Adaptive reorganization of cortical networks in Alzheimer's disease

Objective: The impact of neuronal cell loss associated with Alzheimer's disease (AD) on the network organization of the brain is poorly understood. Here we investigated whether modifications in resting-state functional connectivity (FC) are associated with cognitive function of AD patients. Methods: High-density electroencephalograms (EEGs) were obtained from patients with early stages of AD and elderly healthy controls. Cortical oscillations were reconstructed with an adaptive spatial filter. Maps of imaginary coherence (IC) between brain areas were compared between groups and correlated with cognitive performance. Results: Parietal and medial temporal lobes of AD patients showed a disruption of alpha band FC to the rest of the brain. However, an adaptive extension of the language network to the right hemisphere could be observed in AD patients and was correlated with better verbal fluency. A shift of FC from alpha frequencies to theta frequencies could be observed in a memory network and was associated with better verbal memory performance. Conclusions: Not only dysfunctional but also adaptive network reorganization occurs in early AD. Significance: The network mechanisms for preserved cognitive functioning may inform novel treatment strategies for AD in the future. (C) 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.