The Link between Sleep and Alzheimer’s: it’s a Vicious Cycle

Jun 16, 2015 | alzheimers, sleep | 0 comments

A build-up of beta-amyloid on the brain, thought to be essential in the development of Alzheimer’s disease, can prevent deep sleep. This in turn leads to an impaired ability to expel this toxic protein.

Quality of sleep may be a crucial factor in the onset of Alzheimer’s disease, according to new research from neuroscientists at the University of California, Berkeley. This potentially hugely influential new study has found that excessive deposits of the beta-amyloid protein, believed to trigger Alzheimer’s, can prevent an individual from reaching a deep sleep, possibly resulting in memory decline.

The study, published in Nature Neuroscience, was overseen by three senior authors: neuroscientists Matthew Walker, Bryce Mander and William Jagust. Jagust said, “Over the past few years, the links between sleep, beta-amyloid, memory and Alzheimer’s disease have been growing stronger. Our study shows that this beta-amyloid deposition may lead to a vicious cycle in which sleep is further disturbed and memory impaired.”

The positive news is that sleep deprivation can be treated by things like exercise, behavioural therapy and electrical stimulation. “The discovery offers hope,” said Walker. “Sleep could be a novel therapeutic target for fighting back against memory impairment in older adults and even those with dementia.”

Mander added, “If we intervene to improve sleep, perhaps we can break that causal chain.”

The research was carried out on 26 adults between the ages of 65 and 81, each showing no existing symptoms of neurodegenerative diseases or sleep disorders. Each person received PET scans to measure levels of beta-amyloid on the brain, before being asked to memorise 120 word pairs and then being tested on some of them. The participants then had eight hours of sleep, with their brain waves measured by EEG, and upon waking their brains were scanned with fMRI as they attempted to recall the other word pairs. At this crucial point, scientists tracked activity in the hippocampus, the temporary storage zone for memories before they are transferred to the prefrontal cortex.

The general results were that those with high levels of beta-amyloid had the poorest quality of sleep, and thus performed badly on the memory test after sleeping. Indeed, some forgot half of the information they had memorised just a day before.

“The more beta-amyloid you have in certain parts of your brain, the less deep sleep you get and, consequently, the worse your memory,” said Walker. “Additionally, the less deep sleep you have, the less effective you are at clearing out this bad protein. It’s a vicious cycle.”

Matthew P Walker et al. β-amyloid disrupts human NREM slow waves and related hippocampus-dependent memory consolidation., Nature Neuroscience, June 2015 DOI: 10.1038/nn.4035