Category Archives: General Interest

Can we modify specific stages of sleep to improve our memory?

Sleeping Kitten

Our memory is far from perfect. You have probably gone into another room and completely forgot what you went in there for. You stare into space and hope it will come back to you. Was it to pick up keys, tidy something or speak to someone? Nope, it just doesn’t come and you walk back slightly dazed and annoyed at your ailing memory. This is just a small example of the times our memory fail us during our day-to-day lives. However, what if we could improve our memory while we sleep?

Sleep is important. I’d like to think that I’ve impressed on you all by now. It protects us from certain metabolic disorders, keeps us alert to our surroundings and maintains our mental health and overall mood. There is some evidence to suggest it helps the brain’s natural waste disposal systems but that’s still in its very early days (despite some bold claims in the mainstream media). All of these areas have garnered substantial interest from scientists but memory is the one we’ll be focusing on. Typically, studies show that our ability to lay down new memories improves after a simple nap or a good night’s sleep. This, of course, isn’t always practical but it provides us some insight into what is happening in the brain when we drift off. It also should remind anyone revising for exams that sacrificing sleep is a false economy – unless of course you need to cram. Sleep can only help you so far there.

The link between sleep and memory raises an interesting question: what is it about this period of seeming inactivity that may help improve our memory? Sleep is far from a unitary construct and if we could identify the specific stage or stages which are crucial for memory then perhaps we could capitalise on this. We go through different stages of sleep, broadly, broken down into Non-REM and REM, and these are made up of different brain cell oscillations (see picture below) within the brain. Through probing the different stages, we can start to understand which are more important for memory. So, what are some of the candidates for sleep’s role in memory? The main contenders are sleep spindles and slow wave sleep (although REM has also been claimed to play a role in memory too).

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Stages of sleep recorded from EEG

Sleep spindles are characteristic of sleep stage 2 and are brief bursts of activity seen when using a brain imaging device known as electroencephalography (EEG). Imagine one of the funny caps with electrodes protruding out as you probably have a good idea of the typically EEG setup. Sleep spindles have been claimed to be important for memory consolidation and form a key part of one of the main hypotheses for how sleep might boost our memory. More specifically, it is argued that sleep spindles may facilitate the movement of memories from temporary consolidation in a part of the brain known as the hippocampus to the rest of the brain. Interestingly, sleep spindle activity correlates with performance on memory recall following sleep, and spindles show an increase following learning. The activity location of the spindles seems to be associated with the location of brain activity engaged during intensive learning of a specific function. As a result, some have suggested that sleep spindle activity may be used as a marker for learning potential (Fogel & Smith, 2011). However, the reality is likely more complex than this. Nonetheless, it does point towards spindles as a potential marker of memory consolidation during sleep.

In addition, slow wave activity (SWA) has also been shown to be important for memory. These are the slow (1Hz) oscillations characteristic of deep sleep. It has been this stage of sleep which has primarily been targeted to improve memory in previous studies. More recently, slow wave activity and sleep spindles have been successfully modified through the use of electrical stimulation of the scalp, drugs, playing sounds throughout the night (specifically timed and not so loud as to wake the participants), and even by presenting odours present at the time words were initially memorised.  These manipulations have been shown to improve memory and it seems it does this by increasing the amount of slow wave activity and sleep spindles. This work, although still in its infancy, suggests that it possible to stimulate specific features of sleep and, in turn, improve a vital cognitive function. It is at this point that a recent study in the aptly titled journal ‘Sleep’ comes in.

A group at the University of Helsinki in March this year (https://www.ncbi.nlm.nih.gov/pubmed/28364428) built on these previous findings by trying to identify a way to automate this process of stimulating slow wave activity. The success of this aim would increase the ease of introducing this technique into a home-setting and allow for the modification of sleep coveniently. The group decided to try to find a way to target sound stimuli to slow waves automatically in the hope of improving specific types of memory without affecting the sleep quality or mood of the participant. This is crucial as it is little use improving memory and modifying sleep if it causes other problems at the same time.

How did the researchers attempt to automate this process? They recorded electrical activity from the brain during sleep and were able to identify slow wave activity automatically by looking out for a specific frequency band (i.e. how often a waveform occurs over a set period of time). Whenever slow wave activity, indicative of deep sleep, was identified in the sleeping participant, a computer program sent a message to another device which played a brief sound. This meant that the sound was played just after a period of slow wave activity. Following this, there was a break of least 2 seconds between each sound being played. The loudness of the noise was changed automatically in response to cues from the participant. For example, if it seemed that the participant was waking up then the sound was lowered.

With the system in place, a total of 15 participants were invited into the lab for three days, each day separated by a week, to test out the automated approach to increase slow wave activity. The first day involved a familiarisation night so that the participants could get used to sleeping in the lab and with the equipment setup. During day two, one half of the participants heard the automated sounds and the other half did not. This was then switched for the third and final day. This allowed the researchers to compare performance on memory tasks when the sounds were not played and when they were not.

So, what did they find? Firstly, and importantly, they showed that their automated enhancement of slow wave activity was successful and viable. It managed to increase slow wave activity and sleep spindles. Moreover, the automated sounds were also found to increase memory overnight. They showed that word-pairs could be enhanced by playing a relatively quiet sound during slow wave activity. The interesting outcome of this study is that the possibility of having an automated system which people could use at home to boost memory. For populations who have poor memory this could hold promise as a therapeutic tool. It is a while off anything like this being available but it tells us something about how sleep contributes to memory and the potential ways we can exploit this in the future.

Although it is still unclear how exactly sleep is linked to memory, it is research like this which is starting to uncover that our brains are anything but quiet during sleep. Although there is likely to be no device which will improve your memory overnight on the market any time soon, scientists are working on the concepts necessary for this to become a reality. For now, perhaps you could try writing down what you’re about to do before walking into a new room?

ResearchBlogging.org Leminen MM, Virkkala J, Saure E, Paajanen T, Zee PC, Santostasi G, Hublin C, Müller K, Porkka-Heiskanen T, Huotilainen M, & Paunio T (2017). Enhanced Memory Consolidation Via Automatic Sound Stimulation During Non-REM Sleep. Sleep, 40 (3) PMID: 28364428

Additional References

Fogel, S. M., & Smith, C. T. (2011). The function of the sleep spindle: a physiological index of intelligence and a mechanism for sleep-dependent memory consolidation. Neuroscience & Biobehavioral Reviews, 35(5), 1154-1165.

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Sleeping Cat (Header)

Sleep Stages (Body Text)

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Should We Be Napping More?

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Please tweet me and other sleep scientists at the University of Manchester your sleep questions using the hashtag above! #msf16

 

“Why don’t you just take a nap if you’re so tired? It’ll probably help and give me a break from your whining…”

“I can’t nap! I feel all groggy after a nap. Besides, I find the complaining is helping me through the fatigue”

“…”

Napping is something which divides opinions. It’s no yeast-based snack featured heavily in the news recently, but there are certainly strong proponents of the will-nap and won’t-nap camps. However, what does the research say about napping? Can it help us get through the day and feel better able to deal with the challenges which face us?

Firstly, sleep in general is something taken for granted. We’re all guilty of it. On average we need about eight hours sleep, with some individual variation, but yet on average the general population is shy of this by one and a half hours. Although we should really be focusing on ensuring we get the right amount of sleep, at the right time, for our own body, it may be that napping may alleviate some of the symptoms of poor sleep such as fatigue and mood changes.

Regardless of your own personal views on this topic, it seems that naps are effective in easing fatigue, increasing our concentration, improving mood and even reaction times. Interestingly enough, even a relatively short nap of 10 minutes has been shown to improve alertness and decrease feelings of fatigue. Moreover, the positive effects were more immediate than for short (e.g. 10 minutes) compared to longer naps (e.g. 30 minutes). On a more practical level, there is evidence to suggest that a 15-minute nap could help reduce the number of road accidents.

It is key to remember that napping is a broad term. The short periods of sleep, typically during the day, which we call naps can vary in their duration and in the type of sleep which an individual might get. This could start to explain why some people love to nap and others despise it, but more on that later.

Great, so we should all be trying to sneak a nap in during office hours? Well you might want to think about the time at which you take a brief trip into sleep. During the average day, we tend to have a post-lunch dip in concentration and energy which lasts from around 1pm-4pm. Research has found that naps, whether brief or long, are most effective when taken during this post-lunch dip.

At this point, it looks like napping, albeit at the right time, can have some benefits. Yet, why might some people not actually end up benefiting? There are two possible explanations for this.

One is that disgruntled nappers may sleep for too long and focus on the grogginess upon awakening. The longer an individual naps for, the more likely they are to feel sluggish upon awakening – also referred to as sleep inertia. The positive effects of longer naps are felt for longer, but it takes longer for them to be realised.

Another explanation may depend on how serious nappers are about well… napping! Those who have more experience with napping were found to benefit more from a brief nap than those who don’t nap. This suggests that napping might have a greater effect for those who do it more frequently. Then again, it may simply be that habitual nappers are habitual because of the fact they benefit from those short slumbers. Rather than experience, it may just be individual differences. This is a question we don’t have the answer to quite yet before you try to discipline yourself into daily naps!

So what’s the verdict overall? Napping can be beneficial and if you can work through the sleep inertia longer naps will have a longer effect on your functioning. That been said, even naps as short as 10 minutes can have a positive impact. There are individual differences in our response to napping but that shouldn’t hinder us from feeling rested. Napping may be useful to ease fatigue but the ideal way to manage daytime sleepiness is to make sure you are getting better quality sleep during the night. Naps should not be a substitute for poor sleep if it can be helped!

One more thing…

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Time for ‘shameless plug time’. I am volunteering with the Manchester Science Festival as part of their sleep installation known as the Chronarium. It aims to immerse participants in specially selected lights and sounds which are used to promote relaxation and sleep. Would-be nappers are suspended in sturdy hammocks and are gently rocked into a peaceful state while the hustle and bustle of the busy shopping centre outside the fabric walls feels like a distant world.

The Chronarium is currently open as part of the Manchester Science Festival and can be found in the Manchester Arndale Centre. It is open until the 30th October. For those Mancunion readers amongst you, it’s free entry and well worth trying out!

Inquisitive Tortoise

References:

Tietzel, A. J., & Lack, L. C. (2002). The recuperative value of brief and ultra‐brief naps on alertness and cognitive performance. Journal of sleep research, 11(3), 213-218.

Brooks, A., & Lack, L. (2006). A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative?. SLEEP-NEW YORK THEN WESTCHESTER-, 29(6), 831.

Reyner, L. A., & Horne, J. A. (1997). Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology, 34(6), 721-725.

For more info on the Chronarium:

The Chronarium Sleep Lab

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Can a Lack of Sleep Kill You?

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“Have you forgotten so easily?” the subject asked. “We are you. We are the madness that lurks within you all, begging to be free at every moment in your deepest animal mind. We are what you hide from in your beds every night. We are what you sedate into silence and paralysis when you go to the nocturnal haven where we cannot tread.”

Surviving participant from ‘The Russian Sleep Experiment’ in the late 1940s. This volunteer went 15 days without sleep.

Before you start looking over your shoulder for the demonic presence presented above, don’t be alarmed. The quote above is from a piece of horror fiction from a website called Creepy Pasta and is completely fake. I hope.

I wanted to start with this as Halloween is fast approaching and I thought that a more fiendish sleep myth was worth looking at. Can a lack of sleep be directly responsible for your death?

A complete lack of sleep is something new parents and those of us with upcoming deadlines may know all too well. It’s draining, depressing, and leaves us eyeing up any available floor space as prime real-estate for your exhausted brain and body.

We have already looked at the effects of getting too little or too much sleep in my earlier post, but not the more extreme side of this. Research conducted with animals at the end of the 19th and the start of the 20th century suggests that not only is sleep important, but that it is vital for sustaining life. In experiments which looked at puppies, cats and rats, it was found that after anything from a few days to around a month of no to very little sleep would lead to death in these animals. This should be taken with a pinch of salt as animals tend to have to be forced to stay awake, and this is typically through stressful contraptions.

How about humans though? What is the longest any one has gone without sleep and gone on to tell the tale?

Well there are two main sources which we can look at. Firstly, there are the people who have willingly deprived themselves of sleep and secondly we can look at people who no longer sleep. Starting with those strange souls who willingly deprive themselves of shut-eye we can look towards a reality TV-show, our trusty sleep-deprived student population, and a couple of radio DJs to start to answer this question.

People are seemingly keen to show off their endurance when it comes to neglecting or overindulging in the necessities of life. Some will do it to win a fabulous prize and others because… Well I’m sure they know why they do it. Anyway, one such contest is relevant here.

The reality TV show ‘Shattered’ provided contestants a chance to win £100,000. All they had to do was be the last one standing in a competition to stay awake the longest. The show was screened on channel 4 in 2004 and its questionable premise didn’t put off a group of eager participants keen to deprive themselves of sleep for fame and glory. The winner stayed awake ultimately for 178 hours. The show capped the length of time participants could remain awake for, and a number of increasingly soporific tasks eventually weeded out one overall victor. If you are interested in this ‘experiment’ you can watch it here.

However, 178 hours was meagre compared to the next contenders. It seems that at the end of the 1950s and early 1960s there was a surge in radio DJs attempting to promote themselves and further their careers in bizarre ways. Collectively they felt that staying awake and parading their increasingly fatigued selves in a department store window was the way to do this.

Our first member of the media to tackle a lack of sleep was a young radio announcer referred to as W.A. He managed to stay awake for a total of 220 hours or just over 9 days. Previously, another radio DJ by the name of Peter Tripp had managed to last 201 hours without sleep. Finally, our last radio DJ, Tom Rounds, shortly after moving to Honolulu in 1959, managed to stay awake for 260 hours and appeared to suffer no long-term effects of his sleep deprivation.

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Is sleep necessary for sustaining life?

However, their collective records did not last long. The radio DJs were swiftly beaten in 1964 by the efforts of a student called Randy Gardener. Randy was a 17 years old student who felt that he could provide something more interesting than a papier-mâché volcano to present at his school’s science fair. He went without sleep for 264.4 hours, which equates to about 11 days and 24 minutes, and supposedly suffered no long-term problems. The often cited report claims that Randy suffered no ill effects of his experiment, yet others claim he experienced hallucinations, paranoia, fluctuations in mood, and problems in short term memory and concentration. The latter would fit with what we know about acute sleep disturbances (Petrovsky et al. 2014; Kahn-Greene et al., 2007).

Interesting, there have been reports of others having seemingly beaten Randy’s record and by a sizeable margin. These have not been validated in part due to scientists and those responsible for recording ‘world records’ not wanting to encourage these record attempts. For example, the Guinness Book of World Records no longer prints updates to the sleep deprivation record since Randy Gardener.

Okay, so far it looks like we can go a long time without sleep and survive. This seems to suggest that although we need sleep (try not sleeping tonight if you’re not convinced), an acute loss is not going to be directly responsible for your demise (but likely indirectly).

Let’s move to the second source of human sleep loss evidence now: those who no longer possess the ability to sleep.

We’ve already looked at people who for one reason or another have decided to willingly deprive themselves of sleep. Yet, for some the ability to sleep is lost. Although insomnia fits this bill, in this case we are referring to the rare genetic brain disease known as Fatal Familial Insomnia (FFI). As the name suggests, this disease is associated with a prolonged and severe insomnia which ultimately leads to death. There are some experimental treatments to delay the fatal consequences but these may only provide a couple of extra years at best.

Fatal familial insomnia is a prion disease. Prions are misfolded proteins that cause damage to the brain as they clump together. In the case of FFI, these prions clump at a specific part of the brain known as the thalamus. The thalamus plays a prominent role in regulating sleep and in coordinating the brain as it drifts deeper and deeper in somnolence. As a result, as the damage to the thalamus accumulates this unsurprisingly leads to worsening insomnia.

These individuals seemingly sleep very little or not at all and will survive from a few months to about several years following the presentation of symptoms. The course of this illness would suggest that it is possible to die from sleep deprivation, at least at extreme durations. However, we can’t say that it is the complete lack of sleep alone which kills those with FFI as damage to the thalamus affects other functions rather than just sleep. Moreover, as this disease is so rare that it would be wrong to make a firm conclusion based on this alone. More likely, it seems that the lack of sleep contributes significantly, but not completely, to the decline of those with this illness.

So, what’s the verdict on sleep deprivation being capable of deadly consequences?

The research in animals suggests it can be but the human studies tell another story. Although common myths and horror stories might like to toy with our inbuilt fears about the unknown, it looks like a lack of sleep will not directly lead to your death. Instead, the host of effects already covered may be the true driver between mortality and sleep loss.

Inquisitive Tortoise

References:

Luby, E. D., Frohman, C. E., Grisell, J. L., Lenzo, J. E., & Gottlieb, J. S. (1960). Sleep deprivation: effects on behavior, thinking, motor performance, and biological energy transfer systems. Psychosomatic Medicine, 22(3), 182-192.

Petrovsky, N., Ettinger, U., Hill, A., Frenzel, L., Meyhöfer, I., Wagner, M., … & Kumari, V. (2014). Sleep deprivation disrupts prepulse inhibition and induces psychosis-like symptoms in healthy humans. The Journal of Neuroscience, 34(27), 9134-9140.

** http://creepypasta.wikia.com/wiki/The_Russian_Sleep_Experiment

**In case you find yourself wanting to read the rest of the fictitious foray into the effects of sleep deprivation.

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Why Do We Sleep? Keeping Those Pesky Excitable Neurons in Line

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“The subject of sleeplessness is once more under public discussion. The hurry and excitement of modern life is quite correctly held to be responsible for much of the insomnia of which we hear: and most of the articles and letters are full of good advice to live more quietly and of platitudes concerning the harmfulness of rush and worry. The pity of it is that so many people are unable to follow this good advice and are obliged to lead a life of anxiety and high tension. Hence the search for some sovereign panacea…” (British Medical Journal, SEPT. 29, 1894, Sleeplessness)

I am sure until you glanced at the date you could easily be forgiven for thinking this quotation was written only last week. The disturbance of “modern life” is far from a novel phenomenon that plagues the 21st century, and smartphones and technology cannot be solely to blame for the problems we see. As the quotation continues (you can read the full article here, page 719), it is clear that attempts to treat insomnia were not all that different from remedies people might turn to now.

Disturbed sleep is something we’ve all experienced at one point or another. That sleepless night before an important meeting, interview, or exam stress leaves us feeling groggy, less responsive, and annoyingly less prepared for the problem we have to face. It’s clear that even a night of poor sleep can cause a plethora of problems which make restoration theories of sleep enticing and convincing. However, it is still not certain how sleep might rectify the impaired functioning associated with a night of tossing and turning in bed.

One theory argues that sleep acts to quieten down brain activity which becomes increasingly noisy during the day. This ‘noise’ makes it harder to function in terms of laying down new memories, remaining vigilant, and maintaining a positive mood. There are plenty of studies which highlight problems in each of these areas following poor, or a complete absence of, sleep for even a single night.

Now, the brain is a noisy organ and is constantly busy keeping you alive and functioning. Even when you’re not ‘thinking’ anything, it is still possible to detect a network of activity associated with this resting state. However, when ‘noisy’ is used here, it is in reference to noise which may be more indiscriminate and impede normal brain functioning.

Synaptic Homeostasis Hypothesis

This theory is known as the synaptic homeostasis hypothesis and was put forward in 2003 by the psychiatrist, Dr. Giulio Tononi of the University of Wisconsin-Madison. This theory centres on the important role of slow wave sleep (SWS) during a night’s sleep. SWS is the predominant neural signal found during the third stage of NREM sleep, and is characterised by slow-synchronised oscillations across the cortex. It is associated with the deepest stage of sleep and with many restorative properties of sleep.

A paper by Christoph Nissen and colleagues, published just this week in Nature Communications, has shed more light on how sleep may help us function on a day to day basis, and has provided further support for the synaptic homeostasis hypothesis. Currently, most of the evidence for this theory comes from animal studies and indirect evidence from a handful of human studies. That is what made the recent study by Nissen particularly exciting.

Christoph Nissen and colleagues at the University of Freiburg explored how sleep, compared to sleep deprivation, was associated with changes in memory encoding, cortical excitability and neural mechanisms behind brain plasticity and learning. They examined a group of 20 healthy university students who all took part in the normal sleep and sleep deprivation portions of the experiment.

The team examined cortical excitability following a normal night’s sleep and sleep deprivation using transcranial magnetic stimulation (TMS) to induce a twitch in a participant’s hand. The TMS device allows scientists to deliver a pulse which can be used to inhibit or excite the neurons underneath its coil. A pulse to the appropriate location on the right side of the brain will produce a corresponding twitch to the muscle in the participant’s left hand. The strength of the pulse needed to produce a response, or twitch, can be used as a marker of how excitable that particular patch of neurons is. As a result, this technique provides a non-invasive and relatively simple way to test one of the synaptic homeostasis hypothesis’ predictions.

In addition, the group examined brain activity using electroencephalography (EEG) to further explore alterations produced by extended wakefulness.They also tested performance by examining participant’s memory through the use of a simple word pair test, and through their capacity for LTP-like plasticity using a paired stimulation method.  LTP, or long-term potentiation to give it its full name, has been argued to be the mechanism within the nervous system through which learning occurs. It is argued to play a large role in memory formation and so provides the researchers with another way to assess performance following extended wakefulness or sleep.

In their student sample, Nissen and colleagues found evidence of increased cortical excitability, poorer memory performance, and reduced LTP-like plasticity following a night of sleep deprivation compared to wakefulness. All of these support the synaptic homeostasis hypothesis and support the role of sleep in ‘resetting’ the neural activity to a baseline. It is argued that this is what allows us to continue on at our best after a night’s sleep and allows us to start efficiently storing memories of cute animal videos while at work.

Yet, the evidence for this is still in its infancy and it would be unwise to jump to conclusions about this research. Rather, it is another hat to throw into the ring of sleep science.

This work is still just a start, but it is an interesting and exciting foray into further understanding how sleep serves its important role in our lives. Furthermore, it also provides some interesting avenues for therapies which might try to capitalise on the ability of sleep to return neural activity to a set-point. There is already some evidence to support short-term sleep deprivation to help depression. A further understanding of sleep’s impact on the brain, or lack thereof, may help us manipulate this to our advantage.

Inquisitive Tortoise

References:

Kuhn, M. et al. Sleep recalibrates homeostatic and associative synaptic plasticity in the human cortex. Nat. Commun. 7:12455

Tononi, G., & Cirelli, C. (2003). Sleep and synaptic homeostasis: a hypothesis. Brain research bulletin, 62(2), 143-150.

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Sleep Roundup 12/07/16

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So, being the geek that I am I come across lots of interesting sleep talks online and resources which help me with my day to day research. Here’s a roundup of the current sleep talks / podcasts online over this past week or so which grabbed my attention.

This may become a regular thing if I find enough interesting sleep research / talks (organisation permitting, no doubt).

For now enjoy two the latest episode of the Infinite Monkey Cage which is focused on sleep in general and How Much Sleep Do We Need from the BBC. Also, if you don’t already listen to the infinite monkey cage, do so now!

Inquisitive Tortoise

 

 

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Sleep Trackers: Do They Work?

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“What makes a good sleep tracker?”

“I didn’t sleep too well last night, and I felt so groggy this morning”

“Stressful day at work?”

“No, my stupid SleepApp didn’t work properly and I spent the night trying to get it to play relaxing whale noises. When I did drift off by myself, it didn’t wake me up in between sleep cycles. It better not fail tonight, I’ve got an important meeting tomorrow and I can’t sleep properly without it…”

“Uh-huh…”

Stilted conversation aside, we spend a large amount of our daily lives glued to screens of some description. These keep us active and engaged well beyond the time when we should be switching off for the night. For example, light from phones and laptops can alter our normal patterns of sleep and make it harder for us to drift off in the evening. This plays havoc with the body’s multitudinous clocks which naturally set in motion a number of chemical changes that allow us to unwind steadily before we drift off to sleep. However, that’s a point for another day.

For now, I want to talk about how we use technology to seemingly help us get to sleep and to, in want of a better way of putting it, tell us that we were in fact asleep the previous night (with or without a pretty graph to go with it).

Commercial ways to assess sleep:

There were two main ways of objectively measuring sleep in the research community: actigraphy and polysomnography (See what makes a good sleep tracker?) However, the business world has managed to split this up into a large selection of methods to tell us whether we’re sleeping enough. It may be that these different commercially available devices and apps are actually pretty good but the available evidence tells a different story.

Types of Sleep Tracker

I won’t go into too much detail about all of the different types of sleep tracking devices, of which there are many, but the purpose of the below list is to show the range of ways you can measure your sleep outside of the lab.

Movement-Based

Sleep apps developed for use on phones (e.g. Android or Apple stores) vary in cost and features which they promise. A popular sleep app for android users, ‘Sleep as Android’, has over 10 million downloads and boasts the ability to differentiate between wakefulness, light sleep and deep sleep. It also claims that it can wake you up during your lightest sleep stages in the morning to promote a “natural” awakening which supposedly avoids the grogginess and tiredness of waking up in the deeper stages of sleep. This app, amongst others, relies on movement-based information.

Movement-based trackers can also take the form of watches which track our sleep (alongside activity, exercise, and heart rate). Both of these aim to give us lots of detail about our sleep and provide us with statistics which try to educate us about our own sleep – mainly with the intention of helping you sleep better. These works by applying an algorithm to movement data which is logged by something called an accelerometer. This is already present in your mobile phone and the app simply makes use of this data to predict your sleep.

Brain-activity Based

There are a number of devices which you can buy which will offer a rudimentary attempt to track brain activity. Typically, if you want a good picture of your sleep you will track a wide range of different bodily functions in something known as polysomnography (see what makes a good sleep tracker?) However, these trackers try to track sleep through the use of a couple of electrodes placed on the scalp during sleep.

Temperature / Heart Rate / Muscle Response Based

Typically, these will be used alongside movement data to attempt to give a more accurate estimate of sleep.

Bed-Based

Again, these are technically based on movement and temperature data but are placed on the bed in some respect and not worn. These can take the form of a bed covering (link), or even a trendy looking ball such as Sense.

What makes a good sleep tracker?

So what does an ideal measurement of sleep look like?

Polysomnography

The gold-standard measure of sleep is known as called polysomnography. This measures a number of different things including:

  • Electroencephalogram (EEG; records electrical activity produced by cells in the brain)
  • Electrooculography (EOG; records eye movements)
  • Electromyography (EMG; records electrical activity generated by muscle activity)
  • Cardiac rhythms (ECG)
  • Respiratory activity

This setup, understandably, requires you to come into a sleep laboratory and sleep in a rather unfamiliar bed with electrodes planted on your head and body. This enables sleep researchers to record brain activity, eye movements, muscle activity and heart rhythms. Together, these readings allow us to identify how long you sleep, how often you wake up, how long it takes for you to get to sleep, when you wake up, and to identify the individual sleep stages and cycles which make up a normal night’s sleep. There are problems with this approach but it is the best option we have for understanding more about an individual’s sleep. As you’ll likely agree, this is a lot of information to obtain and wade through. Sleep apps and watches cannot possible recreate this and so are limited, but this is not necessarily a problem if they correlate well with other less rigorous but well accepted measures used in sleep research.

For example, most sleep apps and watches work by determining how often you move on a given night and use the times you are moving less as sleep and the times you are moving more as awake. These devices measure movement by using a little device called an accelerometer which is found within your smartphone and watches such as the FitBit.

Actigraphy

Within sleep research, we also use a device which is based on this same technology. The device is known as an actigraphy watch and it is generally seen an acceptable alternative to sleep lab measurements which are often costly, time-consuming and cumbersome. An actigraphy watch is usually worn on the non-dominant wrist, can be used outside a sleep lab, and thus allows researchers to assess sleep objectively as people go about their normal day-to-day lives. Actigraphy also works by detecting movement through accelerometers, and algorithms are applied to this data to explore certain facets of sleep (there are limits to this) in a more portable format.

Do these sleep apps actually work?

The main question you’ve probably come here to hear answered. The short answer: yes, but there are limitations to them all.

Quite simply put, there is a lack of research conducted here and the sample sizes are miniscule at best for the ones that do currently exist. Yet, these research studies do hint that perhaps sleep apps and wearable devices are actually assessing your levels of sleep in terms of duration, sleep efficiency and how often and for how long you are awake during a night of recording.

When sleep researchers try to determine whether wearables are actually tracking sleep they look for the following things: sensitivity (e.g. the ability of the app / device to measure when you’re actually asleep), specificity (e.g. the ability of the app / device to measure when you’re actually awake) and accuracy (e.g. is it measuring when you’re truly awake and truly asleep).

What does the current science say about commercial sleep trackers (e.g. FitBit)?

Wearables, or commercial sleep trackers, tend to show the same pattern when it comes to estimating our sleep patterns as that which is seen in actigraphy. Wearables using movement data typically overestimate total sleep time and sleep latency (how long it takes you to fall asleep) but are generally pretty accurate at telling when you’re asleep and for how long. By contrast, wearables such as the FitBit are poor at identifying periods of wakefulness during the night and will significantly underestimate disruptions in the night – known as wake after sleep onset (WASO). So, for the average person it is fair to say that wearables such as the numerous reincarnations of the FitBit may give you some insight into what your sleep looks like. However, if you are prone to fitful sleep or suffering from insomnia then these apps will be less accurate (despite claims on FitBit’s website that they may have a fix for people with disrupted sleep) and should not be depended upon. This is doubly the case if you consider using these in lieu of a going to a doctor about your sleep issues.

How about the claims made by, worryingly, many sleep apps and wearables that they can track different stages of sleep? The bold claim that a sleep app can measure REM sleep, for a start, is simply not known and extremely doubtful, even if some apps do add in more than just movement measures (e.g. heart rate). Other wearables such as the Jawbone UP make more reasonable claims that they can detect “light” versus “sound” sleep over a given night. Although it’s not entirely clear what “sound” sleep actually means, one research team took this to mean deep sleep and examined whether there was any truth behind this claim. In a large sample of adolescents, they found that the light and sound sleep measures were rather poor at measuring what they claimed to. Rather worryingly the ‘light’ sleep was found to be associated with time spent in the deepest stage of sleep which highlights that healthy skepticism should be applied to apps claiming they can pick out individual, or broad, sleep stages (see further reading).

Further Reading

A study by de Zambotti and colleagues examined the sensitivity and specificity of a different wearable, the Jawbone UP, compared to polysomnography and actigraphy in a group of middle aged women (average age 50 years old). They found, like others, that the Jawbone UP was generally accurate at determining when and for how long participants slept (but overestimated this value), but was pretty poor at determining when participants woke up during the night (underestimated this value, so had a good sensitivity but poor specificity). The ability to detect periods of waking and total sleep during the night were notably bad during particularly disrupted sleep as detected by PSG. This suggests that the Jawbone UP and FitBit Ultra are not particularly accurate at detecting the amount of sleep and waking in individuals with disrupted / fragmented sleep.

When the same research group (de Zambotti et al., 2015b) also examined the Jawbone UP in a sample of adolescents and young adults (age range 12-22 years old) and found similar results. That is, that the Jawbone UP overestimated total sleep time, sleep efficiency and sleep onset latency but underestimated total wake time during the night (it was much worse at detecting time spent awake than any of the sleep measures). Overall, it was found that the Jawbone UP was good at detecting when participants were asleep, but rather poor at identifying when they woke up during the night. This is important as fragmentation of your sleep will impact on sleep quality.

The same study also tried to examine whether the Jawbone UP’s dichotomisation of ‘sound sleep’ versus ‘light sleep’ were appropriately linked to deep versus light stages of sleep as assessed in the sleep laboratory. The ‘light sleep’ count was linked to movement and awakenings, and also to stage 3 of sleep (known as the deepest stage of sleep). In fact, none of the lightest stages of sleep were shown to be associated with the ‘light sleep’ count produced by Jawbone UP. The opposite was found for the ‘sound sleep’ count whereby typically deep stages of sleep were not found to be associated with this measure, but rather overall measurement of movement (specifically reduced movements) was. This suggests that wearables such as Jawbone and FitBit may be reasonable at detecting sleep during the night, but not night-time awakenings or the different stages of sleep. Furthermore, in populations where sleep is fitful or fragmented the accuracy of these apps reduces to a greater extent.

A previous study by one of the study’s authors, Hawley Montgomery, in 2012 found that a wrist-worn FitBit was comparable to actigraphy, but poorer than polysomnography in detecting when people were asleep. However, the FitBit was particularly poor in identifying when people woke up compared to actigraphy. This suggests that the healthy adult populations could still gain useful information from a FitBit but, as the authors highlight, it is a far way off being appropriate for measuring sleep in people with diagnosed or suspected sleep disorders.

As you can hopefully see, there are only a handful of studies which have attempted to understand how good market-leading wearables are in detecting sleep and wake. The emphasis on sleep and wake is intentional. These apps have not been assessed for their ability to assess anything beyond total sleep time, wake after sleep onset, sleep onset latency and sleep efficiency.

Smart Alarms

Other sleep apps also include a measure to wake individuals up during the lighter stages of sleep to enable them to feel more wakeful in the morning. The alarm sounds after tracking an individual’s pattern of sleep to create an ‘optimal’ window to wake up during which the alarm will try to target. Alarm PicHowever, there is currently limited evidence to back up these claims (Kelly et al., 2012), and there needs to be considerably more research here before such claims can be validated and backed up (SLEEPIO Article). It is somewhat surprising that such research has not been carried out considering how easy it would be to create an experiment where participants are randomized to either an optimal or sub-optimal wake-up alarm condition over 1-2 weeks (See Kelly et al., 2012 for expansion on this very point).

Concluding Thoughts

Sleep is something which can be fickle at many times throughout our lives, and it is not surprising that we would want to learn more about it. However, for those of us who suffer with our sleep on a regular basis, there is an obvious appeal to be able to track our sleep in the comfort of our own homes and on a regular (perhaps even nightly) basis. It may provide a skewed notion of how an individual is sleeping (for better or for worse) and this can provide unfounded alarm or comfort. The current wearables have a reasonable ability to tell when and for how long you’re asleep but be sceptical on their ability to tell you anything about the quality of your sleep. If you are genuinely concerned about your sleep then please consult your doctor.

Sleep apps, wearables and other sleep trackers are a fantastic idea and if they can prove to be comparable to other methods such as actigraphy then I see few reasons to discourage their use. However, there is a lack of available data to really understand whether these different sleep trackers are accurate. If they are simply measuring time spent asleep and awake then they seem to be okay, and comparable to measures used in sleep experiments. Yet, bolder claims about smart alarms, tracking individual sleep stages, and their use in sleep disorders are not conclusively studied at this moment in time. That is not to say they will not, but there is a sensible reason to be cautious until that evidence is available to us. So, by all means use these trackers and add them to part of your daily routine if you so wish. However, understand their limitations and be aware that paying minute detail to your sleep may also create its own problems. More on that point in my next post.

Inquisitive Tortoise

References

de Zambotti, M., Baker, F. C., & Colrain, I. M. (2014). Validation of Sleep-Tracking Technology Compared with Polysomnography in Adolescents. Sleep, 38(9), 1461-1468.

de Zambotti, M., Claudatos, S., Inkelis, S., Colrain, I. M., & Baker, F. C. (2015). Evaluation of a consumer fitness-tracking device to assess sleep in adults. Chronobiology international, 32(7), 1024-1028.

** Kelly, J. M., Strecker, R. E., & Bianchi, M. T. (2012). Recent developments in home sleep-monitoring devices. ISRN neurology, 2012. (Good expansion on the different sleep trackers available)

Montgomery-Downs, H. E., Insana, S. P., & Bond, J. A. (2012). Movement toward a novel activity monitoring device. Sleep and Breathing, 16(3), 913-917.

Montgomery-Downs, H. E., Insana, S. P., & Bond, J. A. (2012). Movement toward a novel activity monitoring device. Sleep and Breathing, 16(3), 913-917.

Further Reading

http://www.huffingtonpost.com/dr-christopher-winter/sleep-tips_b_4792760.html

https://www.sleepio.com/articles/sleep-aids/sleep-apps/

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Main Pic

Alarm Pic

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Sleep Snippet: Why Bother Even Trying to Understand Sleep?

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Sleep in its natural environment.

It’s a fair question (although don’t tell my supervisors that I said that…) We enjoy doing it, it refreshes us, and we tend to find ourselves doing it in any spot we find ourselves last thing on a Wednesday afternoon. Most of us could identify that we need sleep and that it helps maintain the brain and body in some way but why do we need to go any further than that, other than for pure curiosity?

Sleep is important for our ability to function in the world about us. As we are likely all aware, a night without sleep or a few days with very little sleep can make it incredibly hard to do much of anything. We find it hard to concentrate on conversations with colleagues or friends, find ourselves becoming more forgetful and start to see every nook and cranny as ideal spots for a quick nap. In addition, we become more irritable and may find it harder in general to control our emotions. If we have been deprived of sleep for long enough, we may even start to see and hear things which are not really there and become increasingly paranoid.

For most of us these experiences are temporary and we can largely shrug off the negative effects of too little sleep by making sure we go back to a regular routine of sufficient sleep. However, what about those who can’t? What about people who struggle to sleep at all and who do not feel rested after a night in bed? It is important to understand a) why these individuals struggle with sleep and b) how poor sleep leads them to experience the negative side-effects we all do but to a much greater degree? The second question, in part, can be understood by trying to explore the effect of a lack of sleep on relatively healthy individuals like you and me.

The importance in understanding why we sleep and how this should look in the brain lies in how we can use that knowledge to help those who can’t sleep or whose sleep is disturbed significantly. This can involve those who suffer from sleep disorders such as insomnia (where we don’t sleep enough), hypersomnia (where we sleep too much), and narcolepsy (where we unexpectedly fall asleep throughout the day) to name a few examples.

We can also look at the role of sleep difficulties in the context of other illnesses, where problems drifting off to sleep and staying so can exacerbate or lead to many different symptoms of disease. For example, sleep difficulties have been implicated in many mental illnesses such as schizophrenia, depression and anxiety disorders. In fact, around 80% of individuals with schizophrenia will experience some form of sleep disruption. Sleep difficulties have also been shown to have an influence on diseases of the immune system such as ulcerative colitis, psoriasis, and in neurological conditions such as Parkinson’s disease. I am very conscious of how many different disorders I could list where an understanding of sleep could help to reduce suffering but that might make for a rather boring article (and not help with my self-imposed word limit…) Through understanding sleep, we can understand these related illnesses to a greater extent and hopefully provide better treatments for patients.

Hopefully, in this short snippet of an article has shown that understanding why and how we sleep is important and worthwhile.

Inquisitive Tortoise

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Header Image: Sleep in Society

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The Creature at the End of the Bed: What is Sleep Paralysis?

Sleep Paralysis

A fitting depiction of the sleep paralysis experience for many.

My limbs won’t move. I can’t scan the room or, more importantly, run if I needed to. This feeling in itself is terrifying, but I become aware of an evil presence in the room. It’s behind me and is waiting there. All I’m aware of is a jagged shadow which means me some ill. I’m desperate to move, to escape, to scream out and run from this figure watching me. Minutes pass and my focus is on moving, willing my failing limbs to spring into action. Suddenly they return back to life and I instinctively look towards the corner of the room where I felt a malevolent being was sizing me up. There’s nothing there but darkness and my old blue wooden wardrobe. Shaken and tired, I attempt to drift back to sleep and forget that the shadow could still be out there.

My first, and only, experience with sleep paralysis occurred when I was about 6 years old and coincided with my sleep-walking phase. It was a brief but terrifying experience and although I don’t remember it perfectly, the feeling of vulnerability and that shadow’s presence remain with me.  The experience of sleep paralysis differs from person to person but there are constants to everyone’s experience. There is the characteristic paralysis of voluntary muscles and often, but not always, this is accompanied by hallucinations which can leave the person frightened and disoriented. The hallucinations experienced by sufferers of sleep paralysis also appear deeply embedded in different cultures, literature and history (see sleep paralysis as a cultural phenomenon below).

These hallucinations can be grouped into intruder, incubus and vestibular hallucinations. The intruder hallucination, whereby there is a feeling that there is a being in the room with you, with the feeling of malevolent intent is the type I experienced as a young child. However, experiences of a great weight on your chest attributed to a demon-like creature and the feeling of floating can be identified as incubus and vestibular hallucinations respectively. These experiences are particularly distressing for those who are unfamiliar with their cause and has led some to wrongly believe they were suffering from psychosis.

Although a bizarre experience, it is not all that uncommon. A large systematic review (a comprehensive report which gathers all of the studies, in theory, ever conducted on a topic) of the prevalence of sleep paralysis found that “7.6% of the general population, 28.3% of the student population, and 31.9% of psychiatric patients experienced at least one episode of sleep paralysis” (Sharpless & Barber, 2011). It’s interesting to note that it should be so prevalent amongst student populations.

So, what is at the root of sleep paralysis episodes? It appears that sleep paralysis is linked to REM sleep and the transition to and from this stage of the sleep cycle. Interestingly, in a sleep disorder known as narcolepsy, characterised by sudden onsets of sleep, the prevalence of sleep paralysis is around 50%. This is considerably higher than the normal population, and it might be due to the sudden onset of REM sleep seen in individuals with narcolepsy. Moreover, narcolepsy is also associated with partial sleep paralysis. This is where there is some limited movement available to the individual but they are likely paralysed and experience the powerful and frightening hallucinations seen in sleep paralysis.

In my last article, I talked about how it is possible to induce sleepwalking in those with a genetic risk by sleep depriving them. It appears that the same trick can be useful in eliciting sleep paralysis episodes in students. A study by Takeuchi and colleagues (1992) showed that by waking students up at just the right time they were able to elicit sleep paralysis in their sample. More specifically, by waking up participants when they were just about to enter REM, they were able to manipulate it so that participants were more likely to go directly into REM sleep as they drifted off again. However, this technique is far from perfect in eliciting sleep paralysis as out of 64 successful REM interruptions, only 6 episodes of sleep paralysis were recorded in 5 out of 16 participants. This suggests that sleep onset REM is involved in sleep paralysis but there are likely other factors which play a role here. For example, stress and physical tiredness (beyond being woken up in a sleep laboratory) may also contribute to the likeliness of sleep paralysis occurring. This may explain why student and psychiatric populations are more prone to sleep paralysis episodes.

As I have already, hopefully, addressed with sleepwalking, there is a clear and long history of sleep paralysis as recorded in literature and historical medical reports. We have identified the different subtypes, linked it to a particular stage of sleep and started to identify some connections with other sleep disorders (e.g. narcolepsy). However, this is largely where our understanding of the phenomenon ends. It appears that problems in the REM stage of sleep are important in the production of sleep paralysis but more work is needed to understand what these are and why they are important.

Sleep Paralysis as a Cultural Phenomenon

S5765870281_a51d288e54_zleep paralysis occurs across a wide range of different cultures and there is historical evidence of it occurring throughout the history of medicine and literature. Folk terms such as the “old hag”, the “Pandafeche”, and visitations by demonic presences such as succubi and incubi have been attributed to sleep paralysis.
Many of these lay blame for experiences on paranormal or spiritual beings, with a focus on witch or ghost-like beings (old hag and pandafeche), and given the content of hallucinations experienced alongside sleep paralysis this is not surprising.

The painting, ‘The Nightmare’ by Henry Fuseli is commonly believed to be a depiction of sleep paralysis and a case study from the 1600s exists which describes sleep paralysis in vivid detail (Kompanje, 2008). Interestingly, the previous case study also highlighted how body position while sleeping might contribute to sleep paralysis and hallucinations experienced with it. There is some recent evidence which suggests that lying in a supine position (on your back, face up) may be associated with increased rates of sleep paralysis and associated hallucinations. The 17th century case study provided the earliest evidence of this facet of sleep paralysis.

Inquisitive Tortoise

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Header Image: Sleep-paralysis-pic 

Additional Info Image: Demon

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