Beau Ances, assistant professor of neurology, Washington University School of Medicine in St. Louis, who led the study said: "Communications within and between networks are disrupted, but it doesn`t happen all at once."
"There`s even one network that has a momentary surge of improved connections before it starts dropping again.
"That`s the salience network, which helps you determine what in your environment you need to pay attention to," added Ances, The Journal of Neuroscience reported.
Ances and colleagues analyzed brain scans of 559 subjects.
Some of these subjects were cognitively normal, while others were in the early stages of very mild to mild Alzheimer`s disease.
Scientists found that all of the networks they studied eventually became impaired during the initial stages of Alzheimer`s, according to a university statement.
Scientists also examined Alzheimer`s effects on a brain networking property known as anti-correlations.
Researchers identify networks by determining which brain areas frequently become active at the same time, but anti-correlated networks are noteworthy for the way their activities fluctuate: when one network is active, the other network is quiet.
This ability to switch back-and-forth between networks is significantly diminished in participants with mild to moderate Alzheimer`s disease.
The default mode network, previously identified as one of the first networks to be impaired by Alzheimer`s, is a partner in two of the three pairs of anti-correlated networks scientist studied.
"There are, however, a number of additional networks besides the default mode network that become active when the brain is idling and could tell us important things about Alzheimer`s effects," said Ances.
It`s not practical to use these network breakdowns to clinically diagnose Alzheimer`s disease, Ances notes, but they may help track the development of the disease and aid efforts to better understand its spread through the brain.
Ances plans to look at other markers for Alzheimer`s disease in the same subjects, such as levels in the cerebrospinal fluid of amyloid beta, a major component of Alzheimer`s plaques.