An estimation of the first positive Lyapunov exponent of the EEG in patients with schizophrenia

We studied the complexity of the electroencephalogram (EEG) in schizophreni c patients by estimating the first Lyapunov exponent (L1), which might serv e as an indicator of the specific brain function in schizophrenia. We recor ded the EEG from 25 schizophrenic patients (12 male, 13 female, age = 25.1 +/- 7.0 years) fulfilling DSM-IV criteria and 15 healthy controls (9 male, 6 female; age = 27.8 +/- 4.2 years) at 16 electrodes, different from previo us studies which recorded the EEGs at limited electrodes. We employed a met hod with an optimal embedding dimension to calculate the L1s. For limited n oisy data, this algorithm was strikingly faster and more accurate than prev ious ones. Our results showed that the schizophrenic patients had lower val ues of the L1 at the left inferior frontal and anterior temporal regions co mpared with normal controls. These results for L1 in non-linear analysis ha ve some differences from those for power ratios in linear analysis. These s uggest that the non-linear analysis of the EEGs such as the estimation of t he L1 might be a useful tool in analyzing EEG data to explore the neurodyna mics of the brains of schizophrenic patients. (C) 3000 Elsevier Science Ire land Ltd. All rights reserved.