Deep sleep may protect against Alzheimer’s memory loss

There are four main stages of sleep. The third stage of non-rapid eye movement (NREM) sleep is known as deep sleep or slow-wave sleep.

This is the stage of sleep when the body and brain are most at rest. The body’s heart and breathing rates slow and brain waves become longer and slower. Deep sleep is also the hardest stage to wake up from.

Sleep disorders including sleepwalking and bedwetting are most likely to occur during the deep sleep stage.

Deep sleep is the time when the body can repair tissue, bones, and muscle. It also helps to improve immune system function and metabolism and takes time to replenish the body’s energy stores.

Additionally, it is during deep sleep that the brain consolidates new memories.

Previous research shows deep sleep improves memory and helps maintain the learning efficiency of the brain.

“Sleep in young healthy adults, and deep sleep specifically, is known to boost memory performance,” Dr. Matthew Walker, professor of neuroscience and psychology and director of the Center for Human Sleep Science at the University of California, Berkeley, senior author of this study explained to Medical News Today.

“It does this in lots of different ways, some of which is that it helps during deep sleep to take those memories and you continue to replay those memories at night, the neural signature, as if you’re etching the memory trace more powerfully into the brain,” he explained.

“The other mechanism that we know of is that deep sleep actually transfers memories from a short-term vulnerable reservoir to a more permanent long-term storage site within the brain and (protects) them. And so that you come back the next day and by way of these mechanisms, you have hit the save button on those memories, and you don’t suffer as much forgetting,” he continued.

According to Dr. Walker, researchers have known for some time that Alzheimer’s disease is typified by memory decline.

“The two protein culprits that instigate Alzheimer’s disease — beta-amyloid and tau protein — we know are associated with memory decline. And the more that you have in the brain, the greater the memory impairment overall on average” , he explained.

“However, when you look at the data and you look at the relationship between how much beta-amyloid in the brain and how much memory impairment across a large number of individuals, there are some individuals who have high amounts of beta-amyloid and very impaired memory, but yet there are other individuals that have the very same amount of beta-amyloid, but their memory seems to be largely intact. How is that possible?” Dr. Walker continued.

Dr. Walker said that question led them to the theory of a cognitive reserve.

“Perhaps there are factors that help almost act like a supporting choir to a flagging lead vocalist brain, which is under the attack from Alzheimer’s protein, and they sort of offer this support to boost memory back up,” he said.

“In other words, they are a protective factor or a resilience factor, hence the term cognitive reserve factor, that they give you back some memory cognitive reserve that acts as a buffer to serve against the compression detriment of memory impairment,” he explained.

Dr. Walker said certain factors across a person’s lifespan, such as education and physical activity, can impact their cognitive reserve. However, those factors are not changeable as a person ages.

That led them to look at sleep as a potential cognitive reserve factor.

“If it is a missing cognitive reserve factor [it] is not just exciting because we would discover a new reserve factor, but it is something that is modifiable — we can now do something about it,” Dr. Walker said.

In this study, the research team recruited 62 older adults from the Berkeley Aging Cohort Study. All study participants were healthy and had not been diagnosed with dementia. Half of the participants had high levels of beta-amyloid deposits in their brains, while the other half did not.

Scientists monitored the sleep waves of study participants while they slept in a laboratory with an electroencephalography (EEG) machine. Once the participants woke up, they were asked to complete a memory task of matching names to faces.

Upon analysis, Dr. Walker and his team found study participants with higher amounts of beta-amyloid who had higher levels of deep sleep performed better on the memory test than those with the same amount of beta-amyloid who had worse sleep.

“What we found [i]s that deep sleep came to the rescue of memory. And in those people who had lots of beta-amyloid in the brain, the greater the amount of deep sleep that they had, the greater the cognitive reserve boost and the better their memory was,” Dr. Walker said.

“So deep sleep in that group [who had better memory] specifically was acting as a cognitive reserve factor. And it’s almost as though deep sleep is acting like a life raft and it’s keeping memory afloat and stopping it being dragged down by the pathology of Alzheimer’s disease beta-amyloid.”
— Dr. Matthew Walker

As for the next steps in this research, Dr. Walker said they now need to see if they can intervene and actually increase sleep in older adults, and actually demonstrate that it is a viable therapeutic target that can give back some degree of memory functioning.

“What we can say right now to doctors, is that many of them don’t speak about the prioritization of sleep, particularly in older adults. They just think, well, older adults don’t sleep well and that’s just part of aging — it’s not. Older adults need just the same sleep that we do in midlife — it’s just that the brain can’t produce it or is not as well able to produce it,” he said.

He said there are some options to help increase sleep quality, including good sleep hygiene, cognitive behavioral therapy for insomnia, and even electrical brain stimulation technology.

Dr. Walker suggested doctors talk to older adults about their sleep and its quality.

“And then thinking with the patient through the doctor how to improve their sleep — perhaps non-pharmacologically because that may not necessarily be the ideal approach — and see if we can use good sleep in midlife and early later adulthood as a preventative tool,” he added.

Dr. David Merrill, an adult and geriatric psychiatrist and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center in Santa Monica, California, who was not involved in the study, told Medical News Today this is an interesting study providing evidence that there is a genuine brain effect of our sleep.

“There’s a brain effect of sleep that we can improve through working on our sleep,” he said.

How to get deep sleep

“The things we do matter in terms of improving our physical health and our brain health. Doing things like having a regular bedtime, having a cool, dark environment for sleep, making sure we avoid screen time late in the day, and also avoiding caffeine after lunch. We can also do things like take a warm shower at night to try to boost our deep sleep.”
— Dr. David Merrill

“And the study is showing that these changes that we make that can improve deep sleep, may in fact help our memory performance in the day, even if we’re facing significant brain pathology from Alzheimer’s process in older adults,” Dr. Merrill said.

“It’s truly remarkable bridging the gap between the basic science and motivating behavior change,” he added.

Medical News Today also spoke with Dr. Clifford Segil, a neurologist at Providence Saint John’s Health Center in Santa Monica, California, about this study.

Dr. Segil, who was not involved in this study, commented he was concerned that people reading this study may mistakenly conclude a sleeping pill that causes them to sleep better is going to treat their memory loss or Alzheimer’s disease.

“This study said if you sleep more, your cognitive issues may be improved, which is fascinating and interesting, but very hard to prove,” he said.

“I would love to see the study repeated with a group of research patients given the medications which increase slow-wave sleep, to see if these results persist and continue to show patients with the high amyloid-beta burden who had increased slow-wave sweep had any improvement in their cognitive testing,” Dr. Segil said.

“I’d love them to repeat this test with those medications and see if the results are repeatable,” he added.