New research suggests that poor sleep may be a crucial missing piece in the Alzheimer's puzzle, and could lead to new treatments for the debilitating memory loss associated with the disease.
Scientists from the University of California, Berkeley in the US have found evidence that the protein believed to trigger Alzheimer's disease, known as beta-amyloid, may also be involved in blocking deep, restorative sleep - the kind that we need each night in order to move our short-term memories over to a more permanent region of our brains.
"Over the past few years, the links between sleep, beta-amyloid, memory, and Alzheimer's disease have been growing stronger," neuroscientist William Jagust, who was involved in the study, said in a press release. "Our study shows that this beta-amyloid deposition may lead to a vicious cycle in which sleep is further disturbed and memory impaired."
Beta-amyloid proteins are naturally found in healthy brains, but usually they're cleaned out each night during deep, non-rapid eye movement (non-REM) sleep. When they start to build up, it's associated with Alzheimer's disease as well as sleep disorders. But this is the first time a study has found a link between these two phenomena in human participants.
To find this link, the researchers looked at 26 adults aged between 65 and 81, who hadn't been diagnosed with dementia or any sleep disorders. All participants were given positron emission tomography (PET) scans to measure their beta-amyloid accumulation at the start of the trial. They were then asked to memorise 120 word pairs and were tested on how well they remembered them straight afterwards.
That night, the participants went into a closely monitored sleep for eight hours, and the next morning were tested on the 120 word pairs again, this time while having their brains scanned by an fMRI machine.
What the researchers found was that participants who had the highest levels of beta-amyloid in their medial frontal cortex had the worst night's sleep, and also performed the worst on the memory test the next day. This suggests that they hadn't spent long enough in non-REM sleep to lock away the new information they'd learnt.
"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 lead researcher Matthew Walker. "Additionally, the less deep sleep you have, the less effective you are at clearing out this bad protein. It's a vicious cycle."
"But we don't yet know which of these two factors - the bad sleep or the bad protein - initially begins this cycle. Which one is the finger that flicks the first domino, triggering the cascade?" he added.
The team has published their results in the journal Nature Neuroscience, and is now running a new research project in an attempt to find out whether poor sleep could be an early indicator of Alzheimer's.
The good news is, if lack of quality sleep really does contribute to Alzheimer's-related memory loss, it might be something we can prevent through exercise, behavioural therapy or even electrical stimulation.
"This 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."