We investigated in a longitudinal multicenter cohort study functional cortical connectivity changes along the course of frontotemporal dementia (FTD) and Alzheimer's disease (AD) from the prodromal stage of the diseases. Electroencephalography (EEG) was recorded in 18 FTD and 18 AD patients at the prodromal stage of dementia, at dementia onset, and 3 years after dementia onset. Twenty healthy controls (HC) underwent EEG recordings at the same time interval as the patients. Mutual information (MI) analysis measured the strength of functional network connectivity. FTD and AD patients showed greater MI at the prodromal stage of dementia (FTD vs. HC P = 2 × 10-8; AD vs. HC P = 4 × 10-3). Local connectivity was higher in left and right frontal areas of FTD (P = 7 × 10-5 and 0.03) and in left and right posterior areas in AD (P = 3 × 10-5 and 5 × 10-5) versus HC. We showed cortical hyperconnectivity at the prodromal stage of dementia in areas involved in the specific pathological process of FTD (frontal regions) and AD (posterior regions). Hyperconnectivity disappeared during follow-up, thus suggesting that it is an early electrophysiological feature of dementia, potentially useful to identify prodromal FTD and AD.
