SCIENCE14 - How Animals Sleep

I often see birds doing their high-energy thing in trees outside my home office windows, and have wondered about what they do at night.  Do they “sleep?”  I did a little research, and turned up some fascinating (to me) information about how birds sleep.  My curiosity led me to a quick check on sleep habits of other animals, found similarly fascinating info, and decided to research and write this blog on “How Animals Sleep.”


 

I will start with an introduction to sleep in animals, then discuss why animals sleep, why animals sleep differently, typical animal sleep patterns, and when animals sleep.  Next, I’ll explore how different animal groups sleep, including mammals, reptiles, birds, fish, amphibians, and invertebrates - with examples of different animal behaviors in each group.  Finally, I’ll discuss what researchers think about potential animal dreaming and sleep disorders. 

My principal sources include “Sleep in animals,” Wikipedia.org; “A Guide to How Animals Sleep,” sleepopolis.com; “How Do Animals Sleep,” sleepfoundation.org; “How Do Animals Sleep?”, school.sleepeducation.com; “How Do Different Animals Sleep?”, mattressclarity.com; “Do bugs sleep?”, Everything about insects catching Zs,” reliantpest.com; “How Much Do Animals Sleep?”, faculty.washington.edu; plus, numerous other online sources.

Introduction

Sleep is common to all living beings, from fruit flies to blue whales.  Sleep is a state of altered consciousness that recurs on a 24-hour cycle known as the circadian rhythm.  Though it was once believed to be a passive state, sleep involves complex physiological changes that allow for learning, memory processing, and essential processes such as healing and food metabolism.  Even one-celled organisms, which don’t sleep in the traditional sense, display evidence of a circadian rhythm.  Though all animals share the need to sleep, how they sleep varies widely across species. 

Note:  Besides decades of observations, sleep in humans and other animals is typically studied under controlled conditions using an electroencephalogram (EEG), which measures electrical activity in the brain.  The miniaturization of animal-borne wireless EEG loggers has recently made it possible to record sleep in wild animals, in its full ecological context. 

Why Animals Sleep

Studies prove that insufficient sleep has significant health effects such as reduced cognitive function, lowered immunity, increased risk of disease, and death.  Sleep may also serve to protect some species of animals from predators and other dangers by keeping them inactive during the night when they’re more vulnerable.

Other functions of sleep may include:

  • Helping the brain restructure and reorganize, particularly after injury
  • Improving the strength and speed of synapses between neurons
  • Restoring the capacity to learn
  • Increasing long-term memory

 

In addition to visual signs such as lying down, or finding a protected place to perch, sleep in animals is recognizable by closing of the eyes in those with eyelids, and distinct patterns of lowered-arousal brain waves.

Why Animals Sleep Differently

The way animals sleep depends on their size, what they eat, and their unique physiology.  In general, small animals sleep more than large animals, though they may sleep for only a few minutes at a time.  Whales and elephants require very little sleep.

Sleep and Metabolism.  Small animals like mice have fast metabolisms, meaning their bodies use energy  quickly.  These smaller animals need to sleep multiple times in a 24-hour period, restoring energy, and may even fall asleep while eating or engaged in other activities.  This may explain in part why larger animals sleep less than those that are very small.  Some researchers theorize that evolution may favor animals of a larger size by allowing them to consolidate sleep into one longer session.

Sleep, Body Size, and Diet.  Another hypothesis about animals and sleep is that larger animals need to eat more to sustain their superior muscle mass.  Many very large animals are non-carnivores, and take in relatively few calories in comparison to meat-eaters.  Large animals who subsist on grasses and leaves spend less time sleeping than carnivores, and more time foraging for food.  Large non-carnivore animals that don’t require much sleep include giraffes, elephants, and horses.

Sleep and Predators.  Smaller animals may be more at risk from predators, making the ability to sleep in shorter snatches of time essential to survival.  Being awake, vigilant, and ready to move is important for prey animals, while sleep makes them vulnerable.  Sleeping in underground burrows and other hidden areas can also make sleep less dangerous.

Animals like horses, cows, elephants, and giraffes have adapted to sleep standing up in order to protect themselves from dangerous predators.  Since they’re already standing up, it’s much easier for them to run away and make their escape.  These animals are able to lock their legs so that the muscles don’t need to keep them in place.  When they sleep standing up, they cannot achieve REM sleep (see below), which is why they will lie down on some occasions.

Larger animals have less to fear from natural predators, and can sleep for more consolidated periods of time with less fear.  Consolidated sleep allows larger animals to spend less time in transitional states between waking and sleeping, and more time in productive activities such as hunting or mating.

Sleep and Immunity.  Scientists have found an association between longer, more consolidated periods of sleep, and environments with a greater risk of infection.  Because sleep helps to boost immunity, animals who are exposed to more pathogens may have evolved to sleep in consolidated blocks of time so that energy could be directed to the immune system.

Studies show that rabbits who sleep for longer periods of time after infection recover more quickly.  Higher densities of disease-fighting white blood cells appear to have evolved along with longer periods of sleep, further bolstering the hypothesis that sleep serves a protective function against parasites, viruses, and bacteria.

Typical Animal Sleep Patterns

Sleep Phases.  Sleep in animals can take place all at once, in two phases, or more than two phases.  

Sleeping in one consolidated block of time, known as monophasic sleep, is common in human beings but less common in other species.  Monophasic sleep typically lasts between six and nine hours.  Less than 14% of animals have sleep patterns that can be considered monophasic.

Monophasic animals include primates such as the marmoset species of monkey.  Marmosets sleep in trees and live in groups of stable families, making them less vulnerable to predators.  This may explain why these animals adapted to monophasic sleep, unlike many other species of primates.

Biphasic sleep refers to a longer sleep session lasting five to six hours, plus a nap or siesta.  The nap can be brief or last a few hours.  Another form of biphasic sleep is called segmented sleep.  This refers to two segments of sleep interrupted by an hour or two of wakefulness.

Note:  Monophasic sleep was not the norm for human beings until the Industrial Revolution, the extension of labor hours, and invention of the electric light.  Before that, biphasic sleep was common across cultures worldwide.  Human sleep patterns followed two cycles (biphasic) every night.  Each block of sleep would be around four hours, with most people staying awake for two to four hours in between.

Polyphasic sleep describes sleep that takes place in shorter sessions throughout the day and night.  Most animals, including cats, dogs, and birds, are polyphasic sleepers, and sleep in four to six segments per day.

 

Animal sleep phases over the 24-hour day.


REM Sleep.  In humans, the period of sleep in which most dreams occur is called REM (rapid eye movement) sleep.  During REM sleep, a person’s brain activity, breathing, heart rate, and blood pressure increase, and the eyes move rapidly while closed.  REM sleep is thought to play an important role in memory and learning.  During normal sleep, a person goes through four to five sleep cycles that last about 90 minutes each, and include both REM sleep and non-REM sleep.

All mammals studied thus far, and several other animal groups, exhibit signs of REM sleep, suggesting that they dream, just like humans do.  (See below)

Half-Brain Sleep.  Unihemispheric sleep is a type of sleep during which one half of the brain remains awake while the other half sleeps.  The eye corresponding to the sleeping half of the brain closes, while the eye that corresponds to the awake half stays open.

Animals who exhibit “half-brain” sleep include dolphins, some species of birds, and seals.  Half-brain sleep allows these animals to maintain vital behaviors and respond to predators, while getting the benefits of sleep.

Hibernation.  Some warm-blooded animals hibernate during the winter to escape cold temperatures and conserve energy when sufficient food is not available. 

A hibernating animal may not move, eat, or sleep for several months.  Hibernation is a state of torpor (physical or mental inactivity), and is characterized by reduced metabolism, heart rate, and breathing.  These vital bodily functions decrease during sleep, as well, but the changes are much more significant during hibernation.

Cold-blooded animals can enter a hibernation-like state called brumation, a period of dormancy that occurs during cold weather.  For brumation, the animal will find an insulated place to stay during a particularly cold time of year.  

A hibernation-like state during hot weather is called estivation.

These reduced activity states allow for the conservation of energy during times of extreme temperatures and food scarcity.

 

Animals that hibernate.
 

Bottom of FormWhen Animals Sleep

Animals evolved to be active during the day, night, or at dawn and/or dusk.  The part of the day when animals sleep depends on their environment, feeding habits, and vulnerability to predators.  Types of activity behavior include the following:

Diurnal animals are active during the day and sleep at night.  Diurnal animals include human beings, most primates, and many species of birds, including ostriches.

Nocturnal animals are active and feed at night.  Nocturnal animals include raccoons, bats, wolves, skunks, and jaguars.

Crepuscular animals are most active at dawn and dusk, and include bears, deer, and housecats.  Crepuscular animals can also be active on cloudy days and bright nights.  Crepuscular activity is likely an adaptation to the behavior of predators, who tend to be most active at night or in full daylight.

The sleep of metaturnal animals is not diurnal, nocturnal, or crepuscular, and is distinguished by sporadic activity at all times of day.  Examples of metaturnal animals include lions, some primates, mice, and rabbits.  Some animals such as lemurs are considered metaturnal because they switch from diurnal to nocturnal with the seasons.

How Mammals Sleep

Mammals are warm-blooded vertebrates who nurse their young and have hair or fur.  Despite differences in size and physiology, mammals sleep very similarly to humans.  Their sleep is divided into non-REM, slow wave sleep, and REM sleep, although the amount of sleep varies greatly.  Mammals born in a more fully developed state such as horses experience more non-REM sleep than animals who are less developed, like cats and human beings.  This supports the theory that REM sleep and dreaming are essential to growth and development in young animals.

Mammals sleep to save their energy and restore mental and physical energy. The amount of sleep mammals need depends on several factors, including age, body size, environment, diet, and the safety of its sleep site.  Whether a mammal lives on land or in the sea can also affect how much sleep it needs

Land Mammals.  Even within land mammals, the amount of sleep required varies from species to species.  For the most part, giraffes tend to sleep during the night, although they do get in some quick naps throughout the day.  Giraffes can sleep standing up as well as lying down, and their sleep cycles are quite short, lasting 35 minutes or shorter.  Tall giraffes twist around when they lie down to achieve REM sleep.  The giraffe curves its long neck around like a pretzel.  Then it rests its head on its backside or on the ground.

Giraffes must lie down to achieve REM sleep.

 

Elephants, like giraffes, likely only sleep for a few hours each day due to their massive body size and need to graze often.  Scientists can tell elephants are sleeping when their trunks stop moving.  Elephants usually sleep standing up, or they may lean against a termite mound or large tree.  If an elephant sleeps on its side to achieve REM sleep, it only sleeps for a short period, usually a half-hour or less, to keep its body weight from crushing its internal organs.  Predation risk may also play a role in how little they sleep, given how far they’ll travel while awake.  Scientists have observed elephants traveling for nearly two days without sleeping at all.

Like giraffes and elephants, horses don’t sleep much, and when they do, they can sleep standing up.  However, once they enter REM sleep, they lie down.

Note:  Because REM sleep causes muscle paralysis to prevent the acting out of dreams, most land mammals must lie down during this stage of sleep, even if it lasts for only a few minutes. 

On the other end of the spectrum, nocturnal brown bats spend most of the day sleeping.  Lions, rats, cats, monkeys, rabbits, dogs, and chimpanzee spend about half the day sleeping.  

Average hours of sleep per day for land mammals – most to least.

No.

Animal

Average Hours of Sleep per Day

1

Bat

19.9

2

Tiger

15.8

3

Squirrel

14.9

4

Lion

13.5

5

Rat

12.6

6

Cat

12.1

7

Rhesus Monkey

11.8

8

Rabbit

11.4

9

Dog

10.6

10

Chimpanzee

9.7

11

Pig

7.8

12

Goat

5.3

13

Cow

3.9

14

Sheep

3.8

15

Horse

2.9

16

African Elephant

2.0

17

Giraffe

1.9

 

Most mammals sleep several times per day (polyphasic sleep).  Depending on the animal, they may sleep more during the day or night, although diurnal animals typically tend to sleep at night.

Primates sleep in one period (monophasic) each day.  Monkeys sleep sitting upright to stay safe against predators, but great apes like gorillas and chimpanzees prefer to lay down.  They sleep on nesting platforms in trees, very similar to human beds.  These platforms allow them to stay up high in trees so they can stay safe from predators and annoying insects.  These comfortable platforms give the apes a feeling of security, allowing them to get more REM sleep. 

Some land animals, like leopards, have excellent balance, and can sleep on a tree limb without falling off.  The three-toed sloth also sleeps on a tree limb.  It tends to sleep in a sitting position, using a tree branch for back support.

Like some humans who share a bed with a partner, herd animals like cows and sheep, sleep closely together since there’s much more safety in numbers against potential predators.

Marine Mammals.  When it comes to sleep duration, walruses are like the bats of the sea, sleeping most of the day.  They can sleep in water and on land, although they sleep for longer periods on land.  When walruses sleep in the water, they usually lie at the bottom, float along the surface, or lean against something while in a standing position. They can even hook their tusks onto an ice floe and sleep that way.  Like elephants, walruses can go for days without sleep.

Other marine mammals sleep far less than walruses.

Average hours of sleep per day for marine mammals - most to least.

No.

Animal

Average Hours of Sleep per Day

1

Walrus

19.4 - 20.5

2

Sea Otter

11

3

Bottle-nosed Dolphin

10.4

4

Polar Bear

7 - 8

5

Gray Seal

6.2

6

Sperm Whale

1.7


Note:  Polar bears are classified as marine mammals because they spend most of their lives on the sea ice of the Arctic Ocean, depending on the ocean for their food and habitat; polar bears are the only bear species to be considered marine mammals.

Most marine mammals live in the water, but they come to the surface to breathe. To keep from suffocating while they sleep, animals like eared seals, dolphins, many whales, and manatees experience half-brain sleep; the other hemisphere is awake, so the animal can move, see through one eye, breathe, and enjoy the restorative benefits of sleep while still being on the lookout for potential threats.

In some case, dolphins may float on top of the water while they sleep.  This behavior is called “logging,” and scientists have even discovered that some dolphins sleep while swimming in a circle.  Another study found that dolphins may be able to achieve a level of half-brain sleep that still allows them to perform complex tasks.

Bottle-nose dolphins sleeping on the surface of the water.

 

Sea otters float on the surface of the water while sleeping.  They often wrap themselves in kelp, a type of seaweed.  The kelp prevents them from drifting away while they sleep.

Sperm whales sleep upright.  Scientists believe these whales may require the least amount of sleep of all mammals.

Newborn orca whales can go weeks without sleep.  So can their mothers. 

While their overall sleeping time remains the same, during summer, polar bears will usually sleep more during the day time as opposed to the night.  Polar bears will usually only sleep continuously for about one hour at a time.

When it’s time for sleep, polar bears will dig a shallow pit or shelter den in the snow.  Polar bears also have been known to sleep out in the open on sea ice or a flat surface.

Male polar bears do not hibernate; pregnant females, enter into a state of hibernation.  They do so from about October or November through March or April. The female polar bear's heart rate slows to about 27 beats per minute from a normal resting heart rate of about 46 beats per minute.  The female’s temperature does not decrease, this ensures the cubs will stay warm.

How Reptiles Sleep

Reptiles are cold-blooded vertebrates that have dry skin covered with scales or bony plates and usually lay soft-shelled eggs.  Reptiles comprise lizards, snakes, crocodiles, and turtles.

Researchers once believed that reptiles slept very differently from other animals due to the structure of their brains.  But recent studies have found that reptiles display similar sleep patterns to human beings and other mammals.  These patterns include slow wave sleep and REM sleep, suggesting that reptiles dream to process and store memories. 

Other research shows possible evolutionary connections between the way reptiles rest and bask in warmth, and the sleep of mammals.  In fact, all waking and sleeping states in mammals might have come from reptiles, who evolved much earlier than mammals and birds. 

The starkest difference in the sleep patterns of reptiles and mammals may lie in the length of their sleep cycles.  A reptilian sleep cycle lasts only 80 seconds compared with mammalian cycles, which typically last 90 minutes.  Reptiles go through around 350 sleep cycles per night, while humans experience around four to five.  Though the sleep cycle is significantly shorter, the proportion of REM sleep to non-REM remains the same in reptiles as it does in human beings and other animals.

Some reptiles, like snakes and lizards, don’t have eyelids to close when they sleep.  Instead, they have a protective scale called a brille that slides across their eyes. The brille is transparent or only slightly opaque, making it appear as if these animals sleep with their eyes open.

Sleeping snake, wrapped around a tree.  Note the protective scale covering its eye.

 

Most reptiles sleep around 16 to 17 hours a day, and may go into a state of brumation (reduced activity and metabolism) in response to colder temperatures and less available food.  

Like other animals, lizards choose sleep perches that maximize their safety. They may sleep on leaves, with their heads oriented towards the path a predator would use to approach them.  

Snakes may sleep for days at a time, digesting their food.

Predator crocodiles, exhibit half-brain sleep so they can keep an eye out for threats and food.

Aquatic turtles may spend hours sleeping on a dry dock or with their head poking out of the water, but they may also sleep underwater for shorter periods of time, coming up to take a breath when necessary. Land turtles don't swim like aquatic turtles so they can sleep anytime, anywhere.

How Birds Sleep

Birds are warm-blooded vertebrates that evolved from dinosaurs, which evolved from early reptiles.  Birds experience both REM and non-REM sleep, and, depending on the type of bird, may be diurnal, nocturnal, metaturnal, or crepuscular.  Like reptiles, the sleep cycles of birds are much shorter than those of human beings.  They may spend only eight seconds in REM sleep before shifting to slow wave sleep.

Birds sleep an average of 10 to 12 hours at night, but it could vary because they sleep more in winter and less in summer.  That's because they don't need to use much energy during the cold winter season.

Some birds perch on the edge of a branch or other object to rest, whereas others sleep on the ground, hidden among leaves, or at the water’s edge.  Birds are able to remain perched while asleep because their body weight causes the tendons in their feet to lock, preventing them from falling.  Some birds such as the flamingo can even sleep while balancing on only one leg!

Sleeping owl perched on tree limb during daytime. Even though most birds sleep with one eye open, owls sleep with both eyes closed.

 

Unihemispheric sleep allows birds to protect themselves from predators.  For example, mallard ducks can sleep in a row.  The ducks at the end will be most likely to sleep with half their brain, with their outward eye remaining open, while ducks in the middle sleep with both eyes closed.

Birds can sleep while flying during long migrations by utilizing their capacity for half-brain sleep.  Some types of birds, such as the alpine swift, can fly for seven months at a time without landing.  They are able to drink, eat, and sleep while in flight, and rest by both sleeping and gliding with minimal flapping of their wings.

However, migrating birds do sleep significantly less while migrating.  White-crowned sparrows, for instance, only get a third of the sleep they do when they’re not migrating.  They’ll catch up on sleep with daytime micro-naps, and during times when they’re perched. 

Though many animals exhibit signs of sleep deprivation, like engaging in longer and deeper periods of sleep after extended activity, alpine swifts are able to completely recover from activity by sleeping in flight.  This suggests that some birds are able to perform all physiological functions while in flight, including resting and sleeping.

How Fish Sleep

Fish are limbless cold-blooded vertebrate animals with gills and fins, and live wholly in water.

Brain patterns of certain types of sleeping fish are similar to land animals, raising the possibility that sleep functions developed in the brain before fish and land animals took different evolutionary paths.  Studies show that, like reptiles, mammals, and birds, fish experience slow wave sleep and REM sleep.

Most fish species will sleep for a period of 8 to 12 hours, depending on their size and species characteristics. 

Fish have no eyelids and are unable to close their eyes.  Like other animals, when fish sleep their vital signs such as heartbeat and breathing decrease.  They remain still and relaxed, their tails drop, and they don’t react to stimuli.  The movements of their mouths and gills can decrease by half.  Some fish simply float when they sleep, while others hide in rocks, nests, or coral.  Parrotfish even secrete a cocoon of mucus around themselves to stay protected while they sleep.

Fish can’t close their eyes when sleeping because they have no eyelids.

 

Some fish are able to go without sleep when constant activity is required, such as during spawning season or while fanning eggs to keep them oxygenated.  Fish may also forego sleep during migration.  Once these periods of high activity are over, the fish return to their normal sleep patterns, and can display symptoms of sleep deprivation (see below) until they “catch up” on sleep.

Some types of sharks need to stay in continual motion to keep water flowing across their gills and providing a steady supply of oxygen.  A shark’s spinal column regulates its movements as it swims, which may allow the brain to sleep while the body stays in motion.  Scientists also hypothesize that these sharks may take advantage of currents, allowing the current to push water over their gills and enable respiration. It is more likely, however, that they employ half-brain sleep, enabling one eye to stay open and monitor their environment.

Other types of sharks breathe through their cheeks, which allows them to rest motionless in a cave or on the sea bottom.   Scientists have observed nurse sharks, entering a sleep-like state in which they appear sluggish and still. Their pectoral and tail fins prop them up as they use a rock for a pillow.

How Amphibians Sleep

Amphibians are cold-blooded, vertebrate animals that have an aquatic phase of life (spent in water, breathing through gills) and a terrestrial phase of life (living on land, breathing with lungs).  The primary amphibian animals are frogs and salamanders.

On land, adult frogs and salamanders are most active at night and “sleep” during the day.  During the winter, they burrow underground to enter a state of brumation, where they stop moving and eating for months.

Amphibians do not sleep like humans or other mammals.  During the day, they exhibit non-REM resting states.  Although resting, they can quickly respond to external stimuli (food, predator).   

No studies have scientifically observed how long amphibians rest; from a behavioral standpoint it is believed that amphibians spend 12 - 16 hours a day resting.

During warmer months, tree frogs generally rest in trees, aquatic frogs in water, and terrestrial frogs underground.   Salamanders rest in shady cracks in the rock, underground, or in other dark, damp places.

Tree frog “resting” in a tree.

 

Amphibians can also enter a state of torpor to survive in arid climates. This state is known as estivation, where similar to brumation, amphibians burrow deep underground and remain inactive for months.

How Invertebrates Sleep

An invertebrate is a cold-blooded animal with no backbone.  Invertebrates can live on land - like insects, spiders, and worms - or in water, such as crabs, lobsters, octopuses, clams, and coral.

Sleep has been described in crayfish, characterized by passivity and increased thresholds for sensory stimuli as well as changes in the EEG pattern, markedly differing from the patterns found in crayfish when they are awake. 

Sleep-like states have been described in jumping spiders, too, as well as regularly occurring bouts of retinal movements that suggest a REM sleep-like state.  Also, sleeping cuttlefish and octopuses show signs of having REM-sleep behaviors.

Many species of insects have brains that require sleep to function.  Rest is necessary for insects to remain alert during their waking hours.   The more sleep an insect gets, the longer it lives (which is why queen ants outlive their overworked subjects).  Increased alertness helps insects avoid predators and search for food with better precision.

Bees have some of the most complex sleep states among insects.  It has been shown that they use sleep to store long-term memories.  Honeybees sleep between five and eight hours per day.

Honey bees sleep to restore energy and store long-term memories.
 

How long an insect’s sleep cycle last depends on its species, as well as whether it’s a “queen” or “worker.”  For instance, a “queen” fire ant gets around nine hours of continuous sleep, while her workers take short naps, adding up to just five hours. Meanwhile, fruit flies take shorter naps for just over 2.5 hours.  Butterflies, moths, and other insects experience torpor, and may remain dormant for the entire winter season. 

Some insects need to catch up on their sleep after they’ve been deprived.  However, some insects like bees don’t require a rebound but will instead sleep deeper for shorter periods.

One study involving fruit flies showed that lack of sleep impaired their performance and vigilance.  Another showed that honeybees kept awake all night were less effective at communicating directions to fellow bees. 

Extreme sleep deprivation causes cellular damage in insects like fruit flies, eventually killing them if left untreated.  See below.

Unicellular organisms do not necessarily "sleep", although many of them have pronounced circadian rhythms. The fresh-water polyp Hydra vulgaris and the jellyfish Cassiopeia are among the most primitive organisms in which sleep-like states have been observed.  Observing sleep states in jellyfish provides evidence that sleep states do not require that an animal have a brain or central nervous system.

Animal Dreaming

Researchers believe it’s likely that animals who experience REM sleep also dream.  REM sleep is associated with processing and storing memories, and may be essential to learning and survival.  Studies on human beings show that REM sleep is also important for processing emotions, and can reduce negative emotions and reactivity.  REM sleep may serve a similar function in more emotionally developed animals, such as dogs, primates, and dolphins.

Studies reveal that rats and human beings share similar brain activity during sleep.  Neurons in the brains of rats rewarded with food will fire in a distinctive pattern.  This pattern will replay during rest, suggesting the formation of memories.

Research conducted on cats demonstrated that, without the muscle paralysis characteristic of REM sleep, cats go through motions suggestive of dreaming, including stalking prey and pouncing.  REM sleep appears to have a crucial survival function, allowing animals of all species to discard unnecessary memories, store important ones, and use past experiences to better adapt to their environments.

Animal Sleep Disorders

Animals exposed to a stressful environment can display the symptoms of insomnia.  Studies show that insomnia in animals, like human beings, may occur for the following reasons:

  • Disruption of the circadian rhythm
  • Activation of the central nervous system, including wake-promoting regions of the brain
  • Release of stress hormones
  • Disturbance of the stable regulation of sleep, or the sleep drive

 

When exposed to stressful conditions, animals seem to have difficulty sleeping just as human insomniacs do.  Studies on animals are generally conducted in laboratories, zoos, and other unnatural environments, making it difficult to determine why insomnia may occur in certain species.

Fruit flies bred in the laboratory can suffer from the symptoms of insomnia, including difficulty falling asleep and staying asleep.  It’s unknown if flies not specifically bred for research purposes would suffer from insomnia in their natural environment.

Zebrafish with a particular mutant gene will experience insomnia, sleeping 30% less than fish of the same species without the gene.  Overexpression of a gene called NMU, also found in mammals, appears to be the cause of the behavior.   Studies of these fish, who have similar sleep patterns to human beings, may help lead to better insomnia treatments and more effective sleep medications.

Some animals can die if they are subject to sleep deprivation for long enough. This is true for mammals like rats, and some insects may also die due to prolonged periods of sleep deprivation.  It’s very difficult to discern whether other animals suffer from the same cognitive impairment that humans do whenever we lose sleep.  It’s also difficult to tell if this problem shows itself in the form of sleepiness or fatigue like in humans.

Domestic animals can suffer from other sleep disorders common in human beings, such as bedwetting and sleepwalking.  Further studies are needed to determine whether these disorders occur in animals in the wild.  Dogs, cats, and horses may also display symptoms of narcolepsy, an autoimmune disease characterized by excessive sleepiness and sudden “sleep attacks.  Muscle weakness is another common feature of the disorder. Narcolepsy in animals can be caused by a genetic mutation or occur without an apparent cause.

 

I really enjoyed putting this blog together.  Took a lot of work and energy.     Time for some Z’s

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