Abstract
The main objective of this paper is to examine evidence for the concept that epileptic activity should be envisaged in terms of functional connectivity and dynamics of neuronal networks. Basic concepts regarding structure and dynamics of neuronal networks are briefly described. Particular attention is given to approaches that are derived, or related, to the concept of causality, as formulated by Granger. Linear and non-linear methodologies aiming at characterizing the dynamics of neuronal networks applied to EEG/MEG and combined EEG/fMRI signals in epilepsy are critically reviewed. The relevance of functional dynamical analysis of neuronal networks with respect to clinical queries in focal cortical dysplasias, temporal lobe epilepsies, and “generalized” epilepsies is emphasized. In the light of the concepts of epileptic neuronal networks, and recent experimental findings, the dichotomic classification in focal and generalized epilepsy is re-evaluated. It is proposed that so-called “generalized epilepsies,” such as absence seizures, are actually fast spreading epilepsies, the onset of which can be tracked down to particular neuronal networks using appropriate network analysis. Finally new approaches to delineate epileptogenic networks are discussed.
Highlights
EPILEPTIC NEURONAL NETWORKS: BASIC CONCEPTS, STRUCTURE, AND DYNAMICS Seminal descriptions of neuronal networks in which neurons are the elementary units that transmit signals through synaptic contacts were performed by Ramón y Cajal (1894)
A model of how information may flow in cortical networks was proposed by Abeles (1991), Abeles and Gerstein (1998) who introduced the concept of “synfire chains” meaning synchronous working chains of neurons in a network, i.e., sets of interconnected neurons that participate in common tasks
Considering that the main objective of this paper is to examine evidence for the concept that epileptic activity should be envisaged in terms of functional connectivity and dynamics of neuronal networks, we emphasize here approaches that are derived, or related to the concept of causality, as formulated by Granger (1998) in econometrics
Summary
EPILEPTIC NEURONAL NETWORKS: BASIC CONCEPTS, STRUCTURE, AND DYNAMICS Seminal descriptions of neuronal networks in which neurons are the elementary units that transmit signals through synaptic contacts were performed by Ramón y Cajal (1894). A model of how information may flow in cortical networks was proposed by Abeles (1991), Abeles and Gerstein (1998) who introduced the concept of “synfire chains” meaning synchronous working chains of neurons in a network, i.e., sets of interconnected neurons that participate in common tasks He elaborated this concept further in what he called Corticonics where insights from anatomical and physiological studies are combined with mathematical and computer modeling to obtain quantitative descriptions of cortical functions. Whereas the historical approach to understand higher level operating principles in the brain was to consider it subdivided into anatomical regions with local functional properties, the current approach, inspired by the theoretical analysis of complex networks, as described above, is to emphasize networks interactions and connectivity at short and long range These theoretical considerations provide a convenient approach to better understand the pathophysiology of epilepsies. A fundamental characteristic of these neuronal networks is that their dynamics are essentially non-linear given the non-linear transfer properties of neuronal elements
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