Abnormalities of resting-state functional cortical connectivity in patients with dementia due to Alzheimer's and Lewy body diseases: an EEG study

Abstract

Previous evidence showed abnormal posterior sources of resting-state delta (<4 Hz) and alpha (8-12 Hz) rhythms in patients with Alzheimer's disease with dementia (ADD), Parkinson's disease with dementia (PDD), and Lewy body dementia (DLB), as cortical neural synchronization markers in quiet wakefulness. Here, we tested the hypothesis of additional abnormalities in functional cortical connectivity computed in those sources, in ADD, considered as a "disconnection cortical syndrome", in comparison with PDD and DLB. Resting-state eyes-closed electroencephalographic (rsEEG) rhythms had been collected in 42 ADD, 42 PDD, 34 DLB, and 40 normal healthy older (Nold) participants. Exact low-resolution brain electromagnetic tomography (eLORETA) freeware estimated the functional lagged linear connectivity (LLC) from rsEEG cortical sources in delta, theta, alpha, beta, and gamma bands. The area under receiver operating characteristic (AUROC) curve indexed the classification accuracy between Nold and diseased individuals (only values >0.7 were considered). Interhemispheric and intrahemispheric LLCs in widespread delta sources were abnormally higher in the ADD group and, unexpectedly, normal in DLB and PDD groups. Intrahemispheric LLC was reduced in widespread alpha sources dramatically in ADD, markedly in DLB, and moderately in PDD group. Furthermore, the interhemispheric LLC in widespread alpha sources showed lower values in ADD and DLB than PDD groups. At the individual level, AUROC curves of LLC in alpha sources exhibited better classification accuracies for the discrimination of ADD versus Nold individuals (0.84) than for DLB versus Nold participants (0.78) and PDD versus Nold participants (0.75). Functional cortical connectivity markers in delta and alpha sources suggest a more compromised neurophysiological reserve in ADD than DLB, at both group and individual levels.

Weighted network measures reveal differences between dementia types: An EEG study

“…Here the authors associated the reduced hubness with a more severe cognitive impairment in DLB (van Dellen et al, ). In a more recent study, Babiloni and colleagues reported reduced interhemispheric connectivity patterns in dementia patients (Babiloni et al, ), with weaker connections in AD compared with DLB over posterior and temporal regions within the α range; this intra‐hemispheric connection showed no differences between DLB and PDD. According to the authors, this aspect is associated with the fact that the pathology is similar in both LBDs, that is, DLB and PDD.…”

Genetic Association Between Alzheimer’s Disease Risk Variant of the PICALM Gene and EEG Functional Connectivity in Non-demented Adults

“…LLC characteristics of EEG connectivity are not affected by the instantaneous propagation of neural ionic currents that are partly due to head volume conduction effects. The LLC of posterior alpha sources was found to be decreased in patients with aMCI compared to normal controls (Babiloni et al, 2018).…”

“…The hippocampus is an important node of the DMN that modulates EEG alpha activity. The DMN regions, and the hippocampus in particular, are preferentially vulnerable to degenerative processes that are accompanied by progressive decreases in LLC of alpha sources (Babiloni et al, 2018). In MCI and prodromal AD, alpha disconnection in brain networks is related to progressive cognitive impairment.…”

“…To determine the cortical ROIs, eLORETA defined the MNI coordinates of the cortical voxels underlying the electrode sites. Detailed information on the eLORETA connectivity algorithm has been previously published (Pascual-Marqui et al, 2011;Babiloni et al, 2018). The 16 cortical ROIs determined by eLORETA are shown in Table 2.…”

“…Functional EEG and MEG connectivity is estimated in time and in frequency domains using linear (e.g., correlation, coherence) and non-linear (e.g., lagged phase synchronization, mutual information) methods (Sakkalis, 2011;Núñez et al, 2019). The reduction of functional connectivity assessed by these methods was shown to be related to the severity of dementia in AD patients (Babiloni et al, 2018). A less pronounced decrease in functional connectivity was observed in patients with amnestic mild cognitive impairment (aMCI), which is, in most cases, a prodromal stage of AD.…”