Copyright © 2007 Elsevier Inc. All rights reserved.
Short-term changes in bilateral hippocampal coherence precede epileptiform events
Ralph Meiera, b, , 1, , Ute Häusslera, b, c, 1, Ad Aertsena, b, Colin Deransartc, Antoine Depaulisc and Ulrich Egerta, b
aBernstein Center for Computational Neuroscience Freiburg, Hansastrasse 9a, 79104 Freiburg, Germany
bNeurobiology and Biophysics, Faculty of Biology, Albert-Ludwigs-University, Schänzlestrasse 1, 79104 Freiburg, Germany
cU836 Inserm-Université Joseph Fourier-CEA, 2280 Rue de la Piscine, BP 38041 Grenoble Cedex 9, France
Received 16 April 2007; revised 6 June 2007; accepted 20 July 2007. Available online 1 August 2007.
The mesial temporal lobe
epilepsy syndrome (MTLE) is the most common form of focal epilepsies.
MTLE patients usually respond very little to pharmacological therapy
and surgical resection of temporal brain areas is mandatory. Finding
less invasive therapies than resection of the sclerotic hippocampus
requires knowledge of the network structures and dynamics involved in
seizure generation. Investigation of the time interval immediately
preceding seizure onset would help in understanding the initiation
mechanisms of the seizure proper and, thereby, possibly improve
therapeutical options. Here, we employed the in vivo
intrahippocampal kainate model in mice, which is characterized by
unilateral histological changes, resembling hippocampal sclerosis
observed in human MTLE, and recurrent focal seizures. In these
epileptic mice, population spikes occurred during epileptiform events
(EEs) in the ipsilateral, histologically changed hippocampus, but also
concomitantly in the contralateral, intact hippocampus. We studied
synchronization processes between the ipsilateral, sclerotic
hippocampus and the contralateral hippocampus immediately preceding the
onset of EEs. We show that coherence between the two hippocampi
decreased consistently and reliably for all EEs at 8 to 12 s
before their onset at high frequencies (> 100 Hz), without
changes in power in these bands. This early decoupling of the two
hippocampi indicates the time range for cellular and network mechanisms
leading to increased excitability and/or synchronicity in the tissue
and thus ultimately to epileptic seizures.
author. Bernstein Center for Computational Neuroscience Hansastr. 9A,
79104 Freiburg i.Br., Germany. Fax: +49 761 203 9559.1
Both authors contributed equally to this work.