Nonlinear Dynamic in the EEG of Schizophrenic
Patients and its Variation with Mental Tasks.

M. Dressel, B. Ambühl-Braun, R .M. Dünki, P.F. Meier & T. Elbert. pp. 348 - 352 in: ``Chaos in Brain'', K. Lehnertz, J. Arnold, P. Grassberger & C.E. Elger (eds.), World Scientific, Singapore, (2000).


The nonlinear dynamic of the EEG from 15 schizophrenic inpatients and 15 controls was estimated by computing the correlation dimension, the singular value decomposition and two other nonlinear parameters using a multichannel embedding. In addition, the traditional powerspectrum was determined at Cz. We recorded the EEG during four conditions including cognitive and perceptual tasks. The result show a significant reduction of the correlation dimension and the singular value decomposition under a wordfluency task within the control group in relation to other conditions. An activation-effect of the wordfluency task or any other condition is not seen in the schizophrenic patient group. Group differences in relation to the conditions cannot be detected in the powerspectrum. Furthermore, there are no significant correlations between the ratings of the psychopathology or the medication and the nonlinear parameters of the EEG. In a neuropsychological view, the present EEG-study reflects cognitive disturbances of schizophrenic patients that are related to prefrontal sites.