Intrahemispheric, interhemispheric, and distal EEG coherence in Alzheimer's disease

Objectives: This paper presents a comprehensive EEG study for interhemispheric, intrahemispheric, and distal coherence in Alzheimer's disease (AD) patients. The objective is to glean new insights into the brain of AD patients. Methods: EEGs are obtained from 20 AD-probable patients and 7 healthy (control) subjects. Pair-wise electrode coherence is calculated over each frequency band (delta, theta, alpha, and beta). Results: One-way ANOVA test shows a set of statistically significant differences in electrode coherence between AD and controls. In general, AD patients present a significant pattern of increase in the left intrahemispheric frontal coherence in the delta, theta, and alpha bands, an increase in the left intrahemispheric temporo-parietal coherence in all bands, and a decrease in the right temporo-parieto-central coherence in all bands. The increase in left temporo-parietal, temporo-central, and frontal coherence of AD patients in specific bands, being most pronounced in the theta band, could be attributed to compensatory mechanisms that attempt to make up for the decrease in memory and cognitive functions caused by the progression of AD. Conclusions: The coherence study presented in this paper shows a pattern of decrease in AD coherence, indicating a decline in cortical connectivity. Exceptions are seen in specific bands where an increase in coherence can be attributed to compensatory mechanisms. Significance: The research shows that coherence studies have potentials in differentiating between healthy elderly and probable AD patients. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.