Higher-order spectral analysis of burst patterns in EEG

Burst suppression patterns in electroencephalograms (EEG's) have been obser ved in a variety of situations including recovery of a subject from a traum atic brain injury. They are associated with grave prognostic outcomes in ne onates, We study power spectral parameters and bispectral parameters of the EEG at baseline, during early recovery from an asphyxic arrest (EEG burst patterns) and during late recovery after EEG evolves into a more continuous activity, The bicoherence indexes, which indicate the degree of phase coup ling between two frequency components of a signal, are significantly higher within the delta-theta band of the EEG bursts than in the baseline of late recovery waveforms, The bispectral parameters show a more detectable trend than the power spectral parameters. In the second part of the study, we lo oked into the possibility of higher (>2) -order nonlinearities in the EEG b ursts using the diagonal slices of the polyspectrum. The diagonal elements of the polyspectrum reveal the presence of self-frequency and self-phase co upling of orders higher than two in majority of the EEG bursts studied. The bicoherence indexes and the diagonal elements of the polyspectrum strongly indicate the presence of nonlinearities of order two and in many cases hig her, in the EEG generator during episodes of bursting. This indication of n onlinearity in EEG signals provides a novel quantitative measure of brain's response to injury.