The brain can be viewed as a complex neural network consisting of structurally and functionally interconnected regions at multiple scales (Panel 1).12 At the macroscopic level, neural networks can be investigated non-invasively in health and disease with functional MRI and neurophysiological techniques (electro- and magneto-encephalography, EEG and MEG).13,14 The aim of this review is to provide a comprehensive overview of findings on functional network disruption in the most prevalent neurodegenerative dementias. Although several excellent reviews have addressed functional networks disruption in AD and in psychiatric conditions,15-20 here we summarize studies across multiple neurodegenerative dementias. By including FTD, PD dementia and DLB, we highlight functional network similarities and differences among conditions that share common mechanisms (toxic protein aggregation and neuronal loss) but have distinct clinical phenotypes. Toward this aim, resting-state “task-free” functional imaging and neurophysiological studies will be reviewed. Because our primary goal is to review functional methods that are broadly applicable across neurodegenerative diseases, we have omitted task-activation studies, which require the design of disease-specific experiments (for a review of its applications in AD, see Dickerson 2007),21 as well as studies of gray matter structural covariance.22,23
