Quantitative characteristics of EEG in Alzheimer’s disease during cognitive tasks

In Alzheimer’s disease (AD) the EEG changes are rather diffuse and most expressed in moderate and severe cognitive disorders. Pathological changes of spectral power and EEG coherence are assumed to be related with the degree of cognitive deficit. The aim of this study: comparative analysis of spectral power and EEG coherence and their reactivity during functional tasks in AD patients with mild and moderate dementia and in agematched healthy control subjects. Twenty two AD patients with mild-to-moderate dementia and 25 controls were examined. All patients underwent EEG recordings with analysis of spectral power of the main rhythms, as well as with analysis of intra- and inter-hemispheric coherence and their dynamics during functional tasks. We found an increase in slow-wave activity (delta and theta rhythms) and a decrease in alpha activity in frontal, parietal and temporal regions of the brain. Intra- and interhemispheric coherence was significantly lower in frontal, parietal and temporal regions in AD patients compared to controls. EEG pattern was more obvious after functional tests. One may conclude that changes of spectral power and EEG coherence seem to be a sensitive indicator of cognitive decline at very early stages of neurodegenerative process.