Resting brain connectivity: changes during the progress of Alzheimer disease

To investigate alterations in functional connectivity in the resting brain networks in healthy elderly volunteers and patients with mild, moderate, or severe Alzheimer Disease (AD).

This study was approved by the institutional ethics committee, and informed consent was obtained. Forty-six patients with AD and 16 healthy elderly volunteers were prospectively examined. Resting-state functional magnetic resonance imaging was used to detect alterations in posterior cingulate cortex (PCC) functional connectivity through a comparison of the healthy control group with three separate AD groups-mild, moderate, and severe AD. A temporal correlation method was used to obtain PCC connectivity maps.

Dissociated functional connectivity between the PCC and a set of regions, including the visual cortices bilaterally, the inferior temporal cortex, the hippocampus, and especially the medial prefrontal cortex and the precuneus and/or cuneus, was observed in all AD groups. The disruption of connectivity intensified as the stage of AD progression increased. There were also regions that exhibited increased connectivity; these regions extended from left lateralized frontoparietal regions and spread to bilateral frontoparietal regions along with AD progression.

Changes in PCC functional connectivity comprised bidirectional alterations in the resting networks in AD-affected brains, and the impaired resting functional connectivity seemed to change with AD progression. Therefore, alterations in functional connectivity in the default mode network might play a role in the progression of AD.