Bicoherence of intracranial EEG in sleep, wakefulness and seizures.

摘要: The hypothesis that the intracranial EEG has local structure and short-term non-stationarity is tested with a little-studied measure of non-linear phase coupling, bicoherence in human subdural deep temporal lobe probe data from 11 subjects during sleeping, waking seizure states. This cooperativity estimates proportion energy every possible pair frequency components, F1, F2 (from 1 to 50 Hz this study), satisfies definition quadratic coupling (phase component at F3, which F1 + F2, equals F2). Derived bispectrum, segregates non-Gaussian energy, auto-bicoherence uses components one channel; cross-bicoherence channel for another F3. These higher order spectra are used physical systems detection episodes non-linearity transients, pattern recognition robust classification, relatively immune Gaussian low signal noise ratios. Bicoherence found not be fixed character but quite unstable, agreement hypothesis. can different adjacent segments as brief 1.6 s well electrodes close 6.5 mm, even when looks similar. It rise or fall steeply within millimeters. virtually absent many analysis epochs 17s duration. Other show significant diverse form distribution over bifrequency plane. Isolated peaks, periodic peaks rounded mountain ranges either widely scattered confined few parts generally an invisible feature: cannot usually recognize responsible any obvious correlate raw EEG. During stage II/III sleep overall mean than state. seizures patterns average elevation have wide variance. Maximum maximum power spectrum, bicoherence, skewness asymmetry all vary independently each other. Cross-bicoherence often intermediate between two commonly resembles two. Of known factors contribute transient distinct ongoing wave forms more important our sets. moments very sensitive weak coupling; come several kinds waveforms. New methods needed evaluate their respective contributions. Utility descriptor claimed before carefully defined repeatable brain states studied.