Alzheimer’s disease (AD) is the most common neurodegenerative disorder characterized by cognitive and intellectual deficits andbehavior disturbance. The electroencephalogram (EEG) has been used as a tool for diagnosing AD for several decades. The hallmark of EEGabnormalities in AD patients is a shift of the power spectrum to lower frequencies and a decrease in coherence of fast rhythms. Theseabnormalities are thought to be associated with functional disconnections among cortical areas resulting from death of cortical neurons,axonal pathology, cholinergic deficits, etc. This article reviews main findings of EEG abnormalities in AD patients obtained fromconventional spectral analysis and nonlinear dynamical methods. In particular, nonlinear alterations in the EEG of AD patients, i.e. adecreased complexity of EEG patterns and reduced information transmission among cortical areas, and their clinical implications arediscussed. For future studies, improvement of the accuracy of differential diagnosis and early detection of AD based on multimodalapproaches, longitudinal studies on nonlinear dynamics of the EEG, drug effects on the EEG dynamics, and linear and nonlinear functionalconnectivity among cortical regions in AD are proposed to be investigated. EEG abnormalities of AD patients are characterized by slowedmean frequency, less complex activity, and reduced coherences among cortical regions. These abnormalities suggest that the EEG has utilityas a valuable tool for differential and early diagnosis of AD. 

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