Why is sleep so important? Your brain depends on it

URochester researchers have revealed that sleep does more than restore energy—it activates the brain’s waste-clearing system, protecting long-term brain health.

For as long as humans have been thinking about thinking, we’ve wondered why we sleep. From an evolutionary standpoint, it seems like a terrible idea: every night, we willingly surrender consciousness, mobility, and vigilance—leaving ourselves vulnerable to predators, accidents, and the elements. And yet sleep, which is essentially universal across the animal kingdom, is unavoidable.

At the University of Rochester, researchers have helped answer this ancient question. It turns out that sleep is not a passive state at all. Instead, it’s a critical time when the brain performs one of its most important jobs: cleaning itself.

A once-hidden network: the glymphatic system

In 2012, URochester neuroscientist Maiken Nedergaard and her colleagues discovered the glymphatic system, a previously unknown network that clears toxic waste from the brain. This system uses cerebrospinal fluid to flush away proteins such as beta-amyloid and tau—substances linked to Alzheimer’s and other neurodegenerative diseases.

Crucially, this cleaning process is most active during deep, non-REM (rapid eye movement) sleep. When we sleep, brain cells subtly shrink, creating space for fluid to flow more freely through brain tissue. The glymphatic system synchronizes brain waves, blood flow, and cerebrospinal fluid movement, turning sleep into a nightly maintenance cycle for brain health.

This discovery fundamentally changed how scientists understand why sleep is important. Sleep is not just downtime for the brain—it’s an active, essential biological process that supports memory, cognition, and long-term neurological resilience.

When sleep is disrupted, brain health suffers

The discovery of the glymphatic system has opened entirely new avenues of research for scientists across the globe. As a result, researchers have come to appreciate that not all sleep is created equal.

URochester researchers specifically have studied the role of disrupted sleep, circadian rhythms, aging, high blood pressure, and traumatic brain injury in affecting glymphatic function, reducing the brain’s ability to clear waste efficiently.

In laboratory studies, Nedergaard’s team found that the commonly prescribed sleep aid zolpidem (Ambien) suppressed glymphatic activity in mice, suggesting that some sedatives may interfere with the brain’s natural cleaning mechanisms. These findings highlight the importance of preserving healthy sleep architecture, not just logging enough hours in bed.

From fundamental discoveries to brand-new therapies

Building on these insights, URochester scientists are exploring how to restore or enhance glymphatic function. Collaborations with engineers at the University’s Hajim School of Engineering & Applied Sciences have demonstrated that stimulating lymphatic vessel contractions can revive age-related declines in brain fluid clearance—at least in animal models. Nedergaard also maintains a lab at the University of Copenhagen, connecting European scientists and collaborators with this research.

The question of why we sleep no longer belongs only to philosophers. At the University of Rochester, it has become a matter of biology, fluid dynamics, and brain health. With major federal funding and leading global partnerships, this research is opening new paths for treating and preventing neurological diseases, improving drug delivery to the brain, and designing sleep-based interventions that support lifelong brain health.

But for all its global reach and clinical promise, the impact of this research is ultimately intimate—and personal. Each night, when consciousness fades and the world recedes, our brains go to work—clearing waste, protecting themselves, and quietly preparing us for what comes next.