Alzheimer's disease is associated with disrupted sleep and the accumulation of tau and proteins in the brain, which can emerge long before characteristic memory impairments appear. Two types of hippocampal sleep waves, slow oscillations and sleep spindles, are synced in young individuals, but have been shown to become uncoordinated in old age.

Matthew Walker, Joseph Winer, and colleagues at the University of California, Berkeley found a decrease in slow oscillations/sleep spindle synchronization was associated with higher tau, while reduced slow-wave-activity amplitude was associated with higher ?-amyloid levels.

The researchers also found that a decrease in sleep quantity throughout aging, from the 50s through 70s, was associated with higher levels of ?-amyloid and tau later in life. This means that changes in brain activity during sleep and sleep quantity during these time frames could serve as a warning sign for Alzheimer's disease, allowing for early preventive care.