Detection of non-linearity in the EEG of schizophrenic patients

Objective: The aim of this study is to detect non-linearity in the EEG of s chizophrenia with a modified method of surrogate data. We also want to iden tify if dimension complexity (correlation dimension using spatial embedding ) could be used as a discriminating statistic to demonstrate non-linearity in the EEG. The difference between the attractor dimension of healthy subje cts and schizophrenic subjects is expected to be interpreted as reflecting some mechanisms underlying brain wave by views of non-linear dynamics analy sis may reflect mechanistic differences. Methods: EEGs were recorded with 14 electrodes in 18 healthy male subjects (average age: 26.3; range: 20-35) and 18 male schizophrenic patients (avera ge age: 30.6; range: 24-40) during a resting eye-closed state. Neither of t wo groups was taking medicines. All artificial epochs in the EEG records we re rejected by an experienced doctor's visual inspection. Results: Testing non-linearity with modified surrogate data, we showed that correlation dimension of EEG data of schizophrenia does refuse the null hy pothesis that the data were resulted from a linear dynamic system, a decrea se of dimension complexity was found in the EEG of schizophrenia compared w ith controls. We interpreted it as the result of the psychopath's dysfuncti on overall brain. The surrogating procedure results in a significant increa se in D,. Conclusions: Non-linearity of the EEG in schizophrenia was proven in our st udy. We think the correlation dimension with spatial embedding as a good di scriminating statistic for testing such non-linearity. Moreover, schizophre nic patients' EEGs were compared with controls and a lower dimension comple xity was found. The results of our study indicate the possibility of using the methods of non-linear time series analysis to identify the EEGs of schi zophrenic patients. (C) 2001 Elsevier Science Ireland Ltd. All rights reser ved.