Abstracts

Recently, analysis of the spectral phase in nonlinear dynamical systems has attracted much attention in various areas. Phase investigations, such as synchronisation, in the field of EEG analysis provide new information about the underlying dynamical process. We adjusted these techniques to examine the scale invariance and persistence of the phase information in EEG time series from epilepsy patients using the Hurst coefficient.
Up to now we investigated multi-channel EEG time series of 10 patients, with a duration of more than 60 hours. First we used an appropriate band-pass filter to achieve separated time series in the delta (0-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (13-30 Hz) and gamma (30-40 Hz) band. The Hurst coefficient was then estimated from a time series consisting of successive zero crossings of the filtered EEG amplitude.
A characteristic scale attitude of the spectral phase with persistence in every frequency band was found and a representative phase scale performance for the focal in contrast to the non-focal hemisphere could be observed. Moreover, in some patients specific scale characteristics of the phase in the theta band were predominantly confined to the entorhinal cortex as compared to the phase in the gamma band, which were more localized in the hippocampus proper.
Phase scale information from the theta and gamma band can indicate the focal area in temporal lobe epilepsy. Also, the time course of the phase scale can help to gather more insight into the spatio-temporal dynamics of the epileptogenic process.
[Supported by: Deutsche Forschungsgemeinschaft]