Scientists at Washington University School of Medicine in St. Louis have taken one of the first detailed looks into how Alzheimer's disease disrupts coordination among several of the brain's networks. The results include some of the earliest assessments of Alzheimer's effects on networks that are active when the brain is at rest.

"Until now, most research into Alzheimer's effects on brain networks has either focused on the networks that become active during a mental task, or the default mode network, the primary network that activates when a person is daydreaming or letting the mind wander," says senior author Dr. Beau Ances, assistant professor of neurology. "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."

Ances and his colleagues analyzed brain scans of 559 subjects. Some of those subjects were cognitively normal, while others were in the early stages of mild Alzheimer's disease. Scientists found that all of the networks they studied eventually became impaired during the initial stages of Alzheimer's.

"Communications within and between networks are disrupted, but it doesn't happen all at once," Ances says.

Other networks studied by the researchers included the dorsal attention network, which directs attention toward things in the environment that are salient; the control network, believed to be active in consciousness and decision-making; and the sensory-motor network, which integrates the brain's control of body movements with sensory feedback.

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. 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.

"While we can't prove this yet, one hypothesis is that as things go wrong in the processing of information in the default mode network, that mishandled data is passed on to other networks, where it creates additional problems," Ances says.