Can you be awake and asleep at the same time? - Masako Tamaki

TED-Ed

18 May 202105:22

Summary

TLDRMany animals, including brainless jellyfish, need sleep, and some species like birds and marine mammals experience asymmetrical sleep, where one hemisphere of the brain is more active than the other. In extreme cases, such as with dolphins, this allows them to stay alert and keep breathing while resting. Birds like frigatebirds can even sleep mid-flight. Humans, too, experience a mild form of asymmetrical sleep, particularly in unfamiliar environments, like their first night in a new place, where one hemisphere stays more vigilant. This sleep behavior may enhance vigilance across species in potentially dangerous situations.

Takeaways

🐟 Even jellyfish, which lack brains, exhibit sleep-like states where they pulse less and respond more slowly to stimuli.
🦆 Many animals, including birds and mammals, experience asymmetrical sleep where one part of the brain sleeps while the other stays active.
🐬 Dolphins engage in unihemispheric sleep, where one hemisphere remains awake to allow them to swim and breathe without drowning.
🦭 Fur seals sleep unihemispherically while floating in the ocean, keeping one eye open to stay alert for predators from below.
🦅 Birds like mallard ducks and frigatebirds use unihemispheric sleep during migrations or while in vulnerable positions to stay alert to threats.
⏳ Frigatebirds, during long migrations, sleep in brief bursts, often while riding air currents, but get much less sleep than on land.
💤 Asymmetrical sleep's benefits vary by species; for some, full hemispheric sleep seems more restorative than unihemispheric sleep.
🔄 Dolphins can maintain high alertness for days by alternating which hemisphere sleeps, achieving deep sleep in each hemisphere.
🏨 Humans experience a subtle form of asymmetrical sleep, especially during the first night in a new place, leading to lighter sleep in one hemisphere.
👂 The 'first night effect' in humans involves the brain being more vigilant in unfamiliar environments, staying alert to potential threats.

Q & A

What is asymmetrical sleep and how does it differ from regular sleep?
-Asymmetrical sleep occurs when one hemisphere of the brain sleeps while the other remains more active. In contrast, regular sleep involves both hemispheres resting equally at the same time.
Which animals are known to experience unihemispheric sleep and why?
-Animals like bottlenose dolphins and fur seals experience unihemispheric sleep. Dolphins need to control their breathing consciously and must surface for air, so unihemispheric sleep allows them to stay awake enough to breathe and swim. Fur seals do this to remain alert to threats while migrating at sea.
How do mallard ducks use asymmetrical sleep for survival?
-Mallard ducks, especially those on the peripheries of a group, engage in asymmetrical sleep with one eye open and one hemisphere of their brain more active. This helps them stay alert to potential threats.
Why do dolphins need to sleep unihemispherically when they have a newborn calf?
-Dolphins need to swim nonstop for weeks after the birth of a calf to keep it safe. Unihemispheric sleep allows them to remain active and attentive to the calf’s needs while still getting rest.
How do birds like frigatebirds manage sleep during long migrations?
-Frigatebirds sleep in seconds-long bursts, sometimes using one or both hemispheres at a time. This occurs during midair migrations, often while riding air currents.
What is the 'first night effect' in humans, and how does it relate to asymmetrical sleep?
-The 'first night effect' is when humans sleep poorly in unfamiliar environments, such as the first night in a new place. During this time, one hemisphere experiences deeper sleep while the other remains more alert, a mild form of asymmetrical sleep.
How do dolphins maintain alertness for several days while sleeping unihemispherically?
-Dolphins alternate which hemisphere is awake, allowing them to get several hours of deep sleep in each hemisphere over a 24-hour period. This method helps them stay alert for long periods.
Why do fur seals prefer symmetrical sleep after being constantly stimulated?
-Fur seals showed a preference for sleep across both hemispheres after being constantly stimulated, suggesting that symmetrical sleep is more restorative for them than asymmetrical sleep.
What role does asymmetrical sleep play in human vigilance?
-Asymmetrical sleep helps humans remain vigilant in unfamiliar environments. The hemisphere in lighter sleep allows for a quicker response to potential threats, even if the environment is not dangerous.
Do animals benefit equally from asymmetrical sleep as they do from symmetrical sleep?
-It’s unclear if asymmetrical sleep provides the same benefits as symmetrical sleep. Some species, like fur seals, appear to need symmetrical sleep for full recovery, while dolphins can maintain high levels of alertness with unihemispheric sleep.

Outlines

00:00

🐬 Animals' Need for Sleep: Asymmetrical Sleep Across Species

Many animals, even those as simple as jellyfish, experience sleep or sleep-like states. However, sleep doesn't eliminate the need to be aware of threats, so many birds and mammals practice asymmetrical sleep, where one part of their brain sleeps while the other remains active. This phenomenon also occurs in humans. All vertebrate brains have two hemispheres, and typically, both show similar activity during sleep. But in asymmetrical sleep, one hemisphere can be in deep sleep while the other remains in a lighter state. In the most extreme form, called unihemispheric sleep, one hemisphere may appear completely awake while the other is in deep sleep.

🐋 Unihemispheric Sleep in Dolphins and Other Marine Mammals

Bottlenose dolphins exhibit unihemispheric sleep because their breathing is consciously controlled. If they don't surface for air, they could drown. When a calf is born, dolphins must swim continuously for weeks to protect it. This is possible because they sleep with one hemisphere at a time, allowing them to continue swimming and breathing while asleep. Other marine mammals like fur seals also rely on asymmetrical sleep, especially during long migrations. Fur seals sleep with one eye open while floating on the water to stay alert to potential threats.

🦆 Asymmetrical Sleep in Birds: Mallards and Migratory Flight

Birds also experience asymmetrical sleep, particularly in situations where vigilance is critical. Mallard ducks sleeping on the edge of a group use unihemispheric sleep, keeping one eye open and the corresponding hemisphere active. Some birds, such as frigatebirds, can even sleep mid-flight. Frigatebirds, during non-stop ocean crossings lasting up to 10 days, sleep in short bursts with one or both hemispheres at a time, while riding air currents. However, they sleep significantly less than when they are on land, highlighting their remarkable tolerance for sleep deprivation.

🦭 Sleep Recovery and Restoration: The Balance of Asymmetrical Sleep

Researchers are still studying how beneficial asymmetrical sleep is compared to bilateral sleep across species. Experiments with fur seals showed that while they can function using asymmetrical sleep, they prefer bilateral sleep when given the chance, suggesting it is more restorative. Dolphins, however, appear to function well using only unihemispheric sleep, remaining alert for at least five days while alternating deep sleep between hemispheres.

😴 Asymmetrical Sleep in Humans: The 'First Night Effect'

Humans also experience a subtle form of asymmetrical sleep. This is commonly seen in the 'first night effect,' where people sleep poorly in unfamiliar environments. Researchers found that during the first night, humans experience deeper sleep in one hemisphere (usually the right) while the other hemisphere remains more alert, particularly in response to unusual sounds. This vigilance, similar to that in animals, helps keep people more alert in unfamiliar or potentially unsafe environments, even though the threats are far less severe, like staying in a hotel room.

Mindmap

Keywords

💡Asymmetrical Sleep

Asymmetrical sleep refers to the phenomenon where different parts of the brain experience varying levels of sleep depth. One hemisphere can be in deep sleep while the other remains more active or alert. This is significant for animals like birds and marine mammals that need to remain vigilant to environmental threats or perform essential functions, such as breathing while sleeping.

💡Unihemispheric Sleep

Unihemispheric sleep is an extreme form of asymmetrical sleep where one hemisphere of the brain is in deep sleep while the other remains fully awake. This allows animals like dolphins to continue essential activities, such as swimming and breathing, while resting. It highlights how some species adapt their sleep to survival needs.

💡First Night Effect

The 'first night effect' describes the poor sleep quality people often experience on the first night in an unfamiliar place. This phenomenon is attributed to a mild form of asymmetrical sleep in humans, where one hemisphere remains more alert, potentially for increased vigilance in new environments. It mirrors the survival-based sleep patterns seen in animals.

💡Dolphins

Dolphins are highlighted in the script as an example of an animal that practices unihemispheric sleep. They need to maintain conscious control over their breathing and stay alert to surface for air, even while sleeping. This adaptation allows them to swim for extended periods and ensure the safety of their young.

💡Brain Hemispheres

The brain consists of two hemispheres: the right and left. In typical sleep, activity is similar across both hemispheres, but during asymmetrical sleep, one hemisphere can rest while the other remains active. This division of labor in the brain allows animals and humans to balance rest with the need for alertness.

💡Fur Seals

Fur seals are used as an example of marine mammals that utilize unihemispheric sleep. While migrating at sea, fur seals sleep with one brain hemisphere at a time, keeping an eye open and maintaining alertness to potential underwater threats. This adaptation helps them survive long periods of migration.

💡Mallard Ducks

Mallard ducks demonstrate how asymmetrical sleep is used in response to environmental pressures. Ducks sleeping on the periphery of a group practice unihemispheric sleep, keeping one eye open to monitor for threats. This behavior illustrates how sleep adaptations can enhance survival in birds.

💡Frigatebirds

Frigatebirds can sleep while flying during long migratory journeys. They enter brief bouts of sleep, sometimes using unihemispheric sleep, and take advantage of air currents to rest without stopping. This adaptation helps them handle sleep deprivation during non-stop transoceanic flights.

💡Sleep Deprivation

Sleep deprivation is referenced in the context of animals, like frigatebirds, who manage to survive on far less sleep during migration than they would on land. The script suggests that while they reduce their sleep drastically, they still manage to function, highlighting different species' varying tolerances for lack of sleep.

💡Vigilance

Vigilance refers to the heightened awareness some animals maintain even during sleep, particularly through asymmetrical sleep. This allows them to remain alert to potential threats or environmental changes, like the ducks and marine mammals that keep one eye open or one brain hemisphere active while sleeping.

Highlights

Many animals, including jellyfish, enter sleep-like states even without a brain.

Asymmetrical sleep occurs when parts of an animal's brain are asleep, while other parts remain active.

Unihemispheric sleep allows one hemisphere of the brain to remain awake while the other is in deep sleep.

Bottlenose dolphins sleep unihemispherically to maintain conscious breathing while swimming and caring for their young.

Fur seals engage in unihemispheric sleep during long migrations, keeping one eye open to remain alert.

Mallard ducks on the periphery of groups use unihemispheric sleep to stay vigilant with one eye open.

Frigatebirds sleep mid-flight, sometimes in bursts with one or both hemispheres asleep for short periods.

Frigatebirds sleep less than 8% of what they typically do on land during long migrations, showcasing high tolerance for sleep deprivation.

Asymmetrical sleep may not be as restorative as sleep across both hemispheres, based on fur seal recovery studies.

Dolphins can remain highly alert for at least five days by alternating which brain hemisphere is awake.

Humans may experience asymmetrical sleep, especially during the 'first night effect' in unfamiliar environments.

During the first night in a new place, the human brain experiences lighter sleep in the left hemisphere, possibly for vigilance.

Humans respond faster to sounds during lighter sleep in the left hemisphere on their first night in an unfamiliar setting.

In humans, asymmetrical sleep likely evolved to maintain alertness in unfamiliar environments, such as during travel.

The study of sleep in animals like dolphins and birds reveals how asymmetrical sleep allows for essential functions while maintaining vigilance.