Quantitative EEG in early Alzheimer's disease patients - power spectrum and complexity features.

The goal of this study was to investigate the EEG signs of early stage Alzheimer's disease (AD) by conventional analyses and by methods quantifying linear and nonlinear EEG-complexity. The EEG was recorded in 12 mild AD patients and in an age-matched healthy control group (24 subjects) in both eyes open and eyes closed conditions. Frequency spectra, Omega-complexity and Synchronization likelihood were calculated on the data. In the patients a significant decrease of the relative alpha and increase of the theta power were found. Remarkably increased Omega-complexity and lower Synchronization likelihood were observed in AD in the 0.5-25 Hz frequency ranges. It is concluded that both spectral- and EEG-complexity changes can be found already in the early stage of AD in a wide frequency range. Application of conventional EEG analysis methods in combination with quantification of EEG-complexity may improve the chances of early diagnosis of AD.

[Quantitative EEG analysis in Alzheimer's disease: spectral, coherence and complexity parameters]. / Kvantitatív EEG Alzheimer-kórban: spektrális-, koherencia- és komplexitás-jellemzok.

In our study we examined the linear and non-linear characteristics of EEG signals derived from patients with Alzheimer's disease (AD) with the future aim of developing a widely available method for monitoring therapy and the progression of the disease or to be used even for the purposes of differential diagnosis. EEG was recorded with eyes closed and eyes open conditions ("resting") in a group of patients with early-stage AD and in healthy control subjects matched by age. In addition to the conventional methods of analysis (frequency spectrum, coherence), the so-called complexity measures developed in recent years (Omega-complexity, synchronised probability) have also been determined. By means of frequency spectrum analysis, we managed to detect the slowdown of EEG in the early stage of dementia, a feature that so far has been associated with the later stages of AD. Coherence was reduced in the majority of frequency bands in the patient group; however, this difference could be observed only in some of the leads. Thus, resting EEG coherence is less suitable for separating various stages than the other methods. Complexity features have shown the most robust changes in Alzheimer's disease in our investigation. Besides the reduction in synchronised probability, significantly higher values of Omega-complexity were obtained in the patient group. This may be associated with the impairment of cortical afferentation (cholinergic and monoaminergic) and with the reduction in the number of neurons and synapses. Our methods have proved to be very sensitive to quantify these changes.

Spectral and complexity features of the EEG changed by visual input in a case of subcortical stroke compared to healthy controls.

OBJECTIVE: To compare spectral and complexity characteristics of the EEG in a unique case of subcortical infarct to those seen in healthy controls. METHODS: Absolute and relative frequency spectra, theta/beta ratio, the brain symmetry index (BSI), Omega-complexity and synchronization likelihood were calculated of the EEG recorded in eyes closed and eyes open conditions. RESULTS: Increased absolute delta, theta, and Omega-complexity in these frequency bands, higher theta/beta ratios, and decreased relative beta activity were found in the side of the infarct. The BSI localized the excess of slow, and decrease of fast frequency activity to the area of ischemia. Following eyes opening the increase of fast and decrease of slow frequencies, the increase of Omega-complexity in the alpha and beta bands, and the decrease of synchronization likelihood for the fast frequency bands were reduced in the side of the infarct. CONCLUSIONS: The subcortical infarct caused ipsilaterally increased slow, and decreased fast frequency activity accompanied by decreased synchronization of slow, increased synchronization of fast frequencies. Reduced reactivity in the ischemic side was particularly apparent for complexity measures. SIGNIFICANCE: Complexity indices of the EEG are sensitive complementary measures of electrophysiological changes caused by local lesions such as subcortical stroke.

[Psychophysiologic and clinical aspects of EEG synchronization related to cognitive processes]. / A kognitív folyamatokkal osszefuggo EEG-szinkronizáció pszichofiziológiai es klinikai vonatkozásai.

The authors review the various forms of EEG-synchronization with special emphasis on the characteristics of the induced and enhanced rhythms. The suggested role of the various EEG frequency bands in the cognitive processes is demonstrated by examples from the literature. The relationship between linear and nonlinear electrophysiological complexity and EEG synchronization is analyzed, with a touch on the use of Omega-complexity and synchronization likelihood methods. In the present study the EEG recorded during adding and subtracting tasks was analyzed with the above methods. It was found that during the adding task the theta band increased in the frontal area, which may be related to activation of working memory processes. Mapping the scalp-distribution of synchronization likelihood also confirmed increased synchronization in the frontal area in addition to which increased values were found in the left temporo-parietal area. The analysis of linear and nonlinear EEG synchronization associated with cognitive processing is suitable to explore the task-related and region specific features of these events.