In asymptomatic autosomal dominant Alzheimer’s disease carriers with detectable tau pathology, increased functional connectivity in the default mode network—including the posterior cingulate, precuneus, and bilateral temporal regions—is associated with tau deposition, while reduced functional connectivity is observed in the left medial inferior temporal cortex and fusiform gyrus, indicating early network reorganization prior to cognitive decline.

When tau protein builds up in key brain areas that handle memory and self-referential thinking, those areas initially increase their communication with nearby regions to keep functioning normally. This causes some parts of the brain to become overconnected. At the same time, other areas that connect to these tau-affected regions lose their ability to communicate properly. This pattern of increased and decreased connections happens before any memory problems appear.