title: Temporal order of nonlinear dynamics in human brain.
abstract: In previous spectral analysis investigations, we demonstrated that the spontaneous activity of the alpha EEG is not stationary but rather shows cyclic alterations with a circa 1-min periodicity. Following the conclusion that a power increase in the alpha band implies a neuronal synchronization, and vice versa, an associated decrease of the EEG complexity was postulated. Accordingly, a rhythmic variation, i.e., a temporal order of the nonlinear dynamics with similar period length, was expected. Bipolar 4-min EEG recordings were obtained from 20 awake subjects (mean age: 23.5+/-2.5 years) with eyes closed for the EEG leads C3, C4, Oz, and Fz according to the 10-20 system. For the automatic evaluation of spontaneous alterations of complexity, a sliding computation of the so-called correlation dimension, using an analysis window length of 20 s continuously shifted by 1 s, was performed. The time series of complexity exhibited an oscillatory behavior with a mean period length of 58.7 s; the Friedman test statistic revealed no significant topological differences. For the rejection of the null hypothesis that the observed periodicity is a random one, two-group t-tests and ANOVA with repeated measures were performed, comparing the corresponding amplitudes and period lengths with those derived from 20 pseudo-random signals (taken from a multivariate Gaussian normal distribution). The mean relative change of EEG complexity was highly significantly increased (P<0.0001) compared to that of random data. Likewise, the difference of mean period lengths was also significant (P<0.01). The results indicate that the coupling strength of the neural network of the brain changes periodically, with a cyclic alteration from a central to a parallel processing mode of information, reflecting state transitions from synchronized, low-complex EEG activity to desynchronized high-complex activity, and vice versa. Various neuronal control mechanisms that may be acting as pacemakers responsible for the temporal order of such transients are discussed. A disturbance of the temporal order may be of pathophysiological significance.
authors.affiliation: GSF-Institut für Medizinische Informatik und Institut für Biomathematik, D-85764, Neuherberg, Germany. tirsch@gsf.de
authors.forename: W S
authors.initials: WS
authors.lastname: Tirsch
authors.forename: Ph
authors.initials: P
authors.lastname: Stude
authors.forename: H
authors.initials: H
authors.lastname: Scherb
authors.forename: M
authors.initials: M
authors.lastname: Keidel
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D003344:Cortical Synchronization; D004569:Electroencephalography / Q000706:statistics & numerical data; D006801:Humans; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D017711:Nonlinear Dynamics; D016011:Normal Distribution; D010507:Periodicity; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors