In JoVE (1)

Other Publications (18)

Articles by Guillermo J. Ortega in JoVE

 JoVE Medicine

Network Analysis of Foramen Ovale Electrode Recordings in Drug-resistant Temporal Lobe Epilepsy Patients

1Neurosurgery & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa, 2Clinical Neurophysiology & National Reference Unit for the Treatment of Refractory Epilepsy, Instituto de Investigación Sanitaria Hospital de la Princesa, 3CONICET

JoVE 54746

Other articles by Guillermo J. Ortega on PubMed

Conditioned Spikes: a Simple and Fast Method to Represent Rates and Temporal Patterns in Multielectrode Recordings

Journal of Neuroscience Methods. Feb, 2004  |  Pubmed ID: 14757354

Increasing evidence suggests that the brain utilizes distributed codes that can only be analyzed by simultaneously recording the activity of multiple neurons. This paper introduces a new methodology for studying neural ensemble recordings. The method uses a novel representation to provide complementary information about the stimuli which are contained in the temporal pattern of the spike sequence. By using this procedure, a high correlation of synchronized events with stimuli times is apparent. To quantify the results and to compare the performance of this method against the most traditional raster plot, we have used Fano factor and cross-correlation analysis. Our results suggest that several consecutive spikes from different neurons within an extended time window may encode behaviorally relevant information. We propose that this new representation, in addition to the other approaches currently used (standard raster plots, multivariate statistical methods, neuronal networks, information theory, etc.), can be a useful procedure to describe population spike dynamics.

Synchronization Clusters of Interictal Activity in the Lateral Temporal Cortex of Epileptic Patients: Intraoperative Electrocorticographic Analysis

Epilepsia. Feb, 2008  |  Pubmed ID: 17825075

Drug-resistant temporal lobe epilepsy (TLE) can be treated by tailored surgery guided by electrocorticography (ECoG). Although its value is still controversial, ECoG activity can provide continuous information on intracortical interactions that may be useful to understand the pathophysiology of TLE. The goal of this study is to characterize local interactions in multichannel ECoG recordings of the lateral cortex of TLE patients using three synchronization measures and to link this information with surgical outcome.

Complex Network Analysis of Human ECoG Data

Neuroscience Letters. Dec, 2008  |  Pubmed ID: 18848970

Localization of the epileptogenic zone (EZ) is an important issue in epileptology, even though there is not a unique definition of the epileptic focus. By using complex network analysis of electrocorticographic (ECoG) data we identify three singular areas in the temporal lobe of epileptic patients, the node with highest local synchronization power, the most connected node, and the node with highest interactions load. Connectivity in the data is extracted from the Minimum Spanning Tree (MST) of global correlations. We address the question whether removal of these nodes during the surgery is crucial in the suppression or reduction in the quantity of post-operative seizures. From five ECoG records, local areas with high synchronization power appear to be significantly involved in the development of epileptic seizures. The other two areas seem not to be fundamental in the seizures onset and development. Moreover, the approach proposed shed new light in cortical connectivity patterns in the human temporal lobe. All the analyzed records are during the inter-ictal state.

[Differential Contribution of Preoperatory Studies to Diagnosis in Temporal Lobe Epilepsy Surgery]

Revista De Neurologia. Oct, 2010  |  Pubmed ID: 20859920

It is necessary to know the degree of concordance of preoperative studies in temporal lobe epilepsy (TLE). AIM. To analyze the relative importance of different preoperative tests (vEEG, EEG, SPECT and MRI), the degree of agreement between them, and to develop a Bayesian probability model for diagnosis.

Impaired Mesial Synchronization in Temporal Lobe Epilepsy

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology. Jun, 2011  |  Pubmed ID: 21185775

Temporal lobe epilepsy is commonly associated with synchronous, hyper-synchronous and des-synchronous activity. The aim of the present work is to explore synchronization activity in both mesial areas in temporal lobe epileptic patients during the interictal state.

[Significance of Complex Analysis of Electrical Activity in Temporal Lobe Epilepsy: Foramen Ovale Electrodes Records]

Revista De Neurologia. Jan, 2011  |  Pubmed ID: 21246488

Temporal lobe epilepsy (TLE) is commonly associated with the process of synchronisation during the interictal stage, which show up as 'spikes' on neurophysiological recordings, and also with hypersynchronic activity during clinical seizures. Nevertheless, desynchronisation also seems to play an important role in the epileptogenic process, favouring the onset of seizures.

[Family History of Epilepsy Resistant to Treatment]

Revista De Neurologia. May, 2011  |  Pubmed ID: 21484723

Family aggregation can help determine the risk of epilepsy among relatives. Our aims are to describe the prevalence of family precedents of epilepsy among the diagnosed patients' relatives of the first and second degree, and to look for an association with diverse clinical variables.

[Significance of Complex Analysis of Electrical Activity in Temporal Lobe Epilepsy: Electrocorticography]

Revista De Neurologia. Aug, 2012  |  Pubmed ID: 22829084

Locating and excising epileptogenic zones is the traditional treatment in pharmacoresistant temporal lobe epilepsy. Some patients, however, continue to suffer from attacks even after surgery. Therefore, new hypotheses must be formulated in order to account for the apparent shortcomings of correctly performed surgical procedures.

Stability of Synchronization Clusters and Seizurability in Temporal Lobe Epilepsy

PloS One. 2012  |  Pubmed ID: 22844524

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.

Extrahippocampal Desynchronization in Nonlesional Temporal Lobe Epilepsy

Epilepsy Research and Treatment. 2012  |  Pubmed ID: 22957245

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.

Influence of Paroxysmal Activity on Background Synchronization in Epileptic Recordings

Journal of Neuroscience Methods. Feb, 2014  |  Pubmed ID: 24333290

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.

[Functional Connectivity and Complex Networks in Focal Epilepsy. Pathophysiology and Therapeutic Implications]

Revista De Neurologia. May, 2014  |  Pubmed ID: 24777769

The traditional surgical approach to treat drug-resistant focal epileptic patients is in the resection or disconnection of the epileptic focus. However, a significant minority of patients continue to experience seizures after surgery, which shows the incomplete level of knowledge that currently we have of this pathology.

Plasma Albumin Induces Cytosolic Calcium Oscilations and DNA Synthesis in Human Cultured Astrocytes

BioMed Research International. 2014  |  Pubmed ID: 24967376

So far, a little is known about transition from normal to focal epileptic brain, although disruption in blood-brain barrier and albumin had recently involved. The main objective of this work is to characterize the response of cultured human astrocytes to plasma albumin, including induction of DNA synthesis. Cortical tissue was obtained from 9 patients operated from temporal lobe epilepsy. Astrocytes were cultured for 3-4 weeks and cytosolic calcium concentration ([Ca(2+)]c) was measured. Bovine and human plasma albumin were used. We observed that low albumin concentration decreases [Ca(2+)]c, while higher concentration, induces increase in [Ca(2+)]c. It was shown that increase in [Ca(2+)] c was mediated by inositol 1,4,5-trisphosphate and released from internal stores. Increase in [Ca(2+)]c was reduced to 19% by blocking the transforming growth factor-beta (TGF-βR) receptor. Albumin induces DNA synthesis in a dose-response manner. Finally, induction of DNA synthesis can be partially blocked by heparin and block of TGF-β; however, the combination of both incompletely inhibits DNA synthesis. Therefore, results suggest that mechanisms other than Ca(2+) signals and TGF-β receptor activation might induce DNA synthesis in a lesser degree. These results may be important to further understand the mechanisms involved in the transition from normal to focal epileptic brain.

Inhomogeneous Cortical Synchronization and Partial Epileptic Seizures

Frontiers in Neurology. 2014  |  Pubmed ID: 25309507

Interictal synchronization clusters have recently been described in several publications using diverse techniques, including neurophysiological recordings and fMRI, in patients suffering from epilepsy. However, little is known about the role of these hyper-synchronous areas during seizures. In this work, we report an analysis of synchronization clusters jointly with several network measures during seizure activity; we then discuss our findings in the context of prior literature.

Identification of Redundant and Synergetic Circuits in Triplets of Electrophysiological Data

Journal of Neural Engineering. Dec, 2015  |  Pubmed ID: 26447632

Neural systems are comprised of interacting units, and relevant information regarding their function or malfunction can be inferred by analyzing the statistical dependencies between the activity of each unit. While correlations and mutual information are commonly used to characterize these dependencies, our objective here is to extend interactions to triplets of variables to better detect and characterize dynamic information transfer.

Disrupted Ipsilateral Network Connectivity in Temporal Lobe Epilepsy

PloS One. 2015  |  Pubmed ID: 26489091

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).

Assessing the Equivalence Between Etomidate and Seizure Network Dynamics in Temporal Lobe Epilepsy

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology. Jan, 2016  |  Pubmed ID: 26070516

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.

Corrigendum to "Plasma Albumin Induces Cytosolic Calcium Oscilations and DNA Synthesis in Human Cultured Astrocytes"

BioMed Research International. 2016  |  Pubmed ID: 27529065

[This corrects the article DOI: 10.1155/2014/539140.].

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