Dementia: The Networking Brain Breaks Down

(Image: George Mattei / SPL)

The network structure of healthy brains allows very efficient communication between different brain regions.

YOU might expect the brain of someone with a mental disorder to be disorganised. But it's the nature of the disorganisation that's important - a finding that one day could help early diagnosis of different types of dementia.

We already know that the different regions of healthy brains are linked in a so-called small-world network, which makes communication very efficient. For people with Alzheimer's or other types of dementia, however, it's a different story.

In small-world networks - which also emerge, for example, in social networks - each node is connected to a lot of nearby nodes, but also has a few links to distant ones. Because of this, any node can communicate with almost any other in just a few hops.

This may explain the brain's formidable ability to process masses of information rapidly. "A small world, in theoretical terms, is the optimal network," says Willem de Haan of the VU University Medical Center in Amsterdam, the Netherlands.

De Haan's team used scalp electrodes to measure the brain activity of resting volunteers, of whom 20 had mild to moderate Alzheimer's, 15 had a rare form of dementia called frontal temporal lobe dementia (FTLD), and 23 were healthy. The researchers figured out the underlying network structure of the volunteers' brains from the electrical activity in different regions over time.

In healthy brains, this structure resembled a small-world network, as expected. In people with Alzheimer's, the nodes were connected more randomly; in FTLD, the network was more ordered, with fewer long-distance links. The researchers think that in both abnormal cases the brain networks would be less efficient at exchanging information, and that this might explain some of the cognitive problems experienced by people with these disorders (BMC Neuroscience, DOI: 10.1186/1471-2202-10-101).