Press Releases & Research Commentary

Deep sleep allows the brain to wash away waste and toxic proteins more efficiently, according to a new mouse study published in the journal Science Advances. The new findings shed light on previous evidence linking Alzheimer's disease with aging and sleep deprivation.

"Sleep is critical to the function of the brain's waste removal system and this study shows that the deeper the sleep, the better," said Maiken Nedergaard, MD, DMSc, co-director of the Center for Translational Neuromedicine at the University of Rochester Medical Center (URMC) and lead author of the study.

"These findings also add to the increasingly clear evidence that quality of sleep or sleep deprivation can predict the onset of Alzheimer's and dementia."

The study suggests that the slow and steady brain and cardiopulmonary activity linked to deep non-REM sleep are optimal for the function of the glymphatic system, the brain's waste removal system. The findings may also explain why some forms of anesthesia can result in cognitive dysfunction in older adults.

New research shows how the depth of sleep can impact our brain's ability to efficiently wash away waste and toxic proteins. Because sleep often becomes increasingly lighter and more disrupted as we become older, the study reinforces and potentially explains the links between aging, sleep deprivation, and heightened risk for Alzheimer's disease.

"Sleep is critical to the function of the brain's waste removal system and this study shows that the deeper the sleep the better," said Maiken Nedergaard, M.D., D.M.Sc., co-director of the Center for Translational Neuromedicineat the University of Rochester Medical Center (URMC) and lead author of the study. "These findings also add to the increasingly clear evidence that quality of sleep or sleep deprivation can predict the onset of Alzheimer's and dementia."

The study, which appears in the journal Science Advances, indicates that the slow and steady brain and cardiopulmonary activity associated with deep non-REM sleep are optimal for the function of the glymphatic system, the brain's unique process of removing waste. The findings may also explain why some forms of anesthesia can lead to cognitive impairment in older adults.

The brain's system for removing waste is driven primarily by the pulsations of adjoining arteries, University of Rochester neuroscientists and mechanical engineers report in a new study. They also show that changes in the pulsations caused by high blood pressure slow the removal of waste, reducing its efficiency.

This might explain the association between high blood pressure and Alzheimer' disease, the researchers say. Alzheimer's, the most common cause of dementia among older adults, is characterized by abnormal clumps and tangled bundles of fibers in the brain.

The study, reported in Nature Communications, builds upon groundbreaking discoveries about the brain's waste removal system by Maiken Nedergaard, co-director of the University's Center for Translational Neuromedicine. Nedergaard and her colleagues were the first to describe how cerebrospinal fluid is pumped into brain tissue and flushes away waste. Subsequent research by her team has shown that this glymphatic waste removal system is more active while we sleep and can be damaged by stroke and trauma.

This latest research shows "in much greater depth and much greater precision than before" how the glymphatic system functions in the perivascular spaces that surround arteries in the outer brain membrane, says Douglas Kelley, an assistant professor of mechanical engineering and an expert in fluid dynamics. His lab is collaborating with Nedergaard's team as part of a $3.2 million National Institute on Aging grant.

For this study, Humberto Mestre, a PhD student in Nedergaard's lab, injected minute particles in the cerebrospinal fluid of mice, and then used two-photon microscopy to create videos showing the particles as they moved through the perivascular spaces.

What really happens when you sleep? You may be taking a break from consciousness when you snooze, but not all of your neurons are resting, Veasey says. While you rest, your brain solidifies the synapses involved in the important memories you want to keep (like the name of your new dentist) while pruning the synapses involved in less important memories (such as where you put your keys two nights ago).

Sleep also gives your brain a chance to clear out debris that accumulated during the day. In 2014, a team of scientists led by Maiken Nedergaard at the University of Rochester Medical Center published research suggesting that the brain rids itself of metabolic waste through a kind of plumbing system that works mainly while we sleep. Just as the lymphatic system clears unwanted waste from the rest of the body, what's called the glymphatic system eliminates debris and toxins from the brain and the central nervous system. Skimp on sleep, and this janitorial service can't keep up, so the rubbish starts to accumulate in your noggin.