Regional coherence evaluation in mild cognitive impairment and Alzheimer's disease based on adaptively extracted magnetoencephalogram rhythms

Abstract

Abstract. This study assesses the connectivity alterations caused by Alzheimer's disease (AD) and mild cognitive impairment (MCI) in the magnetoencephalogram (MEG) background activity. Moreover, a novel methodology to adaptively extract brain rhythms from the MEG is introduced. This methodology relies on the ability of an Empirical Mode Decomposition (EMD) to isolate local signal oscillations and a constrained Blind Source Separation (cBSS) to extract the activity that jointly represents a subset of channels. Inter-regional MEG connectivity was analysed for 36 AD, 18 MCI, and 26 control subjects in δ, θ, α, and β bands over left and right central, anterior, lateral, and posterior regions with magnitude squared coherence -c(f ). For the sake of comparison, c(f ) was calculated from the original MEG channels and from the adaptively extracted rhythms. The results indicated that AD and MCI cause slight alterations in the MEG connectivity. c(f ) computed from the extracted rhythms distinguished AD and MCI subjects from controls with 69.4% and 77.3% accuracies, respectively, in a full leave-one-out cross-validation evaluation. These values were higher than those obtained without the proposed extraction methodology.

Analysis of spontaneous MEG activity in mild cognitive impairment and Alzheimer's disease using spectral entropies and statistical complexity measures

“…Thus, an early AD diagnosis should be established on the basis of a previous MCI detection. Our findings suggest that MCI exhibit intermediate alterations between AD and normal aging, which agrees with the results of previous research (Fernandez et al 2006, 2010, Escudero et al 2011. Previous MEG studies reported classification rates of AD patients versus elderly controls about 80% (Fernandez et al 2006, Poza et al 2007, Gomez et al 2009a, Hornero et al 2009, Stam 2010, Alonso et al 2011, Escudero et al 2011.…”

“…Our classification results are similar to this value, since the highest accuracy was 83.9%. On the other hand, previous MEG studies usually reached an accuracy about 65% to discriminate between MCI and control subjects (Fernandez et al 2006, 2010, Gomez et al 2009a, Escudero et al 2011. Our highest accuracy was 65.9%.…”

“…The results in the upper bands were not conclusive, but a slight reduction in alpha interregional connectivity was found. On the other hand, only subtle differences have been reported between MCI and control subjects (Fernandez et al 2006, 2010, Gomez et al 2009b, Escudero et al 2011. The results in these studies indicated that MCI subjects show intermediate abnormalities between AD patients and elderly controls.…”

“…A slight increase in low frequency power of AD patients in comparison to MCI subjects has been found in previous studies (Fernandez et al 2006, Osipova et al 2006, whereas an increase of complexity has been observed in MCI subjects using nonlinear measures . In addition, different patterns of connectivity between both groups have been found in studies based on functional connectivity (Escudero et al 2011). Their results suggested that AD increases the level of coherence in the delta band, while MCI subjects tend to have lower connectivity in theta band.…”

Complexity of functional connectivity networks in mild cognitive impairment subjects during a working memory task

“…Decreasing posterior alpha power in MCI patients (Babiloni et al, 2008), gray matter loss in temporal, parietal, and frontal regions (Karas et al, 2004;Barbeau et al, 2008) and increased activity of occipital regions in MCI subjects during incremental learning (Moulin et al, 2007) are some of the major findings previously reported. Although there are some studies on functional connectivity of MCI's brain (Gómez et al, 2009;Escudero et al, 2011), only a few researchers have investigated the global organization of brain networks in MCI (de Haan et al, 2012).…”