Abstract
We analyzed the relation of several synchrony markers in the electroencephalogram (EEG) and Alzheimer’s disease (AD) severity as measured by Mini-Mental State Examination (MMSE) scores. The study sample consisted of 79 subjects diagnosed with probable AD. All subjects were participants in the PRODEM-Austria study. Following a homogeneous protocol, the EEG was recorded both in resting state and during a cognitive task. We employed quadratic least squares regression to describe the relation between MMSE and the EEG markers. Factor analysis was used for estimating a potentially lower number of unobserved synchrony factors. These common factors were then related to MMSE scores as well. Most markers displayed an initial increase of EEG synchrony with MMSE scores from 26 to 21 or 20, and a decrease below. This effect was most prominent during the cognitive task and may be owed to cerebral compensatory mechanisms. Factor analysis provided interesting insights in the synchrony structures and the first common factors were related to MMSE scores with coefficients of determination up to 0.433. We conclude that several of the proposed EEG markers are related to AD severity for the overall sample with a wide dispersion for individual subjects. Part of these fluctuations may be owed to fluctuations and day-to-day variability associated with MMSE measurements. Our study provides a systematic analysis of EEG synchrony based on a large and homogeneous sample. The results indicate that the individual markers capture different aspects of EEG synchrony and may reflect cerebral compensatory mechanisms in the early stages of AD.
Highlights
Alzheimer’s diseaseDementia is a disorder of cognitive abilities that has increasing prevalence with age
The following 8 EEG markers were analyzed in a resting and a cognitively active phase: coherence C, partial coherence pC, phase shift nU, Granger causality G, conditional Granger causality cG, canonical correlation qc, dynamic canonical correlation dqc,and cross-mutual information cMI
We analyzed and compared different EEG synchrony markers in Alzheimer’s disease (AD) patients both in a resting and a cognitively active state and how these markers changed with AD severity as measured by Mini-Mental State Examination (MMSE) scores
Summary
Dementia is a disorder of cognitive abilities that has increasing prevalence with age. Alzheimer’s disease (AD) is estimated to account for 60–80 % of dementia cases; hybrid forms with other dementia types occur frequently (Schmidt et al 2010; Jellinger 2007). AD is a progressive brain disorder that is associated with neuronal cell loss and the development of neurofibrillary tangles and cortical amyloid plaques, e.g., in the hippocampus (Braak et al 2006). Alterations in transmitter-specific markers including forebrain cholinergic systems are prevalent in AD (McKhann et al 2011). Cognitive deficits include impairment of learning and memory, semantic difficulties, deficits in judgement, abstract or logical reasoning, planning and organizing, and, in the late stage of AD, impaired motor functions including chewing and swallowing.
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