A multi-year study involving 207 healthy older adults, in which their spinal fluids were repeatedly sampled and their brains repeatedly scanned, has found that disruptions in the default mode network emerges about the same time as chemical markers of Alzheimer’s appear in the spinal fluid (decreased amyloid-beta and increased tau protein). The finding suggests not only that amyloid-beta and tau pathology affect default mode network integrity early on, but that scans of brain networks may be an equally effective and less invasive way to detect early disease.
The greatest decrease in functional connectivity was found between the posterior cingulate and medial temporal regions. This decrease was not attributable to age or structural atrophy in these regions.
 Cerebrospinal fluid aβ42, phosphorylated tau181, and resting-state functional connectivity. JAMA Neurology. 70(10), 1242 - 1248.(2013).