Decreased EEG synchronization in Alzheimer’s disease and mild cognitive impairment
ABSTRACT The hypothesis of a functional disconnection of neuro-cognitive networks in patients with mild cognitive impairment (MCI) and Alzheimer Dementia was investigated using baseline resting EEG data. EEG databases from New York (264 subjects) and Stockholm (155 subjects), including healthy controls and patients with varying degrees of cognitive decline or Alzheimer Dementia were analyzed using Global Field Synchronization (GFS), a novel measure of global EEG synchronization. GFS reflects the global amount of phase-locked activity at a given frequency by a single number; it is independent of the recording reference and of implicit source models. Patients showed decreased GFS values in Alpha, Beta, and Gamma frequency bands, and increased GFS values in the Delta band, confirming the hypothesized disconnection syndrome. The results are discussed within the framework of current knowledge about the functional significance of the affected frequency bands.
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- "While theta and alpha ITC were larger in both control groups as compared to MCI, beta ITC distinguished the two groups of control subjects, with decreased values in dCON and MCI as compared to sCON, although differences with MCI remained just below significance probably because of the elevated inter-individual variability in this group. Overall, these observations are in line with most connectivity studies in MCI/AD patients, generally reporting reduced 4–30 Hz coherence among cortical regions in MCI/AD compared to elderly controls at rest, compatible with the disconnection syndrome      . Moreover, some studies emphasize the greater sensitivity of the beta frequency band, describing reduced resting beta synchronization in MCI and AD that correlates with neuropsychological testing  . "
ABSTRACT: Future treatments of Alzheimer's disease need the identification of cases at high risk at the preclinical stage of the disease before the development of irreversible structural damage. We investigated here whether subtle cognitive deterioration in a population of healthy elderly individuals could be predicted by EEG signals at baseline under cognitive activation. Continuous EEG was recorded in 97 elderly control subjects and 45 age-matched mild cognitive impairment (MCI) cases during a simple attentional and a 2-back working memory task. Upon 18-month neuropsychological follow-up, the final sample included 55 stable (sCON) and 42 deteriorated (dCON) controls. We examined the P1, N1, P3, and PNwm event-related components as well as the oscillatory activities in the theta (4-7 Hz), alpha (8-13 Hz), and beta (14-25 Hz) frequency ranges (ERD/ERS: event-related desynchronization/synchronization, and ITC: inter-trial coherence). Behavioral performance, P1, and N1 components were comparable in all groups. The P3, PNwm, and all oscillatory activity indices were altered in MCI cases compared to controls. Only three EEG indices distinguished the two control groups: alpha and beta ERD (dCON > sCON) and beta ITC (dCON < sCON). These findings show that subtle cognitive deterioration has no impact on EEG indices associated with perception, discrimination, and working memory processes but mostly affects attention, resulting in an enhanced recruitment of attentional resources. In addition, cognitive decline alters neural firing synchronization at high frequencies (14-25 Hz) at early stages, and possibly affects lower frequencies (4-13 Hz) only at more severe stages.Journal of Alzheimer's disease: JAD 07/2015; 47(2). DOI:10.3233/JAD-150111 · 4.15 Impact Factor
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- "These EEG abnormalities were associated with altered regional cerebral blood flow/metabolism and with impaired global cognitive function as evaluated by the Minimental state examination (MMSE) (Sloan et al., 1995; Rodriguez et al., 1998, 1999a,b; Jeong, 2004). In the same vein, MCI subjects showed a decrease of alpha rhythms compared to normal elderly subjects (Zappoli et al., 1995; Elmstáhl and Rosén, 1997; Huang et al., 2000; Jelic et al., 2000; Koenig et al., 2005). Of note, these EEG markers were found to be related to MRI markers indexing brain atrophy as revealed by hippocampus (Babiloni et al., 2009), normalized volume of cortical gray matter (Babiloni et al., 2013), and cortical gray matter density (Babiloni et al. in press). "
ABSTRACT: Amnesic mild cognitive impairment (MCI) represents a risk of developing Alzheimer's disease (AD), but not all MCI subjects progress to dementia of AD type. Magnetic resonance imaging (MRI) of cortical and hippocampal atrophy supports early diagnosis of AD in MCI subjects, while frontal event-related oscillations (EROs) at delta frequencies (<4Hz) are appealing markers for this purpose, as they are both cost-effective and largely available (Başar et al., 2014 in this issue). The present study tested the hypothesis that these EROs reflect cortical frontal neurodegeneration in the continuum between normal and amnesic MCI subjects. EROs and volumetric MRI data were recorded in 28 amnesic MCI and in 28 healthy elderly controls (HCs). EROs were collected during a standard visual oddball paradigm including frequent (66.6%) and rare (33.3%; targets to be mentally counted) stimuli. Peak-to-peak amplitude of delta target EROs (<4Hz) was measured. Volume of the frontal cortex was estimated from MRIs. Frontal volume was lower in MCI compared to the HC group. Furthermore, widespread delta target EROs were lower in amplitude in the former than in the latter group. Finally, there was a positive correlation between frontal volume and frontal delta target EROs in MCI and HC subjects as a whole group. These results suggest that frontal delta EROs reflect frontal neurodegeneration in the continuum between normal and amnesic MCI subjects. Copyright © 2015. Published by Elsevier B.V.International journal of psychophysiology: official journal of the International Organization of Psychophysiology 02/2015; DOI:10.1016/j.ijpsycho.2015.02.005 · 2.88 Impact Factor
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- "These EEG abnormalities are associated with altered regional cerebral blood flow and/or metabolism and with impaired global cognitive function as evaluated by the mini mental state examination (MMSE; Jeong, 2004; Rodriguez et al., 1998, 1999a, 1999b; Sloan et al., 1995). Similarly, MCI subjects show a decrease of alpha rhythms compared with normal elderly subjects (Elmstahl and Rosen, 1997; Huang et al., 2000; Jelic et al., 2000; Koenig et al., 2005; Zappoli et al., 1995). However , a certain variability of the brain rhythms in pathologic aging might prevent its use for personalized diagnosis and prognosis, especially in early MCI. "
ABSTRACT: Occipital sources of resting-state electroencephalographic (EEG) alpha rhythms are abnormal, at the group level, in patients with amnesic mild cognitive impairment (MCI) and Alzheimer's disease (AD). Here, we evaluated the hypothesis that amplitude of these occipital sources is related to neurodegeneration in occipital lobe as measured by magnetic resonance imaging. Resting-state eyes-closed EEG rhythms were recorded in 45 healthy elderly (Nold), 100 MCI, and 90 AD subjects. Neurodegeneration of occipital lobe was indexed by weighted averages of gray matter density, estimated from structural MRIs. EEG rhythms of interest were alpha 1 (8-10.5 Hz) and alpha 2 (10.5-13 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography. Results showed a positive correlation between occipital gray matter density and amplitude of occipital alpha 1 sources in Nold, MCI, and AD subjects as a whole group (r = 0.3, p = 0.000004, N = 235). Furthermore, there was a positive correlation between the amplitude of occipital alpha 1 sources and cognitive status as revealed by Mini Mental State Examination score across all subjects (r = 0.38, p = 0.000001, N = 235). Finally, amplitude of occipital alpha 1 sources allowed a moderate classification of individual Nold and AD subjects (sensitivity: 87.8%; specificity: 66.7%; area under the receiver operating characteristic curve: 0.81). These results suggest that the amplitude of occipital sources of resting-state alpha rhythms is related to AD neurodegeneration in occipital lobe along pathologic aging. Copyright © 2014 Elsevier Inc. All rights reserved.Neurobiology of Aging 09/2014; DOI:10.1016/j.neurobiolaging.2014.09.011 · 5.01 Impact Factor