title: Time-variant investigation of quadratic phase couplings caused by amplitude modulation in electroencephalic burst-suppression patterns.
abstract: OBJECTIVE
  Several studies suggest that parameters derived from bispectral analysis of the EEG can be used to characterize specific cortical activation states represented by non linear interaction between brain electrical oscillations. For example, it was shown that so-called bispectral indices can be used to assess the depth of sedation. The methods applied so far are based on interval-related procedures of bispectral analysis. Consequently, the use of the resulting parameters for on-line monitoring or investigations of signal properties during transition periods, e.g., when entering burst-suppression periods, is restricted. The objective of this paper is to provide the methodological basis for a time-continuous (on-line) investigation of quadratic phase coupling induced by amplitude modulation.
  
  
  METHODS
  To accomplish this aim an algorithm is presented which enables the analysis of the temporal development in the degree of amplitude modulation (DAM), e.g., during the transition to burst-suppression periods in patients with severe neurological diseases.
  
  
  RESULTS
  It was found that these periods are associated with increasing DAM compared with the baseline conditions.
authors.affiliation: Institute of Medical Statistics, Computer Science and Documentation, Medical Faculty of the Friedrich Schiller University, Jena, Germany. arnold@imsid.uni-jena.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Arnold
authors.forename: Herbert
authors.initials: H
authors.lastname: Witte
authors.forename: Christoph
authors.initials: C
authors.lastname: Schelenz
mesh_terms: D000465:Algorithms; D004569:Electroencephalography; D006801:Humans; D009862:Online Systems; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors