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

Summary

Many 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.