Abstract
Background: While decreased alpha and beta-band functional connectivity (FC) and changes in network topology have been reported in Alzheimer’s disease, it is not yet entirely known whether these differences can mark cognitive decline in the early stages of the disease. Our study aimed to analyze electroencephalography (EEG) FC and network differences in the alpha and beta frequency band during visuospatial memory maintenance between Mild Cognitive Impairment (MCI) patients and healthy elderly with subjective memory complaints.Methods: Functional connectivity and network structure of 17 MCI patients and 20 control participants were studied with 128-channel EEG during a visuospatial memory task with varying memory load. FC between EEG channels was measured by amplitude envelope correlation with leakage correction (AEC-c), while network analysis was performed by applying the Minimum Spanning Tree (MST) approach, which reconstructs the critical backbone of the original network.Results: Memory load (increasing number of to-be-learned items) enhanced the mean AEC-c in the control group in both frequency bands. In contrast to that, after an initial increase, the MCI group showed significantly (p < 0.05) diminished FC in the alpha band in the highest memory load condition, while in the beta band this modulation was absent. Moreover, mean alpha and beta AEC-c correlated significantly with the size of medial temporal lobe structures in the entire sample. The network analysis revealed increased maximum degree, betweenness centrality, and degree divergence, and decreased diameter and eccentricity in the MCI group compared to the control group in both frequency bands independently of the memory load. This suggests a rerouted network in the MCI group with a more centralized topology and a more unequal traffic load distribution.Conclusion: Alpha- and beta-band FC measured by AEC-c correlates with cognitive load-related modulation, with subtle medial temporal lobe atrophy, and with the disruption of hippocampal fiber integrity in the earliest stages of cognitive decline. The more integrated network topology of the MCI group is in line with the “hub overload and failure” framework and might be part of a compensatory mechanism or a consequence of neural disinhibition.
Highlights
Deteriorated working memory maintenance and the impairment of visuospatial memory are early symptoms of Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD) (Bird et al, 2010; Parra et al, 2010; Gillis et al, 2013; Moodley et al, 2015) and can serve as a sensitive marker of early cognitive decline (Tierney et al, 1996; Sano et al, 2011)
Post-hoc analysis of this interaction revealed, that the memory load-related modulation of amplitude envelope correlation with leakage correction (AEC-c) followed different dynamics in the two study groups: in the control group compared to the low memory load condition, a significantly increased mean amplitude envelope correlation (AEC)-c was observable in the medium memory load condition and in the high memory load condition and these memory load-related differences remained significant after correction for multiple comparisons
Our results suggest that brain networks of MCI patients show a transient shift to a more centralized, star-like topology to compensate for the initial impairments in accordance with the “hub overload” stage, and complement former EEG studies, which reported the deviation of the network topology from the optimal small-world architecture to a more random type configuration (Wei et al, 2015) and the shifting of the Minimum Spanning Tree (MST) toward a more decentralized, line-like structure of AD patients in the “hub failure” stage during resting state (Yu et al, 2016; Peraza et al, 2018; Das and Puthankattil, 2020) and cognitive tasks (Das and Puthankattil, 2020)
Summary
Deteriorated working memory maintenance and the impairment of visuospatial memory are early symptoms of Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD) (Bird et al, 2010; Parra et al, 2010; Gillis et al, 2013; Moodley et al, 2015) and can serve as a sensitive marker of early cognitive decline (Tierney et al, 1996; Sano et al, 2011). Our study aimed to analyze electroencephalography (EEG) FC and network differences in the alpha and beta frequency band during visuospatial memory maintenance between Mild Cognitive Impairment (MCI) patients and healthy elderly with subjective memory complaints
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
