Elsevier

Neuroscience

Volume 126, Issue 2, 2004, Pages 467-484
Neuroscience

Dynamics of non-convulsive epileptic phenomena modeled by a bistable neuronal network

https://doi.org/10.1016/j.neuroscience.2004.03.014Get rights and content

Abstract

It is currently believed that the mechanisms underlying spindle oscillations are related to those that generate spike and wave (SW) discharges. The mechanisms of transition between these two types of activity, however, are not well understood. In order to provide more insight into the dynamics of the neuronal networks leading to seizure generation in a rat experimental model of absence epilepsy we developed a computational model of thalamo-cortical circuits based on relevant (patho)physiological data. The model is constructed at the macroscopic level since this approach allows to investigate dynamical properties of the system and the role played by different mechanisms in the process of seizure generation, both at short and long time scales. The main results are the following: (i) SW discharges represent dynamical bifurcations that occur in a bistable neuronal network; (ii) the durations of paroxysmal and normal epochs have exponential distributions, indicating that transitions between these two stable states occur randomly over time with constant probabilities; (iii) the probabilistic nature of the onset of paroxysmal activity implies that it is not possible to predict its occurrence; (iv) the bistable nature of the dynamical system allows that an ictal state may be aborted by a single counter-stimulus.

Section snippets

Model's structure

The present model is an extended version of the lumped model initially proposed by Lopes da Silva et al. (1974). The latter consisted of a single module, i.e. a cluster of neurons containing two interacting populations. Excitatory cells of main population projected to the interneurons (IN) while the latter fed back on the main cells, inhibiting them with fast GABAA receptor-mediated inhibitory postsynaptic potentials (IPSPs). Each population was described by the time courses of postsynaptic

Different types of model behavior

The model may exhibit two qualitatively different types of behavior, such as seen in the experimental animals (WAG/Rij and GAERS). The output signal may display a waxing and waning “spindle-like” oscillation having a spectrum with a peak at approximately 11 Hz or a high amplitude “seizure-like” oscillation at a frequency around 9 Hz. We refer to the former behavior as “normal on-going” activity while to the latter as paroxysmal activity.

For the reference set of parameters, the model is in a

Basic properties of the model

We constructed a model of interconnected thalamic and cortical populations with parameters directly related to synaptic and cellular properties in order to investigate the mechanisms of generation of synchronized oscillations in a thalamo-cortical neuronal network. We used animal data obtained in rat genetic models of absence epilepsy (WAG/Rij and GAERS) as the basic experimental data to be modeled. The simulation studies of the dynamical behavior of the model and of its sensitivity to a number

Acknowledgements

Piotr Suffczynski was partly sponsored by grant 8 T11E 003 17 from Polish Committee for Scientific Research and by Lopes da Silva Fellowship from the Christelijke Vereniging voor de Verpleging van Lijders aan Epilepsie (Christian Society for the Management of Patients with Epilepsy), Heemstede. We thank anonymous reviewers whose comments were valuable for this paper.

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