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takyon writes:

Alzheimer's protein may spread like an infection, human brain scans suggest

For the first time, scientists have produced evidence in living humans that the protein tau, which mars the brain in Alzheimer's disease, spreads from neuron to neuron. Although such movement wasn't directly observed, the finding may illuminate how neurodegeneration occurs in the devastating illness, and it could provide new ideas for stemming the brain damage that robs so many of memory and cognition.

[...] Researchers at the University of Cambridge in the United Kingdom combined two brain imaging techniques, functional magnetic resonance imaging and positron emission tomography (PET) scanning, in 17 Alzheimer's patients to map both the buildup of tau and their brains' functional connectivity—that is, how spatially separated brain regions communicate with each other. Strikingly, they found the largest concentrations of the damaging tau protein in brain regions heavily wired to others, suggesting that tau may spread in a way analogous to influenza during an epidemic, when people with the most social contacts will be at greatest risk of catching the disease.

The research team says this pattern, described yesterday in Brain [open, DOI: 10.1093/brain/awx347] [DX], supports something known as the "transneuronal spread" hypothesis for Alzheimer's disease, which had previously been demonstrated in mice but not people. "We come down quite strongly in favor of the idea that tau is starting in one place and moving across neurons and synapses to other places," says clinical neurologist Thomas Cope, one of the study's authors. "That has never before been shown in humans. That's very exciting." Because the researchers looked at Alzheimer's patients with a range of disease severity, they were also able to demonstrate that, when tau accumulation was higher, brain regions were on the whole less connected. The strength of connections also decreased, and connections were increasingly random.

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