• Matthias Arnold, Herbert Witte, and Christoph Schelenz.
• Institute of Medical Statistics, Computer Science and Documentation, Medical Faculty of the Friedrich Schiller University, Jena, Germany. arnold@imsid.uni-jena.de
• J Clin Monit Comput. 2002 Feb 1; 17 (2): 115-23.

ObjectiveSeveral 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.MethodsTo 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.ResultsIt was found that these periods are associated with increasing DAM compared with the baseline conditions.

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