The Miracle and Mystery of Sleep: 12 Remarkable Psychological Studies

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“Sleeping is no mean art: for its sake one must stay awake all day.” ~Friedrich Nietzsche

What beautiful rewards sleep delivers– if you can get enough of it.

Sleep has profound effects on our memories, desires, self-control, learning, relationships and more.

Here are twelve studies which demonstrate some of the psychological benefits of sleep and a few of the dangers of not getting enough.

1. Placebo sleep

Sleep is slippery beast, not least in how it’s susceptible to our perceptions of its quality.

If we think we’ve had a wonderful sleep last night, we feel and perform better, even if our sleep was actually the same as usual.

This is what Draganich and Erdal (2014) found in a study which had participants hooked up to sensors which they were told were measuring the quality of their sleep.

Actually the sensors weren’t measuring anything. Instead the researchers randomly told some people they’d had better sleep than others.

When they were given a cognitive test the next day, those who’d been told they slept the best also did the best in the test.

Their self-reported sleep quality had little effect on the test results.

The researchers dubbed this ‘placebo sleep’.

2. Emotional sleep

During sleep our memories are reorganised and made stronger–in particular the emotional centres of the brain are highly active.

Psychologists have found that the mind is cataloguing our memories and deciding what to keep and what to throw away.

Sleep expert Elizabeth A. Kensinger explains:

“Sleep is making memories stronger. It also seems to be doing something which I think is so much more interesting, and that is reorganizing and restructuring memories.”

A review of studies on sleep found that we tend to hold on to the most emotional parts of our memories (Kensinger & Payne, 2010).

3. Blame bad sleep on the full moon

If your sleep wasn’t up to scratch last night, perhaps it was partly down to the phase of the moon.

People often complain of worse sleep around the full moon, but until recently scientists have been sceptical.

A study by Cajochen et al., 2013, though…

“…studied 33 volunteers in two age groups in the lab while they slept. Their brain patterns were monitored while sleeping, along with eye movements and hormone secretions.”

This is what they found:

“The data show that around the full moon, brain activity related to deep sleep dropped by 30 percent. People also took five minutes longer to fall asleep, and they slept for twenty minutes less time overall.

The researchers think it may be because we have a kind of ‘moon clock’ inside us that tracks its cycles and affects our hormone levels. This is in addition to the better known circadian rhythms which affect many bodily processes during the day.

→ Read on: Bad Night’s Sleep? Blame the Full Moon

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4. Junk food cravings

One of the dangers of not getting enough sleep is craving junk food.

Recent research from UC Berkeley scanned the brains of 24 participants after both a good and a bad night’s sleep (Greer et al., 2013).

After disturbed sleep, there was increased activity in the depths of the brain, areas which are generally associated with rewards and automatic behaviour.

It seems a lack of sleep robs people of their self-control and so their good intentions are quickly forgotten.

Hence those junk food cravings get out of control.

→ Read on: Why the Sleep-Deprived Crave Junk Food and Buy Higher Calorie Foods

5. Learn in your sleep

It’s not possible to learn something new when you sleep, like a foreign language, but you can reinforce something you already know.

Gobel et al. (2012) found that students learned to play a series of musical notes better after listening to them during a 90-minute nap.

One of the authors, Paul Reber explained:

“The critical difference is that our research shows that memory is strengthened for something you’ve already learned. Rather than learning something new in your sleep, we’re talking about enhancing an existing memory by re-activating information recently acquired.”

→ Read on: Offline Learning: How The Mind Learns During Sleep

6. Benefits of a six-minute nap

Even tiny amounts of sleep can be beneficial.

A study by Lahl (2008) found that even a short six-minute nap was enough to measurably improve performance on a test of word recall.

Tell that to the boss the next time your caught ‘resting your eyes’ at work!

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7. Night owls have lower integrity white matter

Different neural structures have been discovered between people who are night owls and early risers.

Research on 59 participants, those who were confirmed night owls (preferring late to bed and late to rise) had lower integrity of the white matter in various areas of the brain (Rosenberg et al., 2014).

Lower integrity in these areas has been linked to depression and cognitive instability.

Unfortunately work, school and other institutions mostly require early rising, which, for night owls, causes problems.

As night owls find it difficult to get to sleep early, they tend to carry large amounts of sleep debt.

In other words, they’re exhausted all the time and their brains clearly show the consequences.

→ Read on: Like to Stay Up Late? Different Neural Structures Found in the Brains of Night Owls

8. Children’s sleep

Children are processing way more information than adults because everything is so new to them.

That is why irregular bedtimes at a young age can reduce their cognitive performance.

One study had children learning a task which had a hidden pattern. After a night’s sleep they were much more likely to guess the secret pattern without being told (Wilhelm et al., 2013).

Children also outperformed adults, suggesting that sleep was more important to them for this task.

9. Adolescents need more sleep

Adolescents typically require an hour or two more sleep than adults.

If so, why do we make them get up so early for school?

One study has delayed the waking up time of adolescents at a boarding school by just 25 minutes (Boergers et al., 2013).

They found that afterwards the number of students getting more than 8 hours sleep a night jumped from 18% to 44%.

On top of this, the students experienced less daytime sleepiness, were less depressed, and found themselves using less caffeine.

→ Read on: Later School Start Times Improve Sleep and Daytime Functioning in Adolescents

10. Consolidate motor skills

When we are learning a motor skill, like playing the piano, our brains continue to process the information after we’ve finished.

In research by Allen (2012), musicians who practised a new song had improved in speed and accuracy compared with before a night’s sleep.

Like memory, a good night’s sleep can also improve motor performance.

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11. Relationship damage

People are usually at their worst after a bad night’s sleep, but what does that do to their intimate relationships?

A new study finds that even one bad night’s sleep can be surprisingly damaging to a relationship (Gordon & Chen, 2013).

They found that even for those who were good sleepers, just a single night’s poor sleep was associated with increased relationship conflict the next day.

→ Read on: How Just One Night’s Poor Sleep Can Hurt a Relationship

12. Hidden caves open up during sleep

If sleep has such amazing restorative powers then what is going on physiologically?

New research has discovered “hidden caves” inside the brain, which open up during sleep, allowing cerebrospinal fluid (CSF) to flush out potential neurotoxins, like β-amyloid, which has been associated with Alzheimer’s disease (Xie et al., 2013).

The flushing out of toxins by the CSF may be central to sleep’s wondrous powers.

→ Read on: Hidden Caves in the Brain Open Up During Sleep to Wash Away Toxins

Last word

Last word to the playwright Wilson Mizner who said:

“The amount of sleep required by the average person is five minutes more.”

Quite right.

→ Related: 10 Sleep Deprivation Effects.

Image credits: Ryan Ritchie & HaoJan Chang & Simon Pais-Thomas & Sheldon Wood

About the author


Dr Jeremy Dean is a psychologist and the author of PsyBlog. His latest book is "Making Habits, Breaking Habits: How to Make Changes That Stick". You can follow PsyBlog by email, by RSS feed, on Twitter and Google+.

Published: 3 February 2014

Text: © All rights reserved.

Images: Creative Commons License