Elsevier

Neural Networks

Volume 21, Issue 8, October 2008, Pages 1105-1111
Neural Networks

2008 Special Issue
Neuronal population oscillations of rat hippocampus during epileptic seizures

https://doi.org/10.1016/j.neunet.2008.06.002Get rights and content

Abstract

Neuronal population oscillations in the hippocampus have an important effect in the information processing in the brain and the generation of epileptic seizures. In this paper, we investigate the neuronal population oscillations in the hippocampus of epileptic rats in vivo using an empirical mode decomposition (EMD) method. A neuronal population oscillation can be decomposed into several relaxation oscillations, which possess a recovery and release phase, with the different frequencies that ranges from 0 to 600 Hz. The natures of relaxation oscillations at the pre-ictal, seizure onset and ictal states are distinctly different. The analysis of relaxation oscillations show that the gamma wave is a lead relaxation oscillation at the pre-ictal stage, then it moves to beta oscillation or theta oscillation while the ictal stage starts; the fast relaxation oscillations are associated with the slow relaxation oscillations in the CA1 or CA3, in particular, the fast relaxation oscillations are associated on the recovery phase of the slow relaxation oscillations during the pre-ictal interval, however move to the release phase of the slow relaxation oscillations during the ictal interval. Comparison of the relaxation oscillations in CA1 and CA3 shows that the neurons in the CA1 are more active during the epileptic seizures than during the pre-ictal stage. These findings demonstrate that this method is very helpful to decompose neuronal population for understanding the underlying mechanism of epileptic seizures.

Section snippets

Hippocampal neuronal populations

In this study, the rat tetanus toxin model of focal epilepsy is applied to study the neuronal oscillations in CA1/CA3 of rat hippocampus. Recordings were made during previous studies of this model (Finnerty and Jefferys, 2000, Finnerty and Jefferys, 2002). Methods were described in the previous reports, but briefly, male Sprague-Dawley rats (280–400 g) were anaesthetised with halothane. Bipolar recording electrodes (twisted Teflon-coated stainless steel wire with the tips separated 250–350 μm

EMD of neuronal populations

In this study, we examine the neuronal populations of rat hippocampal areas CA1 and CA3. The EEG recording (Left CA3) in Fig. 1 describes a typical trace from pre-ictal towards ictal state. To identify the dynamical change of neuronal oscillations at the pre-ictal, seizure onset and ictal state, I-II-III segments are extracted for further analysis. The EMD of three segments are plotted in Fig. 1B. It can be seen that a neuronal population oscillation in the hippocampus is composed of IMFs that

Discussion

In this study, the tetanus toxin model of epilepsy is applied on the behaving rats. EMD is used to decompose the neuronal population oscillations from right and left CA1 and CA3. By the observations of 9 seizures from 6 rats with this method, some findings are below: (i) A neuronal population oscillation is composed of several relaxation oscillations. The frequency distribution of neuronal oscillations shows that the difference of dynamic activity between the pre-ictal and ictal stage is

Acknowledgements

This work was partially supported by National Natural Science Foundation of China (60575012), Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP, 20060216003) and Cercia, The University of Birmingham, UK.

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