title: Analysis and modeling of time-variant amplitude-frequency couplings of and between oscillations of EEG bursts.
abstract: Low-frequency (0.5-2.5 Hz) and individually defined high-frequency (7-11 or 8-12 Hz; 11-15 or 14-18 Hz) oscillatory components of the electroencephalogram (EEG) burst activity derived from thiopental-induced burst-suppression patterns (BSP) were investigated in seven sedated patients (17-26 years old) with severe head injury. The predominant high-frequency burst oscillations (>7 Hz) were detected for each patient by means of time-variant amplitude spectrum analysis. Thereafter, the instantaneous envelope (IE) and the instantaneous frequency (IF) were computed for these low- and high-frequency bands to quantify amplitude-frequency dependencies (envelope-envelope, envelope-frequency, and frequency-frequency correlations). Time-variant phase-locking, phase synchronization, and quadratic phase couplings are associated with the observed amplitude-frequency characteristics. Additionally, these time-variant analyses were carried out for modeled burst patterns. Coupled Duffing oscillators were adapted to each EEG burst and by means of these models data-based burst simulations were generated. Results are: (1) strong envelope-envelope correlations (IE courses) can be demonstrated; (2) it can be shown that a rise of the IE is associated with an increase of the IF (only for the frequency bands 0.5-2.5 and 7-11 or 8-12 Hz); (3) the rise characteristics of all individually averaged envelope-frequency courses (IE-IF) are strongly correlated; (4) for the 7-11 or 8-12 Hz oscillation these associations are weaker and the variation between the time courses of the patients is higher; (5) for both frequency ranges a quantitative amplitude-frequency dependency can be shown because higher IE peak maxima are accompanied by stronger IF changes; (6) the time range of significant phase-locking within the 7-11 or 8-12 Hz frequency bands and of the strongest quadratic phase couplings (between 0.5-2.5 and 7-11 or 8-12 Hz) is between 0 and 1,000 ms; (7) all phase coupling characteristics of the modeled bursts accord well with the corresponding characteristics of the measured EEG burst data. All amplitude-frequency dependencies and phase locking/coupling properties described here are known from and can be discussed using coupled Duffing oscillators which are characterized by autoresonance properties.
authors.affiliation: Institute of Medical Statistics, Computer Sciences and Documentation, Medical Faculty of the Friedrich Schiller University Jena, 07740, Jena, Germany. Herbert.Witte@mti.uni-jena.de
authors.forename: Herbert
authors.initials: H
authors.lastname: Witte
authors.forename: Peter
authors.initials: P
authors.lastname: Putsche
authors.forename: Claudia
authors.initials: C
authors.lastname: Hemmelmann
authors.forename: Christoph
authors.initials: C
authors.lastname: Schelenz
authors.forename: Lutz
authors.initials: L
authors.lastname: Leistritz
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D006259:Craniocerebral Trauma / Q000473:pathology / Q000503:physiopathology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000378:metabolism; D008297:Male; D008433:Mathematics; D008959:Models, Neurological; D010363:Pattern Recognition, Automated; D010507:Periodicity; D012815:Signal Processing, Computer-Assisted; D013874:Thiopental / Q000378:metabolism; D013997:Time Factors
chemical_list: D006993:Hypnotics and Sedatives; D013874:Thiopental