Many people with Alzheimer's disease have a tendency to sleep a lot during the day, even when they have had a full night's sleep.

Based on links between excessive sleepiness and neurodegenerative conditions, researchers are speculating that looking at daytime napping patterns could help predict the development of Alzheimer's.

But what remains unclear is why, exactly, people with this condition experience the need to sleep so often.

A new study, conducted by researchers at the University of California, San Francisco (UCSF) and other institutions, shows that people with Alzheimer's disease experience major brain cell loss in regions of the brain tasked with keeping us awake.

The findings, which appear in the journal Alzheimer's & Dementia, also suggest that an overaccumulation of tau protein triggers these brain changes.

In Alzheimer's disease, tau proteins form tangles that disrupt communication between neurons (brain cells) and impact cell health.

"Our work shows definitive evidence that the brain areas promoting wakefulness degenerate due to accumulation of tau — not amyloid protein [another protein that can become toxic in Alzheimer's disease] — from the very earliest stages of the disease," explains senior author Dr. Lea Grinberg.

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