Alpha-Band Hypersynchronization in Progressive Mild Cognitive Impairment: A Magnetoencephalography Study

Abstract

People with mild cognitive impairment (MCI) show a high risk to develop Alzheimer's disease (AD; Petersen et al., 2001). Nonetheless, there is a lack of studies about how functional connectivity patterns may distinguish between progressive (pMCI) and stable (sMCI) MCI patients. To examine whether there were differences in functional connectivity between groups, MEG eyes-closed recordings from 30 sMCI and 19 pMCI subjects were compared. The average conversion time of pMCI was 1 year, so they were considered as fast converters. To this end, functional connectivity in different frequency bands was assessed with phase locking value in source space. Then the significant differences between both groups were correlated with neuropsychological scores and entorhinal, parahippocampal, and hippocampal volumes. Both groups did not differ in age, gender, or educational level. pMCI patients obtained lower scores in episodic and semantic memory and also in executive functioning. At the structural level, there were no differences in hippocampal volume, although some were found in left entorhinal volume between both groups. Additionally, pMCI patients exhibit a higher synchronization in the alpha band between the right anterior cingulate and temporo-occipital regions than sMCI subjects. This hypersynchronization was inversely correlated with cognitive performance, both hippocampal volumes, and left entorhinal volume. The increase in phase synchronization between the right anterior cingulate and temporo-occipital areas may be predictive of conversion from MCI to AD.

Consistency of magnetoencephalographic functional connectivity and network reconstruction using a template versus native MRI for co‐registration

“…The lowest consistency for global parameters averaged across subjects was observed for the MST leaf fraction and diameter, although these still yielded moderate to very good consistency in this relatively small sample. Owing to the higher order nature of these network measures, we expected their consistency to decrease nonlinearly: a basic, robust measure such as relative power will only be slightly affected by reconstruction errors [Beg et al, ; López et al, ; Steinstraeter et al, ]. However, these inconsistencies could be augmented in the next step of determining phase correlations.…”

“…Several studies have already employed a template‐based method for source localization in the absence of native MRIs. For instance, López et al [] have used a template generated from MRIs of healthy controls for source reconstruction to perform connectivity analysis. Holliday et al [] selected the MRI with closest matching external head shape from a database, and used it as a substitute for the subject's own MRI.…”

Healthy and Pathological Brain Aging: From the Perspective of Oscillations, Functional Connectivity, and Signal Complexity

“…Thus, the intrinsic network organization at rest allows the brain to allocate resources and ready itself for changes in response to stimuli [29]. An increase in DMN alpha functional connectivity in patients with MCI shows a correlation with HA and entorhinal atrophy [68]. A hypersynchronization pattern in MCI patients was also found in a recent blinded, multicenter MEG study.…”

“…An increasing number of studies report a pattern of hypersynchronization, specifically in the alpha frequency band, between certain brain regions in MCI or prodromal AD which is associated with cognitive decline. This increase in alpha synchronization mainly affects the temporal cortex and regions of the default mode network (DMN) [68]. This network is active during the resting state and is temporally interrupted or attenuated during the performance of cognitive tasks.…”

Multimodal Oscillation-based Connectivity Theory

“…By analyzing data recorded during a memory task they reported increased synchronization values in the alpha 1 and 2 frequency bands over the posterior parieto-occipital regions and in prefrontal regions in MCI patients who subsequently convert to AD, in comparison to non-converters. In a subsequent study, López et al (2014) assessed whether these profiles can be reproduced during a resting-state condition. MCI converters showed increased connectivity between the anterior cingulate cortex and the posterior brain regions.…”