Brain Advance Access originally published online on November 1, 2006
Brain 2007 130(1):65-77; doi:10.1093/brain/awl304
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Assessing seizure dynamics by analysing the correlation structure of multichannel intracranial EEG
1 Klinik für Epileptologie Bonn, Germany 2 Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn Bonn, Germany
Correspondence to: Kaspar Schindler, Klinik für Epileptologie, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany E-mail: kschindler{at}smile.ch
Epileptic seizures are commonly characterized as ‘hypersynchronous states’. This habit is doubly misleading, because seizures are not necessarily synchronous and are not unchanging ‘states’ but dynamic processes. Here the temporal evolution of the correlation structure in the course of 100 focal onset seizures of 60 patients recorded by intracranial multichannel EEG was assessed. To this end a multivariate method was applied that at its core consists of computing the eigenvalue spectrum of the zero-lag correlation matrix of a short sliding window. Our results show that there are clearly observable and statistically significant changes of the correlation structure of focal onset seizures. Specifically, these changes indicate that the zero-lag correlation of multi-channel EEG either remains approximately unchanged or—especially in the case of secondary generalization—decreases during the first half of the seizures. Then correlation gradually increases again before the seizures terminate. This development was qualitatively independent of the anatomical location of the seizure onset zone and therefore seems to be a generic property of focal onset seizures. We suggest that the decorrelation of EEG activity is due to the different propagation times of locally synchronous ictal discharges from the seizure onset zone to other brain areas. Furthermore we speculate that the increase of correlation during the second half of the seizures may be causally related to seizure termination.
Key Words: correlation structure; eigenvalue spectrum; intracranial EEG; multivariate time series analysis; seizure termination
Received May 17, 2006. Revised August 10, 2006. Accepted September 29, 2006.