Reduced precuneus deactivation during object naming in patients with mild cognitive impairment, Alzheimer's disease, and frontotemporal lobar degeneration.

The precuneus is part of the default network of the human brain, which exhibits a high level of activity during the resting state and lower activity during task-related behavior. Typically, the posterior midline areas show this characteristic response in functional magnetic resonance imaging (fMRI) studies. In Alzheimer's disease (AD) and mild cognitive impairment (MCI), subjects exhibit a lack of this typical deactivation. The interpretation of these findings, however, is obfuscated by the presence of local pathology and atrophy in AD. In contrast to AD, in patients with early frontotemporal lobar degeneration (FTLD), the precuneus is virtually free of local neuropathology. In this study, we demonstrate reduced fMRI signal in the precuneus in a group of patients with FTLD during a confrontation naming task. We show that this effect in FTLD patients was (1) similar to that observed in AD and MCI and (2) not related to the degree of gray matter atrophy in the precuneus. We hypothesize that reduced deactivation of the default network is not related to local pathology but to a lack of connectivity, which decreases in both FTLD and AD, the major cortical dementias.