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  • 1
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract Under selected conditions, nonlinear dynamical systems, which can be described by deterministic models, are able to generate so-called deterministic chaos. In this case the dynamics show a sensitive dependence on initial conditions, which means that different states of a system, being arbitrarily close initially, will become macroscopically separated for sufficiently long times. In this sense, the unpredictability of the EEG might be a basic phenomenon of its chaotic character. Recent investigations of the dimensionality of EEG attractors in phase space have led to the assumption that the EEG can be regarded as a deterministic process which should not be mistaken for simple noise. The calculation of dimensionality estimates the degrees of freedom of a signal. Nevertheless, it is difficult to decide from this kind of analysis whether a process is quasiperiodic or chaotic. Therefore, we performed a new analysis by calculating the first positive Lyapunov exponent L 1 from sleep EEG data. Lyapunov exponents measure the mean exponential expansion or contraction of a flow in phase space. L 1 is zero for periodic as well as quasiperiodic processes, but positive in the case of chaotic processes expressing the sensitive dependence on initial conditions. We calculated L 1 for sleep EEG segments of 15 healthy men corresponding to the sleep stages I, II, III, IV, and REM (according to Rechtschaffen and Kales). Our investigations support the assumption that EEG signals are neither quasiperiodic waves nor a simple noise. Moreover, we found statistically significant differences between the values of L 1 for different sleep stages. All together, this kind of analysis yields a useful extension of the characterization of EEG signals in terms of nonlinear dynamical system theory.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Biological cybernetics 64 (1991), S. 307-313 
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract In order to perform an analysis of nonlinear EEG-dynamics we investigated the EEG of ten male probands during sleep. According to Rechtschaffen and Kales (1968) we scored the sleep-EEG and applied an algorithm, proposed by Grassberger and Proccaccia (1983) to compute the correlation dimension of different sleep stages. The correlation dimension characterizes the dynamics of the EEG signal and estimates the degrees of freedom of the signal under study. We could demonstrate, that the EEG of slow wave sleep stages depicts a dimensionality, which is two units smaller than that of light or REM sleep.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Biological cybernetics 82 (2000), S. 477-483 
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. In recent years evidence has accumulated that ECG signals are of a nonlinear nature. It has been recognized that strictly periodic cardiac rhythms are not accompanied by healthy conditions but, on the contrary, by pathological states. Therefore, the application of methods from nonlinear system theory for the analysis of ECG signals has gained increasing interest. Crucial for the application of nonlinear methods is the reconstruction (embedding) of the time series in a phase space with appropriate dimension. In this study continuous ECG signals of 12 healthy subjects recorded during different sleep stages were analysed. Proper embedding dimension was determined by application of two techniques – the false nearest neighbours method and the saturation of the correlation dimension. Results for the ECG signals were compared with findings for simulated data (quasiperiodic dynamics, Lorenz data, white noise) and for phase randomized surrogates. Findings obtained with the two approaches suggest that embedding dimensions from 6 to 8 may be regarded as suitable for the topologically proper reconstruction of ECG signals.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Biological cybernetics 82 (2000), S. 485-491 
    ISSN: 1432-0770
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Informatik , Physik
    Notizen: Abstract. The hypothesis that cardiac rhythms are associated with chaotic dynamics implicating a healthy flexibility has motivated the investigation of continuous ECG with methods of nonlinear system theory. Sleep is known to be associated with modulations of the sympathetic and parasympathetic control of cardiac dynamics. Thus, the differentiation of ECG signals recorded during different sleep stages can serve to determine the usefulness of nonlinear measures in discriminating ECG states in general. For this purpose the following six nonlinear measures were implemented: correlation dimension D2, Lyapunov exponent L1. Kolmogorov entropy K2, as well as three measures derived from the analysis of unstable periodic orbits. Results of this study show that continuous ECG signals can be differentiated from linear stochastic surrogates by each of the nonlinear measures. The most significant finding with respect to the sleep-related differentiation of ECG signals is an increase in dominant chaoticity assessed by L1 and a reduction in the degrees of freedom estimated by D2 during REM sleep compared to slow wave sleep. Our findings suggest that the increase in dominant chaoticity during REM sleep with regard to time-continuous nonlinear analysis is comparable to an increased heart rate variability. The reduction in the correlation dimension may be interpreted as an expression of the withdrawal of respiratory influences during REM sleep.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    European archives of psychiatry and clinical neuroscience 242 (1993), S. 191-196 
    ISSN: 1433-8491
    Schlagwort(e): Sleep EEG ; Deterministic Chaos ; Dimensionality ; Schizophrenia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Deterministic chaos could be regarded as a healthy flexibility of the human brain necessary for correct neuronal operations. Several investigations have demonstrated that in healthy subjects the dimensionality of REM sleep is much higher than that of slow wave sleep (SWS). We investigated the sleep-EEG of schizophrenic patients with methods from nonlinear system theory in order to estimate the dynamic properties of CNS. We hypothesized that schizophrenics would reveal alterations of their dynamic EEG features indicating impaired information processing. In 11 schizophrenic patients, the EEG's dimensionality during sleep stages II and REM was reduced. We suggest that such lower dimensional chaotic processes might be associated with an overloading of neuronal networks during sleep and therefore the psychopathology of schizophrenics might be due to impaired complexity of their EEG's dynamics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    European archives of psychiatry and clinical neuroscience 245 (1995), S. 27-35 
    ISSN: 1433-8491
    Schlagwort(e): Sleep EEG ; Lyapunov exponent ; Deterministic chaos ; Nonlinear dynamics ; Depression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Conventional sleep analysis according to Rechtschaffen and Kales (1968) has provided meaningful contributions to the understanding of disturbed sleep architecture in depression. However, there is no characteristic alteration of the sleep cycle, which could serve as a highly specific feature for depressive illness. Therefore, we started to investigate nonlinear properties of sleep electroencephalographic (EEG) data in order to elucidate functional alterations other than those obtained from classical sleep analysis. The application of methods from nonlinear dynamical system theory to EEG data has led to the assumption that the EEG can be treated as a deterministic chaotic process. Chaotic systems are characterized by a so-called sensitive dependence on initial conditions. This property can be quantified by calculating the system's Lyapunov exponents, which measure the exponential separation of nearby initial states in phase space. For 15 depressive inpatients (major depressive episodes according to DSM-III-R criteria) and 13 healthy controls, matched in gender, age, and education, we computed the principal Lyapunov exponents L1 of EEG segments corresponding to sleep stages I, II, III, IV, and rapid eye movement (REM), according to Rechtschaffen and Kales, for the lead positions CZ and PZ. We found statistically significant decreased values of L1 during sleep stage IV in depressives compared with a healthy control group.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1432-2072
    Schlagwort(e): Key words Microstructure ; Sleep EEG ; Spectral power analysis ; Paroxetine ; Healthy subjects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Paroxetine is a selective and potent serotonin reuptake inhibitor and its efficacy for the treatment of depression has been proven. Under acute and subchronical treatment regimens, disturbances of the regular sleep pattern are a reported side effect of the drug. The present study was therefore performed to investigate the impact of subchronic treatment with the selective serotonin reuptake inhibitor paroxetine on the microstructure of the sleep EEG. The study especially addressed the question of subchronic effects of paroxetine medication (30 mg/day) in eight healthy male volunteers in a double blind, placebo-controlled crossover design. Conventional sleep EEG parameters and a spectral power analysis for different sleep stages after 4 weeks of treatment were computed. Additionally, the correlation of certain EEG rhythms across the night was calculated in order to detect subtle dynamical EEG alterations, not necessarily obvious when regarding conventional EEG analysis. Although we could not detect any alterations of the spectral power values in certain frequency bands either during NREM nor during REM sleep following subchronic paroxetine medication, the dynamical EEG attributes across the night revealed a significant enhancement of the correlation between certain EEG rhythms mainly during NREM sleep.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1433-0407
    Schlagwort(e): Schlüsselwörter Akupunktur ; Depression ; Mianserin ; Placebokontrolliert ; Key words Acupuncture ; Depression ; Mianserine ; Placebo-controlled study
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary In order to examine the efficacy of whole body acupuncture additionally applied to drug treatment in depression, a single-blind placebo-controlled study with 70 inpatients administered to three different treatment groups has been carried out. All patients were pharmacologically treated with the tetracyclic antidepressant mianserin. The verum group (n=22) received acupuncture at specific points considered to be effective in the treatment of depression. The placebo group (n=24) was treated with acupuncture at non-specific locations and the control group (n=24) received only pharmacological treatment. Acupuncture was applied three times a week over a period of four weeks. Psychopathology was rated by judges blind to verum/placebo conditions twice a week over eight weeks with the CGI, GAS, BRMS and BfS rating scales. Additionally applied acupuncture improved the course of depression more than pharmacological treatment with mianserin did by itself. However, we could not detect any differences between placebo and verum acupuncture.
    Notizen: Zusammenfassung Um die Wirksamkeit einer begleitenden Ganzkörperakupunktur bei Patienten mit einer Depression zu untersuchen, wurden 70 stationäre Patienten in eine placebokontrollierte Studie eingeschlossen und randomisiert auf 3 Behandlungsgruppen aufgeteilt. Während alle 3 Gruppen pharmakologisch mit dem tetrazyklischen Antidepressivum Mianserin behandelt wurden, erhielt die Verumakupunkturgruppe (n=22) zusätzlich eine Akupunktur an spezifischen Punkten, die als wirksam in der Behandlung einer Depression angesehen werden. Die Placeboakupunkturgruppe (n=24) wurde mit einer Akupunktur an nicht spezifischen Punkten behandelt, und die Kontrollgruppe (n=24) wurde nur mit Mianserin behandelt. Die Akupunktursitzungen fanden dreimal pro Woche über einen Zeitraum von vier aufeinanderfolgenden Wochen statt. Die psychopathologische Symptomatik wurde zweimal pro Woche über einen Zeitraum von acht aufeinanderfolgenden Wochen mittels der Instrumente CGI, GAS, BRMS und BfS beurteilt. Die Besserung des psychopathologischen Befundes von Patienten, die akupunktiert wurden (Verum- und Placeboakupunktur), war signifikant höher als bei Patienten, die mit Mianserin alleine behandelt wurden. Es ergab sich jedoch kein Unterschied zwischen den beiden Akupunkturgruppen.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 19 (1998), S. 199-202 
    ISSN: 0197-8462
    Schlagwort(e): cellular phone ; sleep EEG ; REM sleep ; spectral power density ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Physik
    Notizen: To investigate the influence of radiofrequency electromagnetic fields (EMFs) of cellular phone GSM signals on human sleep electroencephalographic (EEG) pattern, all-night polysomnographies of 24 healthy male subjects were recorded, both with and without exposure to a circular polarized EMF (900 MHz, pulsed with a frequency of 217 Hz, pulse width 577 μs, power flux density 0.2 W/m2. Suppression of rapid eye movement (REM) sleep as well as a sleep-inducing effect under field exposure did not reach statistical significance, so that previous results indicating alterations of these sleep parameters could not be replicated. Spectral power analysis also did not reveal any alterations of the EEG rhythms during EMF exposure. The failure to confirm our previous results might be due to dose-dependent effects of the EMF on the human sleep profile. Bioelectromagnetics 19:199-202, 1998. © 1998 Wiley-Liss, Inc.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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