Adaptive reorganization of cortical networks in Alzheimer’s disease

ObjectiveThe 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.MethodsHigh-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.ResultsParietal 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.ConclusionsNot only dysfunctional but also adaptive network reorganization occurs in early AD.SignificanceThe network mechanisms for preserved cognitive functioning may inform novel treatment strategies for AD in the future.

► Patients with Alzheimer’s disease have a profound disruption of alpha-band coherence in the same regions that are also most affected by atrophy and amyloid deposition.
► Patients with Alzheimer’s disease also present adaptive network reorganization associated with relatively preserved cognitive function.
► Two different mechanisms of network plasticity: extension to contralateral brain regions and slowing of coherent oscillations.