We all sleep for around a third of our time on the planet. While it might seem like a colossal waste of time to some people, sleep is pretty essential for many areas of health — particularly a healthy, functioning brain. There's a reason only one night's sleep deprivation makes your brain stop working: the organ requires deep, restful sleep to help repair itself, store data, remove waste, form memories, and many other functions. If you burn the midnight oil, experience insomnia, or just sleep poorly for a few nights, your brain's nightly routine is disrupted, and you'll feel it when you wake up.
Far from being relaxed when you're sleeping, your brain springs into a new phase of activity. "Our brains are very active during sleep and use a lot of energy," Dr. Mary Ellen Wells, Ph.D., the director of the University of North Carolina School of Medicine Neurodiagnostics and Sleep Science Program, tells Bustle. Only a small part of that energy is devoted to dreaming; the rest is spent on cleaning up, consolidating memories, and a host of other tasks. Experts believe this frenzy of activity happens during sleep because the brain can ignore the outside world, and just focus on itself. "While you're asleep, less data is coming in from your senses, allowing for other systems to function," sleep expert Dr. Michael Breus, Ph.D. tells Bustle.
One way to look at the brain's activities during sleep, Dr. Wells tells Bustle, is as clean-up. "Research suggests that our brain is doing very important housekeeping work during sleep, such as consolidating memories and sweeping out the neural trash," she says. Sleep is crucial for the process of forming new memories; if you don't sleep well, your brain doesn't transfer memories into long-term storage and you'll have difficulties recalling them later.
Dr. Breus tells Bustle that the brain also uses sleep as a chance to get rid of data it doesn't need, and to clear out physical waste products. "The brain removes protein and hormonal waste during sleep to keep its cells functioning," he says. A study published in 2019 found that cerebrospinal fluid, which circulates throughout the brain and spinal cord, increases in volume during sleep, possibly so that it can wash away rubbish that accumulated during waking hours. This removal process, Dr. Breus tells Bustle, operates on a circadian schedule; it's tied to when we sleep and wake up. The accumulation of these waste products is associated with neurodegenerative illnesses like Alzheimer's, so over time, sleep deprivation may impair your neural connections by clogging them with waste.
Besides cleaning, the brain also needs sleep to replenish itself. "Physical restoration of the brain occurs in stage three and four sleep," Dr. Breus tells Bustle. These are the deepest stages of sleep, when we experience rapid eye movement and dreaming. During this time, the brain goes to work on restoring any damage it's sustained from during the daytime. "Sleep is the state in which the brain restores the metabolic stores, trims unneeded synapses, reinforces specific connections and overall becomes more energy efficient," Dr. Bradley Vaughn M.D., director of the UNC Sleep Disorders Clinic and professor of neurology, tells Bustle.
Studies have shown that the brain's self-improvement overnight includes cutting back synapses to make room for new information and repairing damaged areas of cells. A study published in 2019 found that immune cells play a big part in this process; while we sleep, they get to work repairing nerve cells and the connections between them. Research published in Nature Communications in 2019 also suggested that the brain might be repairing damaged DNA in its neurons during the night. While we slumber, the brain is doing serious DIY — and when it's sleep-deprived, it can't repair itself and therefore can't function at peak efficiency.
All of these nighttime functions are designed to help the brain operate at 100% when you wake up in the morning. "Sleep helps your brain prepare for the work of being awake and helps you perform better," Dr. Vaughn says. While you snooze and have odd dreams about cheese, your brain is doing a full spring-clean — so make sure you try to get a good eight or nine hours, and give it a chance to flourish.
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Dr. Michael Breus Ph.D., sleep expert
Dr. Bradley Vaughn M.D., director of the UNC Sleep Disorders Clinic and professor of neurology
Dr. Mary Ellen Wells Ph.D., director of the UNC School of Medicine Neurodiagnostics and Sleep Science Program