Deep Sleep May Help Protect Against Alzheimer’s Disease and Cognitive Decline

If anyone knows how powerful sleep can be, it’s a new parent. Omer Sharon, a neuroscientist currently raising a newborn while conducting postdoctoral research at the University of California, Berkeley, dreamily told Being Patient that good sleep is like magic. 

“You wake up after a nap, after a night of good sleep, and you feel that everything is better,” he said.

In 2021 Sharon began working with Matthew Walker, a neuroscientist who describes himself as a “sleep diplomat.” Together, they are trying to understand how the structure of a person’s sleep changes during Alzheimer’s disease.

Deep sleep gets shallower during Alzheimer’s disease progression

As a graduate student, Sharon worked in a sleep lab in Tel Aviv, Israel. He and his team invited older adults – some of whom had previously been diagnosed with either amnestic mild cognitive impairment (aMCI), which is a decline in primarily in memory, or Alzheimer’s disease – to take a cognitive test and then spend the night with electrodes on their heads to record their brainwaves.

Sleep is a cycle: over the course of a night, a person’s brain repeats a series of distinct phases including one called “slow wave” or “deep sleep.” Scientists are still trying to understand exactly what this phase does, but one of the leading theories is that the big, slow waves of electrical activity that scientists can record during this stage reflect some sort of rinse cycle that clears out junk like amyloid plaques.

“You want them to be as big as possible and spread,” Sharon said of the cleansing waves.

However, when Sharon and his graduate school team looked at the data from their study participants, they found that the bottoms of the electrical waves didn’t dip down as low in the brains of people with aMCI. For people with Alzheimer’s, the bottoms of the waves were even shallower.

Furthermore, these slow waves spread through less of the brain in people with aMCI and even less of the brain in people with Alzheimer’s.

When Sharon’s team pooled the data for all of the participants, they found that wave depth and spread did a fairly good job of predicting a person’s performance on the cognitive test, regardless of whether or not that person had a diagnosis of aMCI or Alzheimer’s.

Now, Sharon is working with Walker at UC Berkeley to expand on these findings. In a study Sharon expects to be published soon, the neuroscientists collected data from American adults and compared the location and amount of tau in their brains to the size and shape of their slow waves during deep sleep. It turned out that slow wave electrical activity became particularly impaired when pathological tau tangles spread to the front of the brain, where slow waves originate.

This does not establish a clear cause-and-effect relationship between changes in sleep quality and the molecular changes that drive Alzheimer’s disease progression. Rather, to Sharon, it most likely reflects a negative feedback loop between declining sleep quality and neurodegeneration. Poor sleep may prevent the brain from cleaning out pathological proteins, which could then accumulate making it harder for the brain to complete high quality sleep cycles.

“You have this vicious cycle of something going wrong, and then additional things go wrong down the line,” he said.

Breaking the vicious cycle

Zsofia Zavecz, a neuroscientist at the University of Surrey after completing her PhD in Walker’s Berkeley lab, said she understands why sleep scientists often frame declining sleep quality and Alzheimer’s disease progression as a vicious cycle.

“But I prefer not to,” she told Being Patient, “because I think the good news about this is we can break the cycle by improving sleep.”

Zavecz describes good quality deep sleep as a cognitive reserve factor, compensating for the accumulation of the amyloid plaques and tau tangles that drive Alzheimer’s disease. Other factors that might offer cognitive reserve include spending more years in school, engaging in mentally engaging work, and getting regular exercise. Over the course of a person’s life, these factors can lower a person’s risk of developing dementia.

While Zavecz was working with Walker, she led a study to see if deep sleep quality could explain, in part, why one person who has accumulated enough amyloid to be considered amyloid positive may have cognitive impairment and another may have no symptoms at all.

Indeed, when they focused on people who were amyloid positive, Zavecz and her team found an association between the quality of a person’s deep sleep during the night and their performance on a memory test the next day.

Even as Sharon continues to find evidence that pathological Alzheimer’s proteins are associated with worsening sleep quality, Zavecz’s study shows that people can still get good quality sleep as these proteins start to accumulate. Thus, deep sleep is a cognitive reserve factor that people can cultivate even at an older age.

For people looking for tips on how to sleep better, Zavecz recommended getting plenty of exercise during the day and practicing good sleep hygiene around bedtime. She also said it’s a good idea to go to sleep and wake up at regular times so that your brain is not constantly adjusting its sleep cycle schedule.

But at the end of the day, both Sharon and Zavecz said that no one should let the quality of their sleep become a source of stress, because stress makes it harder to sleep.

Andrew Saintsing (@AndrewSaintsing) earned a PhD in biology, and now he writes about science for outlets like Drug Discovery News.