10 Amazing facts about sleep

We answer some curious questions about the way we sleep

1. Why do we toss and turn at night?

In some cases, the culprits are an uncomfortable bed or it being too hot or cold. You move around all night trying in vain to get comfortable. Other times, stress and anxiety prevent you from relaxing into deep sleep.

2. What is sleep paralysis?

Sleep paralysis is a common, terrifying condition where you wake up but can’t move and, in many cases, feel an evil presence in the room. Sleep researchers attribute it to a fluke state that is partially wakefulness and partially REM sleep, which keeps your body immobile and gives you dreamlike perceptions.

3. Why do we dream?

Dreaming occurs chiefly during REM sleep, when the cerebral cortex is buzzing with activity, apparently consolidating memories. One theory is that dreams are simply the cortex’s attempt to make sense of it all. Barraged with a stream of random activity, you do your best to piece it into some semblance of a story. Others don’t think it’s so random. One popular theory says dreams are practice for dealing with danger. The amygdalae – the seat of the fight-or-flight response – as well as brain areas associated with running and fighting are unusually active during REM sleep. We rehearse outrunning a lion so we have some experience if it were to happen. Another possibility is that dreaming is a way to work through problems, ideas and emotions without the constraints of logic. Interestingly, the activity of REM sleep is centred in the midline of the brain, associated with emotions. In contrast, there’s little activity in areas associated with logical thinking or recall of details.

4. Why do we have recurring dreams?

This may be like asking why we have recurring thoughts – there could be many reasons. Some theorise recurring dreams represent a problem you haven’t resolved, just like recurring daytime worries. But you might also dream about something simply because it’s important to you, in the same way you revisit pleasant memories.

5. Why do some people sleepwalk?

It’s a mysterious fluke, where a sleeper enters an odd arousal state during the deep stage NREM sleep. It’s more common among children than adults – 17 per cent of kids sleepwalk at some point – so it may be the result of incomplete nervous system development.

6. Why do we yawn when we’re tired?

The latest idea, supported by experimental evidence, is that yawning expands and contracts the maxillary sinus to pump air into the brain, acting as a built-in cooling system that prevents overheating. When you’re feeling tired, this system kicks in to help make your brain more alert.

7. Can eating cheese before bed give us nightmares?

A 2005 study from the British Cheese Board seemed to debunk this notion. Around three-quarters of cheese-eaters in the study reported sleeping very well, which the board secretary attributed to the soothing amino acid tryptophan prevalent in cheese. Interestingly, certain cheese varieties seemed to yield particular dreaming themes. Many Stilton-eaters reported especially vivid, off-the-wall dreams, for instance.

8. Why do we often jolt awake when close to sleep?

The jolt, known as the hypnic jerk, is a muscle spasm. The popular theory goes that your brain sometimes misinterprets the muscle relaxation of going to sleep as a falling sensation. To save you from a tumble, your brain triggers an abrupt ‘catch yourself’ reflex.

9. Why do so many people wake up grumpy from a deep sleep?

The sleep cycle is a steady, gradual transition between states. When it proceeds naturally, you move gracefully out of the deepest sleep level and through REM sleep before waking up. When you go directly from deep sleep to wakefulness, you can’t ease into consciousness. You’re highly disoriented, making you grumpy.

10. Is there any creature that doesn’t sleep?

Sleep manifests itself so differently across varied species that it’s hard to say. While researchers have identified sleep-like behaviour in animals as distantly related as fruit flies, they’re far from determining it’s a universal trait, and they can’t definitively say that any creature gets by 100 per cent sleep-free.

This article was originally published in How It Works issue 37, written by Tom Harris

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