several mesial areas instead of a single area.
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Affiliation(s)
- Ancor Sanz-García
- Neurosurgery & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa;
| | - Lorena Vega-Zelaya
- Clinical Neurophysiology & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa
| | - Jesús Pastor
- Clinical Neurophysiology & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa
| | - Cristina V Torres
- Neurosurgery & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa
| | - Rafael G Sola
- Neurosurgery & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa
| | - Guillermo J Ortega
- Neurosurgery & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa; CONICET
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Nissen IA, Stam CJ, Reijneveld JC, van Straaten IECW, Hendriks EJ, Baayen JC, De Witt Hamer PC, Idema S, Hillebrand A. Identifying the epileptogenic zone in interictal resting-state MEG source-space networks. Epilepsia 2016; 58:137-148. [PMID: 27888520 DOI: 10.1111/epi.13622] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/01/2016] [Indexed: 01/07/2023]
Abstract
OBJECTIVE In one third of patients, seizures remain after epilepsy surgery, meaning that improved preoperative evaluation methods are needed to identify the epileptogenic zone. A potential framework for such a method is network theory, as it can be applied to noninvasive recordings, even in the absence of epileptiform activity. Our aim was to identify the epileptogenic zone on the basis of hub status of local brain areas in interictal magnetoencephalography (MEG) networks. METHODS Preoperative eyes-closed resting-state MEG recordings were retrospectively analyzed in 22 patients with refractory epilepsy, of whom 14 were seizure-free 1 year after surgery. Beamformer-based time series were reconstructed for 90 cortical and subcortical automated anatomic labeling (AAL) regions of interest (ROIs). Broadband functional connectivity was estimated using the phase lag index in artifact-free epochs without interictal epileptiform abnormalities. A minimum spanning tree was generated to represent the network, and the hub status of each ROI was calculated using betweenness centrality, which indicates the centrality of a node in a network. The correspondence of resection cavity to hub values was evaluated on four levels: resection cavity, lobar, hemisphere, and temporal versus extratemporal areas. RESULTS Hubs were localized within the resection cavity in 8 of 14 seizure-free patients and in zero of 8 patients who were not seizure-free (57% sensitivity, 100% specificity, 73% accuracy). Hubs were localized in the lobe of resection in 9 of 14 seizure-free patients and in zero of 8 patients who were not seizure-free (64% sensitivity, 100% specificity, 77% accuracy). For the other two levels, the true negatives are unknown; hence, only sensitivity could be determined: hubs coincided with both the resection hemisphere and the resection location (temporal versus extratemporal) in 11 of 14 seizure-free patients (79% sensitivity). SIGNIFICANCE Identifying hubs noninvasively before surgery is a valuable approach with the potential of indicating the epileptogenic zone in patients without interictal abnormalities.
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Affiliation(s)
- Ida A Nissen
- Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands
| | - Cornelis J Stam
- Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands
| | - Jaap C Reijneveld
- Brain Tumor Center Amsterdam & Department of Neurology, VU University Medical Center, Amsterdam, The Netherlands
| | - Ilse E C W van Straaten
- Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands
| | - Eef J Hendriks
- Department of Radiology & Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands
| | - Johannes C Baayen
- Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands
| | - Philip C De Witt Hamer
- Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands
| | - Sander Idema
- Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands
| | - Arjan Hillebrand
- Department of Clinical Neurophysiology and MEG Center, VU University Medical Center, Amsterdam, The Netherlands
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Etomidate: A Complementary Diagnostic Tool for Pre-Surgical Evaluation in Temporal Lobe Epilepsy. ARCHIVES OF NEUROSCIENCE 2016. [DOI: 10.5812/archneurosci.34915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Vega-Zelaya L, Pastor J, de Sola RG, Ortega GJ. Disrupted Ipsilateral Network Connectivity in Temporal Lobe Epilepsy. PLoS One 2015; 10:e0140859. [PMID: 26489091 PMCID: PMC4619301 DOI: 10.1371/journal.pone.0140859] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Accepted: 10/01/2015] [Indexed: 11/19/2022] Open
Abstract
OBJECTIVE The current practice under which patients with refractory epilepsy are surgically treated is based mainly on the identification of specific cortical areas, mainly the epileptogenic zone, which is believed to be responsible for generation of seizures. A better understanding of the whole epileptic network and its components and properties is required before more effective and less invasive therapies can be developed. The aim of the present study was to partially characterize the evolution of the functional network during the preictal-ictal transition in partial seizures in patients with temporal lobe epilepsy (TLE). METHODS Scalp and foramen ovale (FOE) recordings from twenty-two TLE patients were analyzed under the complex network perspective. The density of links, average path length, average clustering coefficient, and modularity were calculated during the preictal and the ictal stages. Both linear-Pearson correlation-and non-linear-phase synchronization-measures were used as proxies of functional connectivity between the electrode locations areas. The transition from one stage to the other was evaluated in the whole network and in the mesial sub-networks. The results were compared with a voltage-dependent measure, namely, the spectral entropy. RESULTS Changes in the global functional network during the transition from the preictal to the ictal stage show, in the linear case, that in sixteen cases (72.7%) the density of the links increased during the seizure, with a decrease in the average path length in fifteen cases (68.1%). There was also a preictal and ictal imbalance in functional connectivity during both stages (77.2% to 86.3%). The SE dropped during the seizure in 95.4% of the cases, but did not show any tendency towards lateralization. When using the nonlinear measure of functional connectivity, the phase synchronization, similar results were obtained. CONCLUSIONS In TLE patients, the transition to the ictal stage is accompanied by increasing global synchronization and a more ordered spectral content of the signals, indicated by lower spectral entropy. The interictal connectivity imbalance (lower ipsilateral connectivity) is sustained during the seizure, irrespective of any appreciable imbalance in the spectral entropy of the mesial recordings.
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Affiliation(s)
- Lorena Vega-Zelaya
- Clinical Neurophysiology, Hospital Universitario la Princesa, Madrid, Spain
- Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Jesús Pastor
- Clinical Neurophysiology, Hospital Universitario la Princesa, Madrid, Spain
- Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Rafael G. de Sola
- Neurosurgery, Hospital Universitario la Princesa, Madrid, Spain
- Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Guillermo J. Ortega
- Neurosurgery, Hospital Universitario la Princesa, Madrid, Spain
- Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
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Vega-Zelaya L, Pastor J, Tormo I, de Sola RG, Ortega GJ. Assessing the equivalence between etomidate and seizure network dynamics in temporal lobe epilepsy. Clin Neurophysiol 2015; 127:169-178. [PMID: 26070516 DOI: 10.1016/j.clinph.2015.05.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 04/09/2015] [Accepted: 05/06/2015] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Etomidate mimics some typical epileptic neurophysiological features, such as the appearance of spikes and high frequency oscillations, when it is administrated to epileptic patients. However, little is known about its influence on the underlying cortical network. An assessment of comparable cortical dynamics between seizures and etomidate would allow for a more detailed study of the network parameters underlying the ictal stage by using etomidate as a proxy. The objective of the present work is to show that temporal lobe seizures produce network changes comparable to the ones elicited by etomidate administration. METHODS Scalp and foramen ovale electrodes (FOE) recordings from nine temporal lobe epilepsy patients were analyzed under the complex network perspective. The clustering coefficients, average path lengths, density of links, modularity and spectral entropy were calculated during the pre-ictal and ictal stages and post-etomidate administration. Etomidate administration produced no seizure in any of the analyzed cases. RESULTS The density of lines (six of nine patients) and spectral entropy (eight of nine patients) displayed similar behavior to the preictal-ictal transition when etomidate effects altered the epileptic network (FOE+scalp). When considering only the mesial sub-network, changes induced by etomidate perfusion replicated the same type of imbalance observed during the ictal stage in the nine patient's sample and in eight out of nine regarding the preictal stage. Both statistical significance at a level of 1% and size effects, evaluated by using the standardized mean differences, show similar network changes during the preictal-ictal and preictal-etomidate transitions. CONCLUSIONS Etomidate perfusion in patients with temporal lobe epilepsy induces network changes comparable to the changes resulting from seizures. SIGNIFICANCE The finding reported here could improve the study of network dynamics during the ictal phase, not only with electrophysiological methods, but also in other cases, such as functional magnetic resonance imaging.
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Affiliation(s)
- Lorena Vega-Zelaya
- Clinical Neurophysiology, Hospital Universitario de la Princesa, Madrid, Spain; Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Jesús Pastor
- Clinical Neurophysiology, Hospital Universitario de la Princesa, Madrid, Spain; Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Isabel Tormo
- Clinical Neurophysiology, Hospital Universitario de la Princesa, Madrid, Spain
| | - Rafael G de Sola
- Neurosurgery, Hospital Universitario de la Princesa, Madrid, Spain; Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain
| | - Guillermo J Ortega
- Neurosurgery, Hospital Universitario de la Princesa, Madrid, Spain; Instituto de Investigación Sanitaria Hospital Universitario de la Princesa, Madrid, Spain.
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Lehnertz K, Dickten H. Assessing directionality and strength of coupling through symbolic analysis: an application to epilepsy patients. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2015; 373:rsta.2014.0094. [PMID: 25548267 PMCID: PMC4281866 DOI: 10.1098/rsta.2014.0094] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Inferring strength and direction of interactions from electroencephalographic (EEG) recordings is of crucial importance to improve our understanding of dynamical interdependencies underlying various physiological and pathophysiological conditions in the human epileptic brain. We here use approaches from symbolic analysis to investigate--in a time-resolved manner--weighted and directed, short- to long-ranged interactions between various brain regions constituting the epileptic network. Our observations point to complex spatial-temporal interdependencies underlying the epileptic process and their role in the generation of epileptic seizures, despite the massive reduction of the complex information content of multi-day, multi-channel EEG recordings through symbolization. We discuss limitations and potential future improvements of this approach.
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Affiliation(s)
- Klaus Lehnertz
- Department of Epileptology, University of Bonn, Sigmund-Freud-Straße 25, 53105 Bonn, Germany Helmholtz Institute for Radiation and Nuclear Physics, University of Bonn, Nussallee 14-16, 53115 Bonn, Germany Interdisciplinary Center for Complex Systems, University of Bonn, Brühler Straße 7, 53175 Bonn, Germany
| | - Henning Dickten
- Department of Epileptology, University of Bonn, Sigmund-Freud-Straße 25, 53105 Bonn, Germany Helmholtz Institute for Radiation and Nuclear Physics, University of Bonn, Nussallee 14-16, 53115 Bonn, Germany Interdisciplinary Center for Complex Systems, University of Bonn, Brühler Straße 7, 53175 Bonn, Germany
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Porz S, Kiel M, Lehnertz K. Can spurious indications for phase synchronization due to superimposed signals be avoided? CHAOS (WOODBURY, N.Y.) 2014; 24:033112. [PMID: 25273192 DOI: 10.1063/1.4890568] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We investigate the relative merit of phase-based methods-mean phase coherence, unweighted and weighted phase lag index-for estimating the strength of interactions between dynamical systems from empirical time series which are affected by common sources and noise. By numerically analyzing the interaction dynamics of coupled model systems, we compare these methods to each other with respect to their ability to distinguish between different levels of coupling for various simulated experimental situations. We complement our numerical studies by investigating consistency and temporal variations of the strength of interactions within and between brain regions using intracranial electroencephalographic recordings from an epilepsy patient. Our findings indicate that the unweighted and weighted phase lag index are less prone to the influence of common sources but that this advantage may lead to constrictions limiting the applicability of these methods.
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Affiliation(s)
- Stephan Porz
- Department of Epileptology, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany
| | - Matthäus Kiel
- Department of Epileptology, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany
| | - Klaus Lehnertz
- Department of Epileptology, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany
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Centeno M, Carmichael DW. Network Connectivity in Epilepsy: Resting State fMRI and EEG-fMRI Contributions. Front Neurol 2014; 5:93. [PMID: 25071695 PMCID: PMC4081640 DOI: 10.3389/fneur.2014.00093] [Citation(s) in RCA: 117] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Accepted: 05/25/2014] [Indexed: 12/18/2022] Open
Abstract
There is a growing body of evidence pointing toward large-scale networks underlying the core phenomena in epilepsy, from seizure generation to cognitive dysfunction or response to treatment. The investigation of networks in epilepsy has become a key concept to unlock a deeper understanding of the disease. Functional imaging can provide valuable information to characterize network dysfunction; in particular resting state fMRI (RS-fMRI), which is increasingly being applied to study brain networks in a number of diseases. In patients with epilepsy, network connectivity derived from RS-fMRI has found connectivity abnormalities in a number of networks; these include the epileptogenic, cognitive and sensory processing networks. However, in majority of these studies, the effect of epileptic transients in the connectivity of networks has been neglected. EEG–fMRI has frequently shown networks related to epileptic transients that in many cases are concordant with the abnormalities shown in RS studies. This points toward a relevant role of epileptic transients in the network abnormalities detected in RS-fMRI studies. In this review, we summarize the network abnormalities reported by these two techniques side by side, provide evidence of their overlapping findings, and discuss their significance in the context of the methodology of each technique. A number of clinically relevant factors that have been associated with connectivity changes are in turn associated with changes in the frequency of epileptic transients. These factors include different aspects of epilepsy ranging from treatment effects, cognitive processes, or transition between different alertness states (i.e., awake–sleep transition). For RS-fMRI to become a more effective tool to investigate clinically relevant aspects of epilepsy it is necessary to understand connectivity changes associated with epileptic transients, those associated with other clinically relevant factors and the interaction between them, which represents a gap in the current literature. We propose a framework for the investigation of network connectivity in patients with epilepsy that can integrate epileptic processes that occur across different time scales such as epileptic transients and disease duration and the implications of this approach are discussed.
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Affiliation(s)
- Maria Centeno
- Imaging and Biophysics Unit, Institute of Child Health, University College London , London , UK ; Epilepsy Unit, Great Ormond Street Hospital , London , UK
| | - David W Carmichael
- Imaging and Biophysics Unit, Institute of Child Health, University College London , London , UK ; Epilepsy Unit, Great Ormond Street Hospital , London , UK
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Pastor J, Sola RG, Ortega GJ. Influence of paroxysmal activity on background synchronization in epileptic recordings. J Neurosci Methods 2013; 223:69-73. [PMID: 24333290 DOI: 10.1016/j.jneumeth.2013.11.027] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 11/25/2013] [Accepted: 11/27/2013] [Indexed: 11/17/2022]
Abstract
BACKGROUND The presence of spikes and sharp waves in recordings of epileptic patients contaminates background signal synchronization. When estimating functional connectivity between extended cortical areas, the influence of epileptic spikes in specific areas should be considered; however, this step is sometimes overlooked. We present a simple method for quantifying the influence of epileptic activity on background signal synchronization. METHOD Standard synchronization measures were calculated for both pure correlated Gaussian signals and correlated Gaussian signals with different levels of epileptic spikes in order to determine the influence of epileptic activity on synchronization estimates. RESULTS Synchronization from invasive epileptic recordings (e.g., depth electrodes) displays a much higher bias due to epileptic activity than superficial electrodes. Moreover, statistical methods such as mutual information are more affected by spike presence than phase synchronization methods. The influence of spikes is far greater at low values of background synchronization. CONCLUSIONS The information provided by this procedure makes it possible to differentiate true background synchronization from spike synchronization. Thus, our procedure serves as a guide for analyzing synchronization and functional connectivity calculations in epileptic recordings.
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Affiliation(s)
- Jesús Pastor
- Instituto de Investigación Sanitaria Hospital de la Princesa, Madrid, Spain
| | - Rafael G Sola
- Instituto de Investigación Sanitaria Hospital de la Princesa, Madrid, Spain
| | - Guillermo J Ortega
- Instituto de Investigación Sanitaria Hospital de la Princesa, Madrid, Spain.
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Pastor J, Sola RG, Zelaya LV, Garnés O, Ortega G. New network and synchronization approaches in focal epilepsy research and treatment. Health (London) 2013. [DOI: 10.4236/health.2013.56a1001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Extrahippocampal desynchronization in nonlesional temporal lobe epilepsy. EPILEPSY RESEARCH AND TREATMENT 2012; 2012:823683. [PMID: 22957245 PMCID: PMC3420646 DOI: 10.1155/2012/823683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 09/14/2011] [Accepted: 09/25/2011] [Indexed: 11/17/2022]
Abstract
Although temporal lobe epilepsy (TLE) is traditionally associated with both hypersynchronous activity in the form of interictal epileptic discharges and hippocampal sclerosis, recent findings suggest that desynchronization also plays a central role in the dynamics of this pathology. The objective of this work is to show the imbalance existing between mesial activities in patients suffering from mesial TLE, with normal mesial structures. Foramen ovale recordings from six patients with mesial TLE and one with lateral TLE were analyzed through a cluster analysis and synchronization matrices. None of the patients present findings in the MRI presurgical evaluation. Numerical analysis was carried out in three different situations: awake and sleep interictal and also during the preictal stage. High levels of desynchronization ipsilateral to the epileptic side were present in mesial TLE patients. Low levels of desynchronization were present in the lateral TLE patient during the interictal stage and almost zero in the preictal stage. Implications of these findings in relation with seizure spreading are discussed.
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Palmigiano A, Pastor J, García de Sola R, Ortega GJ. Stability of synchronization clusters and seizurability in temporal lobe epilepsy. PLoS One 2012; 7:e41799. [PMID: 22844524 PMCID: PMC3402406 DOI: 10.1371/journal.pone.0041799] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 06/25/2012] [Indexed: 01/03/2023] Open
Abstract
PURPOSE Identification of critical areas in presurgical evaluations of patients with temporal lobe epilepsy is the most important step prior to resection. According to the "epileptic focus model", localization of seizure onset zones is the main task to be accomplished. Nevertheless, a significant minority of epileptic patients continue to experience seizures after surgery (even when the focus is correctly located), an observation that is difficult to explain under this approach. However, if attention is shifted from a specific cortical location toward the network properties themselves, then the epileptic network model does allow us to explain unsuccessful surgical outcomes. METHODS The intraoperative electrocorticography records of 20 patients with temporal lobe epilepsy were analyzed in search of interictal synchronization clusters. Synchronization was analyzed, and the stability of highly synchronized areas was quantified. Surrogate data were constructed and used to statistically validate the results. Our results show the existence of highly localized and stable synchronization areas in both the lateral and the mesial areas of the temporal lobe ipsilateral to the clinical seizures. Synchronization areas seem to play a central role in the capacity of the epileptic network to generate clinical seizures. Resection of stable synchronization areas is associated with elimination of seizures; nonresection of synchronization clusters is associated with the persistence of seizures after surgery. DISCUSSION We suggest that synchronization clusters and their stability play a central role in the epileptic network, favoring seizure onset and propagation. We further speculate that the stability distribution of these synchronization areas would differentiate normal from pathologic cases.
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Affiliation(s)
| | - Jesús Pastor
- Instituto de Investigación Sanitaria Hospital de la Princesa, Madrid, Spain
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