“Small World” architecture in brain connectivity and hippocampal volume in Alzheimer’s disease: a study via graph theory from EEG data
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Brain imaging plays an important role in the study of Alzheimer’s disease (AD), where atrophy has been found to occur in the hippocampal formation during the very early disease stages and to progress in parallel with the disease’s evolution. The aim of the present study was to evaluate a possible correlation between “Small World” characteristics of the brain connectivity architecture—as extracted from EEG recordings—and hippocampal volume in AD patients. A dataset of 144 subjects, including 110 AD (MMSE 21.3) and 34 healthy Nold (MMSE 29.8) individuals, was evaluated. Weighted and undirected networks were built by the eLORETA solutions of the cortical sources’ activities moving from EEG recordings. The evaluation of the hippocampal volume was carried out on a subgroup of 60 AD patients who received a high-resolution T1-weighted sequence and underwent processing for surface-based cortex reconstruction and volumetric segmentation using the Freesurfer image analysis software. Results showed that, quantitatively, more correlation was observed in the right hemisphere, but the same trend was seen in both hemispheres. Alpha band connectivity was negatively correlated, while slow (delta) and fast-frequency (beta, gamma) bands positively correlated with hippocampal volume. Namely, the larger the hippocampal volume, the lower the alpha and the higher the delta, beta, and gamma Small World characteristics of connectivity. Accordingly, the Small World connectivity pattern could represent a functional counterpart of structural hippocampal atrophying and related-network disconnection.
KeywordsGraph theory Alzheimer Functional connectivity EEG Hippocampus eLORETA MRI
Dr. Francesca Miraglia participated to this study in the framework of her Ph.D. program at the Doctoral School in Neuroscience, Department of Neuroscience, Catholic University of Rome, Italy. This work was supported by the Italian Ministry of Health for Institutional Research (Ricerca corrente) and by the Italian Ministry of Instruction, University and Research MIUR (“Approccio integrato clinico e sperimentale allo studio dell’invecchiamento cerebrale e delle malattie neurodegenerative: basi molecolari, epidemiologia genetica, neuroimaging multimodale e farmacogenetica. (Merit)” and “Functional connectivity and neuroplasticity in physiological and pathological aging. Prot. 2010SH7H3F (ConnAge)” PRIN project).
Compliance with ethical standards
This work was supported by the Italian Ministry of Health for Institutional Research (Ricerca corrente) and by the Italian Ministry of Instruction, University and Research MIUR (“Approccio integrato clinico e sperimentale allo studio dell’invecchiamento cerebrale e delle malattie neurodegenerative: basi molecolari, epidemiologia genetica, neuroimaging multimodale e farmacogenetica. (Merit)” and “Functional connectivity and neuroplasticity in physiological and pathological aging. Prot. 2010SH7H3F (ConnAge)” PRIN project).
Conflict of interest
All authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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