In this paper, we have combined experimental neurophysiologic recording and statistical analysis to investigate the nonlinear characteristic and the cognitive function of the brain. Spectrum and bispectrum analyses are proposed to extract multiple effective features of electroencephalograph (EEG) signals from Alzheimer's disease (AD) patients and further applied to distinguish AD patients from the normal controls. Spectral analysis based on autoregressive Burg method is first used to quantify the power distribution of EEG series in the frequency domain. Compared to the control group, the relative power spectral density of AD group is significantly higher in the theta frequency band, while lower in the alpha frequency bands. In addition, median frequency of spectrum is decreased, and spectral entropy ratio of these two frequency bands undergoes drastic changes at the P3 electrode in the central-parietal brain region, implying that the electrophysiological behavior in AD brain is much slower and less irregular. In order to explore the nonlinear high order information, bispectral analysis which measures the complexity of phase-coupling is further applied to P3 electrode in the whole frequency band. It is demonstrated that less bispectral peaks appear and the amplitudes of peaks fall, suggesting a decrease of non-Gaussianity and nonlinearity of EEG in ADs. Notably, the application of this method to five brain regions shows higher concentration of the weighted center of bispectrum and lower complexity reflecting phase-coupling by bispectral entropy. Based on spectrum and bispectrum analyses, six efficient features are extracted and then applied to discriminate AD from the normal in the five brain regions. The classification results indicate that all these features could differentiate AD patients from the normal controls with a maximum accuracy of 90.2%. Particularly, different brain regions are sensitive to different features. Moreover, the optimal combination of features obtained by discriminant analysis may improve the classification accuracy. These results demonstrate the great promise for scape EEG spectral and bispectral features as a potential effective method for detection of AD, which may facilitate our understanding of the pathological mechanism of the disease.
This work was supported by Tianjin Municipal Natural Science Foundation under Grant Nos. 12JCZDJC21100 and 13JCZDJC27900, National Natural Science Foundation of China (NSFC) under Grant Nos. 61302002 and 61372010, and Jilin Provincial Natural Science Foundation under Grant No. 20130101170JC.
I. INTRODUCTION II. EXPERIMENT DESIGN AND EEG RECORDING A. Subjects B. EEG recordings and preprocessing III. ANALYSIS METHODS A. Power spectral density analysis 1. Power spectral density 2. Power spectrum density-based features B. Bispectrum analysis 1. Bispectrum 2. Bispectrum-based features C. Statistical analysis IV. RESULTS A. Relative PSD analysis B. Bispectrum analysis C. Classification analysis and discriminant analysis V. DISCUSSION VI. CONCLUSIONS