Disrupted deep sleep has been linked to the accumulation of tau protein in the brain, one of the key markers of Alzheimer's disease, and to worsening memory, according to researchers at the University of California, Berkeley. The findings were published in the journal Nature Neuroscience.
The researchers compared young people with participants aged 65 to 75. Using electroencephalography (EEG), they tracked slow brain waves during deep sleep, while positron emission tomography (PET) scans measured tau protein buildup.
Among older participants with higher levels of tau protein, the slow waves spread across smaller areas of the brain and occurred in isolation more often. The more disrupted this spread was, the worse participants were at retaining new information overnight, the researchers found.
What the follow-up showed
A number of the volunteers had their assessments repeated several years later. Rising tau protein levels were accompanied by further disruption to deep sleep and further memory decline. The researchers noted that these changes appeared even in people without a diagnosis of Alzheimer's disease.
Which comes first remains unclear
The study's authors said it is not yet possible to determine which develops first, tau protein buildup or sleep disruption. However, they said the results suggest that changes in deep sleep may accompany processes linked to Alzheimer's disease long before clear symptoms appear.
Alzheimer's disease is the most common cause of dementia, a progressive condition that gradually impairs memory, thinking and daily functioning. Tau is a protein that, in a healthy brain, helps stabilize the internal structure of nerve cells, but in Alzheimer's disease it forms abnormal tangles that are considered a hallmark of the disease alongside amyloid plaques.
The Berkeley team's findings add to earlier research cited in the report, which found that hormone replacement therapy reduced the risk of dementia and Alzheimer's disease in women.
