Neurophysiological imaging techniques in dementia

Abstract

Neurophysiological methods, such as electroencephalography (EEG) and event-related potentials, are useful tools in the investigation of brain cognitive function in normal and pathological conditions, with an excellent time resolution when compared to that of other functional imaging techniques. Advanced techniques using a high number of EEG channels also enable a good spatial resolution to be achieved. This, together with the possibility of integration with other anatomical and functional images, may increase the ability to localize brain functions. Spectral analysis of the resting EEG, which gives information on the integrity of the cortical and subcortical networks involved in the generation of cortical rhythms, has the limitation of low sensitivity and specificity for the type of cognitive impairment. In almost all types of dementia, decreased power of the high frequencies is indeed observed in mild stages, accompanied by increased power of the slow rhythms in the more advanced phases. The sensitivity for the detection of spectral abnormalities is improved by studying centroid modifications. More specific information on the type of dementia can be provided by coherence analysis of the resting EEG, a measure of functional cortico-cortical connections, which has different abnormal patterns in Alzheimer's disease, cerebrovascular dementia and dementia associated with multiple sclerosis. Another tool for improving the assessment of demented patients is the study of EEG activity related to particular tasks, such as event-related potentials and event-related desynchronization/synchronization of the EEG, which allow the study of brain activation during cognitive and motor tasks.

EEG Coherence Obtained From an Auditory Oddball Task Increases With Age

“…Sleepiness and eye movement artifacts may contribute to an overestimation of the coherence (Comi and Leocani, 1999). Because the power in the delta and theta frequency bands was lower in the older subjects than in the younger subjects, as was found before during rest (Duffy et al, 1996), it is unlikely that we are only looking at contamination effects.…”

“…Since the 1970s, EEG coherence during rest (alert state, with eyes closed) has been used as a measure for differentiating normal aging from (early) dementia (Besthorn et al, 1994;Locatelli et al, 1998), dementia from depression (Adler et al, 2003;O'Connor et al, 1979) and different types of dementia, such as Alzheimer disease and multiinfarct dementia, from each other Leuchter et al, 1987Leuchter et al, , 1992. Generally, alpha and beta band coherence are decreased in subjects with dementia when compared with healthy age-matched controls, over both long and short distances during rest (Comi and Leocani, 1999).…”

“…Based on this hypothesis, it will be interesting to complement EEG coherence analysis during rest with the same analysis during cognitive task performance, in patients with memory complaints. Because it has also been shown that both regional and long-range intrahemispheric coherence decrease in Alzheimer disease during rest (Comi and Leocani, 1999;Locatelli et al, 1998), we also studied long-and shortrange intrahemispheric coherence.…”

Discriminating early stage AD patients from healthy controls using synchronization analysis of EEG

“…Using spectral analysis through power and coherence functions, a decrease in local and distant synchronization has been repeatedly shown in AD [7][8][9]. Similarly, the analysis of EEG coherence showed a decrease in long-range synchronization [4,6,[10][11][12][13]. Recently we reported the AD specific whole-head mapping of multivariate synchronization using two methodologically different methods: a state-space based method called S-estimator and multivariate phase synchronization (MPS) measure [5].…”

Spectral Analysis of EEG in Familial Alzheimer’s Disease with E280A Presenilin-1 Mutation Gene

“…Longitudinal analyses of brain EEG rhythms have provided objective evidences of disease progression from MCI to AD [17, 18]. Previous studies using the EEG in demented patients have reported high sensitivity in detecting a diffuse organic damage, but low specificity in determining an etiologic diagnosis [19]. In the last years, several research groups have started investigating the potentiality of electroencephalogram for diagnosis AD.…”