Why do sleep

These include the following:. Alexa Fry is a science writer with experience working for the National Cancer Institute. She also holds a certificate in technical writing. His research and clinical practice focuses on the entire myriad of sleep disorders.

A nighttime cough is the cold symptom most likely to interfere with sleep. Learn how to sleep with a cough…. Learn more about the causes and underlying mechanisms of REM rebound, a phenomenon in which a person temporarily experiences more….

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It is mandatory to procure user consent prior to running these cookies on your website. The Sleep Foundation editorial team is dedicated to providing content that meets the highest standards for accuracy and objectivity. Our editors and medical experts rigorously evaluate every article and guide to ensure the information is factual, up-to-date, and free of bias. Updated September 11, Written by Alexa Fry.

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Was this article helpful? Yes No. Berger, F. Sleep and Your Health. MedLine Plus. National Institutes of Health. Brain Basics: Understanding Sleep. National Institute of Neurological Disorders and Stroke. Are You Getting Enough Sleep?

Centers for Disease Control and Prevention. National Heart, Blood and Lung Institute. Sleep Deprivation and Deficiency.

Physiological Reviews, 93 2 , — Schwab, R. Overview of Sleep. Eugene, A. The Neuroprotective Aspects of Sleep. MEDTube Science, 3 1 , 35— Learn more about How Sleep Works. First, the inversion of the relationship between size and sleep time makes sense if we remember how sleep links to metabolism.

Sleep works to counteract damage caused by energy production, and sleep is also reactive to stimuli via the neural reorganisation needed to encode information processed from the environment. Moreover, the counteracting work of repair, and reactive work of reorganisation, each occur at rates that are themselves determined by metabolism.

Consequently, when an animal is larger, it suffers less damage to a fixed volume of tissue or cells. It therefore requires less energy and consequently less sleep time to accomplish the repair. Which brings us back to the brain: unlike most other organs and tissues such as the heart, it has long been observed that brain size varies non-linearly with body size across species and as babies grow. With these two insights, we did a back-of-the-envelope calculation to see if repair and reorganisation being reactionary to metabolic processes in the brain which scales more slowly than the whole body could explain the longstanding puzzle of how sleep times change — why big animals need less sleep than small ones, and why adults need less than babies.

B ecause of our past research, we were well positioned to develop the equations to express the role of metabolism in repair and reorganisation while asleep. Our new theory for sleep was an outgrowth of this: any damage we incurred while awake had to be balanced by the energy required to repair that damage during sleep.

We contextualised this insight by looking at both the brain and the body, in order to figure out what the scaling relationships revealed about which one played the dominant role in accounting for sleep. This allowed us to derive the fundamental equation that related sleep time to awake time. From there, it was simple algebraic manipulation to discover that the best way to express and test the new theory was to focus on how the ratio of total sleep time to total awake time changed with brain or body size.

This represented a significant departure, since prior research had focused only on either sleep time or awake time in absolute, not relative, terms. Moreover, our equations also demanded that in testing our theory, the proper space to plot data was logarithmic — a space in which the step from one to 10 is the same distance as from 10 to , or from to 1, To test our theory, we began by analysing the largest existing dataset of sleep times of adult mammals that ranged from mice to elephants.

When these data were plotted according to our theory, we were delighted to find that they scaled just as we predicted for the case that sleep is primarily for repair in the brain. Indeed, we had derived a mathematical formula for how long adult animals sleep. As a further test, we later wondered whether the theory would also apply to how sleep changes as individuals grow.

We all know that newborns and children sleep much longer than adults — but does that map on to the rates and magnitudes of changes we see across species? Does the decrease of sleep times during growth mirror the decrease of sleep times across mammals of increasing size?

After the theory was developed, new data appeared on total sleep times, REM sleep times, brain size, and other properties from human birth through adulthood, as interest in understanding sleep gained broader scientific and popular appeal. With great anticipation we and our collaborators plotted the new data — and were disappointed to find that the scaling of sleep times of children is substantially different from the results we had found across species. Our confusion grew when we observed further that the amount of REM sleep changes profoundly as we grow.

As a final surprise, we also found that brain metabolic rate and the rate of synapse formation the connections among neurons scaled radically differently than we expected. These findings reinforced our fascination with what a curious and biologically unusual process sleep is.

So, working with our collaborators Junyu Cao, Alex Herman and Gina Poe, who are experts in sleep and statistics, we returned to an alternative version of the theory, based on the idea that sleep was primarily for neural reorganisation to process incoming information from the day. From this perspective, sleep is still about the brain and its metabolic activity — much like in the repair theory for adult animals.

The big divergence that manifests during early childhood is because the way the brain grows in our early years is itself highly unusual compared with processes in the adult brain. In particular, synapse formation and brain metabolic rate increase incredibly fast in these early stages: a doubling in brain size results in a near quadrupling of synapse density and brain metabolic rate. Based on these insights, we extended our theory so that the primary function of sleep during early life is for neural reorganisation rather than just for repair.

Comparing our findings across species with those across growth led us to a final question. We were delighted with this stunning result. Second, we had discovered that these two states of sleep, while they looked remarkably similar from the outside, are actually analogous to completely different states of matter before and after the stark dividing line of 2. Before 2. After 2. Many questions still remain.

How much does sleep vary across humans and across species? Can this early fluid phase of sleep be extended? Is this phase already extended or shortened in some individuals, and what costs or benefits are associated with that? What other functions of sleep have piggybacked on to the primary functions of repair and neural reorganisation? How do the different reasons for sleep compete for or share sleep time, either across ages or even within a single night?

It will take much more work to fully unravel the mysteries of sleep, but our recent insights — about age-based shifts in the purpose of sleep and the mathematical, predictive theories that quantify them — represent an essential tool to plumb these depths even further.

Space exploration. Instead of treating Mars and the Moon as sites of conquest and settlement, we need a radical new ethics of space exploration. Ramin Skibba. Modern biomedicine sees the body as a closed mechanistic system. Another reason sleep is hard to understand is that the brain may be doing two different things during the two major stages of sleep. Non-REM sleep is marked by slow brain waves called theta and delta waves.

In contrast, the brain's electrical activity during REM sleep looks much like it does when a person is awake, but the muscles of the body are paralyzed. If you've ever experienced sleep paralysis , it's because you woke from REM sleep before this paralysis ended. Studies have found differences in the biology of the brain during these different stages. For example, during non-REM sleep, the body releases growth hormone, according to a review of the biology of sleep published by Frank in the journal Reviews in the Neurosciences.

Also during non-REM sleep, the synthesis of some brain proteins increases, and some genes involved in protein synthesis become more active, the review found. During REM sleep , in contrast, there does not appear to be any increase in this sort of protein-producing activity. One conclusion that has emerged from sleep research is that sleep does appear to be largely a brain-focused phenomenon, Frank said.

Although sleep deprivation affects the immune system and alters hormone levels in the body, its most consistent impacts across animals are in the brain. There is some evidence, in fact, that sleep is just something that neurons do when they're joined in a network. Even neuron networks grown in lab dishes show stages of activity and inactivity that sort of resemble waking and sleeping , Frank said. That could mean sleep arises naturally when single neurons begin to work together.

This could explain why even the simplest organisms show sleep-like behaviors. Even Caenorhabditis elegans , a tiny worm with only neurons, cycles through quiet, lethargic periods that look like sleep. Perhaps the first simple nervous systems to evolve exhibited these quiet periods, Frank said, and as brains got larger and more complex, the state of inactivity also had to get more complicated. But the idea that sleep is a natural property of neuron networks doesn't really explain what's going on during sleep.

On that front, scientists have a number of theories. One is that sleep restores the brain's energy, according to a review in the journal Sleep Medicine Reviews.