Featured Research

from universities, journals, and other organizations

Why Sleep? Snoozing May Be Strategy To Increase Efficiency, Minimize Risk

Date:
August 23, 2009
Source:
University of California - Los Angeles
Summary:
A sleep researcher argues that sleep's primary function is to increase the efficiency of behavior when animals are awake by regulating behavior's timing and duration.

New research concludes that sleep's primary function is to increase animals' efficiency and minimize their risk by regulating the duration and timing of their behavior.
Credit: iStockphoto/Justin Horrocks

Bats, birds, box turtles, humans and many other animals share at least one thing in common: They sleep. Humans, in fact, spend roughly one-third of their lives asleep, but sleep researchers still don't know why.

According to the journal Science, the function of sleep is one of the 125 greatest unsolved mysteries in science. Theories range from brain "maintenance" — including memory consolidation and pruning — to reversing damage from oxidative stress suffered while awake, to promoting longevity. None of these theories are well established, and many are mutually exclusive.

Now, a new analysis by Jerome Siegel, UCLA professor of psychiatry and director of the Center for Sleep Research at the Semel Institute for Neuroscience and Human Behavior at UCLA and the Sepulveda Veterans Affairs Medical Center, has concluded that sleep's primary function is to increase animals' efficiency and minimize their risk by regulating the duration and timing of their behavior.

The research appears in the current online edition of the journal Nature Reviews Neuroscience.

"Sleep has normally been viewed as something negative for survival because sleeping animals may be vulnerable to predation and they can't perform the behaviors that ensure survival," Siegel said. These behaviors include eating, procreating, caring for family members, monitoring the environment for danger and scouting for prey.

"So it's been thought that sleep must serve some as-yet unidentified physiological or neural function that can't be accomplished when animals are awake," he said.

Siegel's lab conducted a new survey of the sleep times of a broad range of animals, examining everything from the platypus and the walrus to the echidna, a small, burrowing, egg-laying mammal covered in spines. The researchers concluded that sleep itself is highly adaptive, much like the inactive states seen in a wide range of species, starting with plants and simple microorganisms; these species have dormant states — as opposed to sleep — even though in many cases they do not have nervous systems. That challenges the idea that sleep is for the brain, said Siegel.

"We see sleep as lying on a continuum that ranges from these dormant states like torpor and hibernation, on to periods of continuous activity without any sleep, such as during migration, where birds can fly for days on end without stopping," he said.

Hibernation is one example of an activity that regulates behavior for survival. A small animal, Siegel noted, can't migrate to a warmer climate in winter. So it hibernates, effectively cutting its energy consumption and thus its need for food, remaining secure from predators by burrowing underground.

Sleep duration, then, is determined in each species by the time requirements of eating, the cost-benefit relations between activity and risk, migration needs, care of young, and other factors. However, unlike hibernation and torpor, Siegel said, sleep is rapidly reversible — that is, animals can wake up quickly, a unique mammalian adaptation that allows for a relatively quick response to sensory signals.

Humans fit into this analysis as well. What is most remarkable about sleep, according to Siegel, is not the unresponsiveness or vulnerability it creates but rather that ability to reduce body and brain metabolism while still allowing that high level of responsiveness to the environment.

"The often cited example is that of a parent arousing at a baby's whimper but sleeping through a thunderstorm," he said. "That dramatizes the ability of the sleeping human brain to continuously process sensory signals and trigger complete awakening to significant stimuli within a few hundred milliseconds."

In humans, the brain constitutes, on average, just 2 percent of total body weight but consumes 20 percent of the energy used during quiet waking, so these savings have considerable adaptive significance. Besides conserving energy, sleep invokes survival benefits for humans too — "for example," said Siegel, "a reduced risk of injury, reduced resource consumption and, from an evolutionary standpoint, reduced risk of detection by predators."

"This Darwinian perspective can explain age-related changes in human sleep patterns as well," he said. "We sleep more deeply when we are young, because we have a high metabolic rate that is greatly reduced during sleep, but also because there are people to protect us. Our sleep patterns change when we are older, though, because that metabolic rate reduces and we are now the ones doing the alerting and protecting from dangers."


Story Source:

The above story is based on materials provided by University of California - Los Angeles. Note: Materials may be edited for content and length.


Cite This Page:

University of California - Los Angeles. "Why Sleep? Snoozing May Be Strategy To Increase Efficiency, Minimize Risk." ScienceDaily. ScienceDaily, 23 August 2009. <www.sciencedaily.com/releases/2009/08/090820161333.htm>.
University of California - Los Angeles. (2009, August 23). Why Sleep? Snoozing May Be Strategy To Increase Efficiency, Minimize Risk. ScienceDaily. Retrieved September 30, 2014 from www.sciencedaily.com/releases/2009/08/090820161333.htm
University of California - Los Angeles. "Why Sleep? Snoozing May Be Strategy To Increase Efficiency, Minimize Risk." ScienceDaily. www.sciencedaily.com/releases/2009/08/090820161333.htm (accessed September 30, 2014).

Share This



More Health & Medicine News

Tuesday, September 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

How 'Yes Means Yes' Defines Sexual Assault

How 'Yes Means Yes' Defines Sexual Assault

Newsy (Sep. 29, 2014) Aimed at reducing sexual assaults on college campuses, California has adopted a new law changing the standard of consent for sexual activity. Video provided by Newsy
Powered by NewsLook.com
Scientists May Have Found An Early Sign Of Pancreatic Cancer

Scientists May Have Found An Early Sign Of Pancreatic Cancer

Newsy (Sep. 29, 2014) Researchers looked at 1,500 blood samples and determined people who developed pancreatic cancer had more branched chain amino acids. Video provided by Newsy
Powered by NewsLook.com
Colo. Doctors See Cluster of Enterovirus Cases

Colo. Doctors See Cluster of Enterovirus Cases

AP (Sep. 29, 2014) Doctors at the Children's Hospital of Colorado say they have treated over 4,000 children with serious respiratory illnesses since August. Nine of the patients have shown distinct neurological symptoms, including limb weakness. (Sept. 29) Video provided by AP
Powered by NewsLook.com
Dr.'s Unsure of Cause of Fast-Spreading Virus

Dr.'s Unsure of Cause of Fast-Spreading Virus

AP (Sep. 29, 2014) Doctors at the Children's Hospital of Colorado say they have treated over 4,000 children with serious respiratory illnesses since August. Nine of the patients have shown distinct neurological symptoms, including limb weakness. (Sept. 29) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins