http://www.newscientist.com/article/dn26206-brains-can-power-up-to-get-around-alzheimers-plaques.html?#.VBboYWOVCug
A couple of paragraphs, rest at link.
Jagust found that older people with plaques had increased blood flow – which means stronger activation of that brain area – in the regions of the brain that are usually activated during memory formation, compared with the older people who did not have plaques. The team then analysed whether this extra brain activation might be helping to compensate for the plaques.
And the results were clear. In the case of the older
people with beta-amyloid, the more accurate their memory of the picture,
the more active their brain had been when they studied the image in
the fMRI. "That suggested to us that they were able to ramp up activity
to retain more information," says Jagust. "We interpret this as a
compensation or plasticity. The older people who didn't have amyloid in
the brain did not do it."
This boosting of brain
activity seems to be related to the amount of plaques a person had. The
more beta-amyloid protein someone had, the more they tended to ramp up
their brain activity while memorising the scene. However, this effect
tailed off in the people with the greatest amount of plaques. "It
suggests this is a transitory phenomenon. Eventually, this sort of
compensation becomes lost. And that might be something that happens in
the progression to cognitive decline," Jagust says.
The results could also help explain why some people have the plaques
without appearing to have dementia. "The fact that brain amyloid is
detectable in cognitively normal elderly subjects has been used
historically as an argument to support the idea that amyloid may not be
as toxic as suggested by experimental studies," says Roger Nitsch,
a neuroscientist at the University of Zurich in Switzerland. "This work
challenges this view by addressing how elderly subjects can retain
normal cognition despite the presence of brain amyloid."
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