[The Empirical Mode Decomposition and Lempel-Ziv Complexity. The New Possibility in Diagnosis of EEG in Schizophrenic Patients?]

Background: Over the last few decades, numerous attempts have been made to identify electroencephalographic (EEG) manifestations of schizophrenia. However, clinical applicability of these studies has not been demonstrated.

Material And Methods: A novel approach to EEG analysis which is based on combination of two methods of time series analysis was presented. Empirical mode decomposition is used to decompose a signal into several independent mode functions (IMF). Then, Lempel-Ziv complexity is used to quantify variability of such modes. We dub this approach EMD-LZC analysis. We carry out EMD-LZC analysis of EEG (performed according to 10-20 standard) of 21 healthy volunteers and 19 schizophrenic patients who were not medicated for at least a week.

Results: We find that variability of the third IMF mode is lower in the patients. The statistically significant differences were observed in 14 channels. Interestingly enough, the Fourier power spectra of both cohorts were not statistically different in any of 19 EEG channels.

Conclusions: Unlike traditional spectral analysis, the combination of empirical mode decomposition and Lempel-Ziv complexity enabled us to identify the properties of EEG that are affected by schizophrenia. The future, more extensive, studies should verify the applicability of the proposed algorithm to diagnostics of schizophrenia. Moreover, we would like to link the observed differences in EEG variability to the pathogenesis of this disease.