Category: Sleep

Four 10 to 15 minute sleep interruptions in the night enough to leave people groggy and grumpy.

A full night’s sleep which is interrupted can be as bad as getting only half a night, finds a new study taking a novel approach to sleep problems.

Despite how common it is for parents of young children to be awakened many times during the night, the effects have never been systematically investigated.

Parents are not the only ones who suffer, explains Prof. Avi Sadeh, who led the new research:

“Doctors on call, who may receive several phone calls a night, also experience disruptions.

These night wakings could be relatively short — only five to ten minutes — but they disrupt the natural sleep rhythm.

The impact of such night wakings on an individual’s daytime alertness, mood, and cognitive abilities had never been studied.

Our study is the first to demonstrate seriously deleterious cognitive and emotional effects.”

In their study participants were awakened four times during a normal 8-hour night (Kahn et al., 2014).

Each time they had to complete a computer task that took 10-15 minutes before they went back to bed.

In the morning they took tests of alertness, attention and mood. These were compared with results from two other nights when they’d had either:

• An uninterrupted 8 hours.
• An artificially restricted 4 hours.

The effects on mood, attention and alertness for the interrupted 8 hours were as drastic as only getting 4 hours sleep.

In comparison to the uninterrupted 8 hours, people felt more depressed, fatigued, confused and lower in vigour.

And this was the effect of just one interrupted night.

These deleterious effects can snowball, as Sadeh explained:

“Our study shows the impact of only one disrupted night.

But we know that these effects accumulate and therefore the functional price new parents — who awaken three to ten times a night for months on end — pay for common infant sleep disturbance is enormous.

Besides the physical effects of interrupted sleep, parents often develop feelings of anger toward their infants and then feel guilty about these negative feelings.”

Image credit: Simon Pais-Thomas

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, which is generally associated with rewards and automatic behaviour.

The frontal lobes, just behind and above the eyes, which help provide self-control, were less active.

The finding may help explain why the sleep-deprived are more likely to give in to calorific temptations.

One of the study’s authors, Matthew Walker, explained:

“”What we have discovered is that high-level brain regions required for complex judgments and decisions become blunted by a lack of sleep, while more primal brain structures that control motivation and desire are amplified.”

In other words: lack of sleep robs people of their self-control and so their good intentions are quickly forgotten.

On top of this, the researchers found that after being deprived of sleep, participants displayed greater craving for high-calorie junk food. The more sleep-deprived they were, the greater the cravings.

By contrast, when they were well rested, the same people were better able to resist temptation.

Bring me burgers!

This study is the latest in a wave of recent research examining the link between lack of sleep and poor dietary choices.

• A study of 13,284 teenagers found that those who slept poorly also made poor decisions about food.
• Similarly, a Swedish study found that at a buffet, tired people were more likely to load up their plates (Hogenkamp et al., 2013).

The link has even been made from poor sleep through to food shopping.

A Swedish study found that men who were sleep-deprived bought, on average, 9% more calories than those who’d had a good night’s sleep (Chapman et al., 2013). These results were likely the result of the poor decision-making identified by the UC Berkeley study.

It had been thought that the tendency to eat more after poor sleep was related to the so-called ‘hunger hormone’ ghrelin. But the latest studies suggest that it’s simple self-control that is most important in causing the sleep-deprived to over-indulge.

Dr Lauren Hale, author of the study of teenagers, said:

“If we determine that there is a causal link between chronic sleep and poor dietary choices, then we need to start thinking about how to more actively incorporate sleep hygiene education into obesity prevention and health promotion interventions.”

To find out more about sleep hygiene, check out: How To Fall Asleep Fast.

Also here are 10 sleep deprivation effects.

Image credit: Josh Janssen

It’s been more than a century since the first scientific evidence was produced that sleep benefits memory.

But the man who stumbled on it, German psychologist Hermann Ebbinghaus, couldn’t believe that learning during sleep could explain anomalies in his results, and he rejected the possibility.

It wasn’t until forty years later that the power of ‘the sleep effect’ was demonstrated directly (Jenkins & Dallenbach, 1924).

Since then, studies have been carried out to find out what types of memory are affected by sleep, how much sleep is required and how the effect occurs.

For example, people have asked: is it just memory for facts, or does it also work for physical movements?

The interest in the effect is hardly surprising: the idea that you can learn while unconscious is one more beautiful thing about sleep.

Learn while you sleep

Here’s a recent example of a typical study investigating the effect.

Payne et al (2012) had people learn a series of word-pairs, like RIDER and SWITCH, either at 9am in the morning or 9pm at night.

There were then tested at 30 minutes after learning, 12 hours later and 24 hours later.

The results showed that whether they learned in the morning or evening, it made little difference to their recall just 30 minutes later.

But, over a longer delay, differences did emerge.

The people who had learned the word-pairs before bed performed better than those that had learned them in the morning.

These are not isolated results. Fenn and Hambrick (2012) carried out a similar study and got the same result: people who learned before they slept did better than those who followed the learning with a period of wakefulness.

These researchers also found that some people, those with a better ‘working memory’, were particularly good at learning while they slept.

Six-minute benefit

There is now all sorts of research showing that different types of learning are improved by a subsequent period of sleep.

For example, procedural learning–like that involved in playing tennis or learning fingering on the piano–is improved by subsequent periods of sleep.

Similarly, perceptual learning–like being able to distinguish two notes from each other–has also shown improvements from subsequent periods of sleep.

Researchers then wondered how short the sleep can be to see the benefits.

It turns out that you’re better off to learn new information before your full eight hours. But benefits to learning have been shown in one study for a nap as short as six minutes (Lahl, 2008).

Learning offline

Scientists aren’t exactly sure why learning benefits from sleep. The old theory used to be that everyday events interfered with newly learned memories causing them to fade away or get muddled. In other words, sleep was better after learning because no new memories could interfere.

Now, though, many psychologists believe that there is an active process at work while we sleep.

During the unconscious period, our minds may be working on the memories and more strongly encoding them for later retrieval.

This may be part of the reason why, like many others, John Steinbeck pointed out:

“It is a common experience that a problem difficult at night is resolved in the morning after the committee of sleep has worked on it.”

Image credit: Toni Blay

“Legend has it that an observant goatherd named Kaldi discovered coffee in Ethiopia somewhere between about 300 and 800 A.D. He noticed that his goats did not sleep at night after eating coffee berries. He took the berries to a local abbot, who brewed the first batch of coffee, noting its effects on arousal and cognition.” (Smith et al, 2004)

Ever since then humans have been fascinated with caffeine, and rightly so.

Some of its effects are strange and contradictory. In many ways caffeine’s effect on your mind is much more about what you expect than what it actually does.

Hopefully you’ll find at least one or two things here to surprise you…

1. Caffeine doesn’t stop most people sleeping

The goatherd Kaldi may have been right about his goats, but not necessarily about humans. Despite all the fuss made about caffeine and sleeping, there’s little evidence that it’s a problem.

The research finds that the vast majority of people have worked out how to use it. It’s not that complicated: don’t have a double espresso at midnight. Duh.

Even then, there are studies where they give people caffeine secretly before they go to bed. Surprise, surprise it doesn’t generally affect their sleep that much!

2. People blame caffeine for anything and everything

It’s not just poor sleep, because people think caffeine is at least a bit bad for them, they blame all kinds of non-specific problems on it: headaches, bad night’s sleep, feeling jittery, and so on.

Researchers sometimes give people placebos and tell them they’ve had caffeine. People subsequently claim to have slept badly, developed headaches and all the rest.

But it can’t be due to caffeine, because they haven’t had any. So it must be down to what we expect caffeine to do to us.

3. Coffee plus nap?

It might seem mad to have a cup of coffee and then go for a nap. But if you’re sleep deprived, this may be the answer.

Studies have tried giving tired people 200mg of caffeine (a cup or two of instant coffee), then telling them to take a nap.

The caffeine plus the nap often has an additive effect on performance. In other words the caffeine improves performance above the nap on its own.

Try it: have a coffee and a nap of around 5-15 minutes and see you feel. Even people who don’t normally nap can find this beneficial.

4. Boosts in sustained attention

Most people feel more alert after a coffee, but are they any sharper when scientifically tested?

The answer is: in some ways yes, but in many ways not.

The strongest positive finding is that caffeine increases sustained attention and vigilance. This is the kind of attention you need to keep doing a relatively routine task that is unchallenging. That’s why it’s often so good at work: it keeps us plodding on through boring stuff that we’ve got to get through.

This finding is particularly strong for people who haven’t had enough sleep, which is most of us nowadays.

When we stray away into other psychological areas like reaction times, learning and memory, things become much less clear. Sometimes caffeine improves them, sometimes it makes them worse and sometimes there’s no difference.

In general, though, there’s little evidence that caffeine makes much difference on tasks that require pure thought.

5. Two cups good, five cups bad

Like everything in life, you can have too much of a good thing. And caffeine is no different.

In the studies mentioned above, when people have around 200-300mg of caffeine, they get the benefits mentioned. That’s around three espressos or 2-3 cups of instant coffee.

Upwards of 500 mg, though, and there’s no increase in performance and people start to experience negative effects.

Naturally, though, this will depend on your usual level of intake; as the body and mind gets used to caffeine, like any drug.

6. No withdrawal symptoms when giving up?

If you fancy giving up caffeine then prepare for withdrawal symptoms between 12 and 24 hours after your last cup of coffee. Then you may start to develop a headache and feel irritable, tired and anxious.

Or will you?

Even withdrawal symptoms may be at least partly down to our expectations about the effects of caffeine. It’s little studied, but there’s a suggestion that if you don’t expect to get withdrawal effects, then you won’t actually get them.

That’s probably why some people report having no withdrawal symptoms when they give up caffeine. So giving up may not be as hard as you think.

7. Feeling good

No caffeine drinker needs me to tell them that some coffee makes them feel better and too much makes them feel bad.

Moderate doses are the key. What counts as a moderate dose will depend on your usual intake and your genetic susceptibility, which is inheritable. So if your parents can take a triple espresso without their heads exploding, then you probably can as well.

But even an inherited sensitivity to caffeine can be overcome with real dedication to the cause.

8. Coffee kills pain

There is some suggestion in the research that caffeine can help reduce pain.

If you’ve got a tension headache, for example, then studies suggest that acetaminophen (paracetamol) plus caffeine will provide better pain relief than acetaminophen alone.

Rather than causing non-migraine headaches, caffeine has been shown in one study to cure them!

9. Caffeine sharpens the senses

Caffeine ramps up the senses a little in all sorts of interesting ways. Here are a few:

• Studies find that after a cup of coffee or two people can actually see better in the dark. The boost is between 20 and 38%.
• People can discriminate between colours better when they’ve had some caffeine.
• Caffeine helps people ignore distracting stimuli in the environment.

10. Caffeine probably isn’t addictive

Technically caffeine is not really addictive because of the way it works in the brain and because many people don’t suffer withdrawal symptoms when they give up.

However a small number of people do look like they’re addicted to it. But when you compare caffeine to the drugs that are really addictive, like cocaine or heroin, it’s pretty clear that caffeine is not properly addictive.

Image credit: Eric

But now there’s scientific evidence for a link between the moon’s cycle and human sleeping patterns. It comes from a new study published in Current Biology from researchers at the University of Basel:

“…[they] 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.” (Cajochen et al., 2013)

Vitally, the participants slept in tightly controlled conditions with no access to the current time. They could not see the moon from where they slept and they did not know what the study was about.

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. Study participants felt as though their sleep was poorer when the moon was full, and they showed diminished levels of melatonin, a hormone known to regulate sleep and wake cycles.”

Summing up the research, Professor Christian Cajochen said:

“The lunar cycle seems to influence human sleep, even when one does not ‘see’ the moon and is not aware of the actual moon phase.”

The fact that this study does find a connection—despite chiming with the popular imagination—is something of a surprise to scientists.

Many previous studies have failed to detect associations between the moon’s phase and human behaviours. For example, purported links with psychiatric hospital admissions, suicides, crisis calls and epileptic seizures have not stood up to scientific analysis.

So how could the phase of the moon affect us, even though our species is no longer exposed to the elements?

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.

Presumably this connection evolved over the hundreds of thousands of years when the moon’s cycles were more important for our survival.

Image credit: Luz Adriana Villa

How much do children’s bedtimes really matter for how their brains develop?

To measure the effects of bedtimes on cognitive function, researchers followed 11,000 children from when they were 3-years old to the age of 7 (Kelly et al., 2013).

Parents were asked about their children’s bedtimes at 3, 5 and 7-years-old. At 7, the children were tested on their reading, maths and spatial abilities.

The study found that:

“…irregular bedtimes at 3 years of age were associated with lower scores in reading, maths, and spatial awareness in both boys and girls, suggesting that around the age of 3 could be a sensitive period for cognitive development.”

In other words, regular bedtimes are important for both boys and girls and the earlier these can be implemented, the better for cognitive performance. The suggestion is that irregular sleeping patterns adversely affect development and these may cause permanent damage:

“Sleep is crucial for the maintenance of homeostasis and brain plasticity, including processes to do with embedding new knowledge, memory and skills into developing neural assemblies”

While is true of for both boys and girls, the study found that irregular bedtimes may be particularly bad news for girls.

Although children from more disadvantaged backgrounds tend to have less regular bedtimes, this was taken into account in the statistical models built by researchers:

“It might be that inconsistent bedtimes are a reflection of chaotic family settings and it is this, rather than disrupted sleep that impacts on cognitive performance in children. However, we found that inconsistent bedtimes were linked to markers of cognitive performance independent of multiple markers of stressful family environments. Findings from elsewhere suggest that stressful family environments affect children’s functioning via effects on sleep.”

Image credit: Patrick