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.
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. |
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.
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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