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


“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


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.

Image Credits:

Header image

Leave a comment

Filed under General Interest, PhD, Sleep Science

Why Do We Sleep? The Brain’s Waste Disposal System

Brain Pic

How does sleep help this fellow’s tubular brain remain healthy?

“Okay, smart guy so why do we sleep then? Bet you can’t answer that one…”

“Well… How long have you got? There’s a fair bit of content to co- Hey! Don’t run away! It won’t take me that long, honest!”

Sleep is complex and despite the intuitive explanation for why we drift off on a daily basis, we are still in our infancy when it comes to understanding how and why this occurs. We know that for the most part a good night’s sleep is refreshing and important for paying attention at work, school, or carrying out most tasks.However, how sleep keeps us functioning is less black and white.

There is no one reason why we need to sleep. For example, it maintains us mentally and physically in a number of ways, including:

  • Memory consolidation
  • Growth
  • Mental health
  • Brain maintenance

We could spend a lot of time covering all of these in considerable detail, but for now we’ll look at brain maintenance. Brain maintenance may seem like a broad category but it fits into our recent developments in understanding how the brain deals with waste materials.

The Brain’s Waste Disposal System

All cells in the body produce waste products of some description. This may be as a result of metabolic functioning, protein synthesis, and cell death, and these are filtered out via the lymphatic system.

The brain, unsurprisingly, is no different. However, until recently it was not clear how the brain solved this waste management problem. That was until the recent discovery of the glymphatic system.

Glymphatic System: The Brain’s Clearance System?

So what is the glymphatic system, and why should we care? Well firstly, its discovery has been hailed as important step in understanding major neuropathologies such as Alzheimer’s disease. Although, there’s a while to go before we should get too excited about this.

As mentioned above, the cells within your body work and produce potentially toxic waste products. The body has an effective way of getting rid of these through multitudinous lymphatic vessels. Yet, until recently it wasn’t known how the central nervous system, that is the spinal cord and the brain, manage to remove their waste products.

In a similar way to the lymphatic system, it has been proposed than the glymphatic system works by removing waste products from the central nervous system (e.g. spinal cord and brain). This is achieved, in part, by the exchange of solutes or waste products between cerebrospinal fluid (CSF) and interstitial fluid (ISF).

The system is comprised of a series of channels which appears to “piggyback” off blood vessels within the brain. It is argued that the movement of arteries, as a result of blood-flow, helps to move the cerebrospinal fluid through the brain (CSF). This enables the movements of waste between interstitial fluid (ISF) which bathes cells and CSF which runs alongside blood vessels in the brain. However, the glymphatic system also includes the presence of specific glial cells, known as astrocytes, alongside these channels. The function of the astrocytes is to facilitate the movement of particles between CSF and ISF. Without their presence, the movement of waste would be too sluggish to respond appropriately to the changing demands of the hungry organ we call the brain. It is the presence of glial cells, and the similarities to the lymphatic system, which give this glymphatic system its name.

Waste Disposal While You Sleep

How does all of this relate to sleep? Well, a recent collection of studies has provided some evidence that sleep may facilitate the movement of toxins from the brain via the increased activity of the glymphatic system.

One particular toxin produced as a waste product of brain cell activity is called amyloid beta. This toxin is linked to severe progressive diseases such as Alzheimer’s, and there is considerable research trying to work out how to mitigate its destructive effects. Last year, a group of scientists lead by Professor Maiken Nedergaard at the University of Rochester Medical Centre found that the brain’s drainage of amyloid beta was increased during sleep and anaesthesia-induced unconsciousness compared to during wakefulness in mice. More specifically, it seems that the capacity of the brain to flush out such harmful toxins is enhanced due to the area between cells, interstitial space, expanding by as much as 60 per cent. This seemingly enables a greater opportunity for such toxins to be removed via the glymphatic system.

In addition, the same group also found earlier this year that this process of washing harmful toxins out of the brain during sleep is enhanced based on the position of the mice studied. It was found that the removal of amyloid beta was enhanced when the mice slept on their side rather than their back. Interestingly, in both cases, it seems that anaesthetised mice showed the same effects as sleeping mice for the removal of amyloid beta and benefit of sleep posture.

This suggests that sleep may help with the maintenance of our brains by enhancing the waste disposal system we have in place. It may also provide some evidence as to why dementia and serious psychiatric illnesses are associated with sleep disturbances prior to the emergence of symptoms. However, this is all speculative and uncertain at this point. For a start, these studies have only been conducted on mice, and due to the nature of the experiment it is not likely that they would be conducted on humans any time soon. That’s not to say that the same mechanism might not be occurring within humans, but it is rash to jump the gun and assume it is.

Regardless, it will be exciting to see how research in this area advances and what it can teach us about the importance of sleep.

Inquisitive Tortoise


Lee, H., Xie, L., Yu, M., Kang, H., Feng, T., Deane, R., … & Benveniste, H. (2015). The effect of body posture on brain glymphatic transport. The Journal of Neuroscience, 35(31), 11034-11044.

Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., … & Takano, T. (2013). Sleep drives metabolite clearance from the adult brain.science, 342(6156), 373-377.

Further Reading:

https://www.urmc.rochester.edu/labs/Nedergaard-Lab/projects/glymphatic_system (From the horse’s mouth; a better description of what I’ve tried to convey in this post!)

Image Credits:

Header image

Leave a comment

Filed under Psychology, Sleep Science

Sleep Roundup 12/07/16


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



Leave a comment

Filed under General Interest, Media, Sleep Science

Sleep Trackers: Do They Work?

Main Pic

“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…”


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.


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.


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?


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.


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


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



Image Credits:

Main Pic

Alarm Pic

Leave a comment

Filed under General Interest, PhD, Psychology, Sleep Science

The Science Room

I recently wrote another science thing! This time it’s not about sleep but I imagine it’s something which some of you will find interesting. Please check it out and make sure you direct any interesting science questions to the Science Room too!


Leave a comment

Filed under Uncategorized

Somniloquy: What causes sleep talking?


Sleep(ing) is tricky.

We’ve already covered sleepwalking in some detail and identified how complex behaviours can be initiated during a period of seeming unconsciousness. These behaviours can take a wide range of different forms. For example, reports of sleep-texting are becoming more common, which highlights how changes in our daily routines lead to changes in the type of sleepwalking behaviours. Next on our list is to shed some light on why we might talk in our sleep too.

“Jack…? Are you awake? What’re you talking about?”

“Ignore him, he’s speaking in devil-speak again. He does that.  Admittedly, it’d be less freaky if he didn’t have his eyes open at the same time too…”

Apparently I didn’t form full sentences in my sleep during my spate of sleep-related weirdness as a child, but sounds resembling more than mumbling could be identified by friends whenever I stopped over. Alongside the heart-attack-inducing brush with sleepwalking which my parents were forced to endure, I also ‘entertained’ my friends by talking in my sleep – or engaging in somniloquy, as it’s also known.

Sleep talking is an experience which many of us will come across at some point in our lives.  It is a relatively common phenomenon and can be found predominantly during childhood, but also as a rarer occurrence within adulthood. However, the prevalence in adulthood varies considerably. It is one of the most frequent parasomnias (disorders of sleep which involve some form of unusual or unwanted behaviour during sleep) found between the ages of 3-13 years old (Laberge et al., 2000), and it appears slightly more often in boys of this age than girls.

Sleep talking is associated with sleepwalking, and one may predict the subsequent occurrence of the other (Ohayon et al., 1999). This is not surprising, as many parasomnias are found together, or increase the likelihood of someone experiencing another. The main concern during adulthood is the potential embarrassment which might come alongside the sometimes nonsensical muttering, and potentially the content which is said. However, it is generally accepted that sleep talking, although impressively coherent at times, is not necessarily truthful or meaningful. For example, it is not admissible in court and the individual will have no memory of what they said or even that they were talking in their sleep. This is part of the reason why it is so tricky to work out the prevalence of sleep talking in adults.

When does sleep talking occur? Well, like many other parasomnias, it appears that it can occur across the sleep-cycle. The quality and coherence of the speech during sleep may differ as an individual goes from light, deep and finally to REM sleep. The exact link between sleep stage and speech is uncertain, but it has been argued that REM sleep is associated with more coherent and daytime-like conversations. There is also evidence to suggest that it runs in families, although environmental factors may make it more likely.

What causes sleep-talking and should we be concerned? For the majority of us, no. It is a harmless, if amusing, occurrence and may only occur in episodes which can be traced to an environmental cause. For example, it can be brought on by a number of factors such as sleep deprivation, stress, alcohol and fever. However, there may be problems associated with the effect of sleep talking on a bed-partner. This may produce problems in the person who shares the bed with the sleep-talker, who may find themselves being kept up and experiencing insomnia-like symptoms. Some studies have highlighted a link between adult sleep talking and some psychiatric illnesses, but it is far from conclusive what the nature of this link is. For the most part, sleep talking is a harmless, if slightly embarrassing, behaviour.

Sleep talking can also occur in the context of other illnesses such as night terror, nightmares, sleep apnea and REM behaviour disorder (RBD).

Other areas in which sleep talking may occur:

Night Terrors

One way in which we can explore sleep-talking is in the presence of noted disorders during sleep. One example, where sleep-talking and movement are found, is night terrors. These are a form of sleep disturbance which occurs mainly during childhood. They are characterised by thrashing, panicked-like behaviour and screaming which occurs for several minutes. The child has no memory of this, and it can be considered a disorder of arousal like sleepwalking. In a similar manner, they can be exacerbated by anxiety, poor sleep schedules and behaviours which disrupt sleep (e.g. needing to go the toilet). Although this is not your archetypal description of sleep-talking, it is an example of how the boundaries between sleep and wake are blurred.

REM Behaviour Disorder

This is another disorder of arousal and, like night terrors, also involves elaborate movement and speech during a period of sleep. This occurs more commonly during middle age and is associated with more insidious origins such as the onset of Parkinson’s disease. At a basic level, RBD can be considered the acting of dreams, and the behaviours shown typically match with dreams had by the individual with RBD. However, dream ‘enactment’ can occur alongside many other sleep disorders, and the diagnosis of the disorder needs to be confirmed with the use of methods to study brain and muscle activity during sleep.

It’s important to note for that all the knowledge which we have amassed on the topic of sleep, we are still uncertain about so many different aspects of it. Sleep-talking fits into that snugly, and although I can provide indirect forms of evidence about what causes sleep-talking, it is very much left to scientists to further explore disorders of arousal and explore their causes in more detail.

Inqusitive Tortoise

Image Credits:

Header Image: Sleep Troubles

Leave a comment

Filed under Uncategorized

How Much Sleep Do We Need?


Despite our urge to squeeze everything out of the day, sleep is something we cannot live without.

As I start to think about this question, I can feel the inner scientist in me asking a range of questions in response to your first. Sadly, I have a limit to how long my response should be before people start turning off… So, to prevent his becoming a short thesis in itself (or several), I have opted to approach this question in terms of a healthy adult and to focus on how much sleep we need to remain physically and mentally healthy, and not just simply survive.

It is important to ask how much sleep we really need, and just as important to make sure we actually try to achieve this. As we’ll see, sleep is vital for the healthy functioning of many physiological and mental faculties that to skimp on it is inexcusable. As I type this, I can hear many crying out “modern living”, “deadlines”, “fitting everything in”, and even the faint whispers of “YOLO” on the breeze. However, sleep is not simply an inconvenience to our daily lives but an important part of keeping us functioning.

To highlight this, let’s look at the effects of a lack of sleep. A chronic lack of sleep has been shown to be associated with heart disease, type 2 diabetes, and stroke to name but a few. It should also be noted that there’s such a thing as ‘too much’ of a good thing, as excess sleep is associated with similar problems as too little sleep (Shen et al., 2016). At some point, you have probably felt the effects of lying in for too long and the scourge of ‘sleep hangovers’.

How do we measure an ‘optimum’?

There are a number of ways we can do this, but first we need to understand what we mean by optimum and why we sleep in the first place. The exact function of sleep is still not fully understood but it is generally agreed that sleep enables us to grow, is vital for memory and keeps us alert and healthy. In fact, prolonged durations without sleep can distort our perception of reality, interfere with our memory in a staggering way and, in very extreme cases, lead to death.

By looking at this in the long-term, we can identify the ‘optimum’ amount of sleep by observing lots and people’s sleep habits and to identify the risks associated with differing hours of sleep. We can also deprive individuals of sleep and see how they function after a couple of hours (or complete) sleep restriction compared to a normal night. For example, if we deprive someone of 1 or 2 hours sleep per night do we see any effect of an individual’s ability to function during the daytime? If the answer is yes, then this would suggest that those extra hours of sleep are important to us in some way.

So, we are now more familiar with why we should attempt to get the right amount of sleep, and how to measure the importance of sleep, but how much do we actually need? The simple answer is that 7-8 hours is generally considered to be ideal for the majority of individuals. A recent study highlighted that 7 hours was optimum for avoiding the negative impacts of too little or too much sleep (Shen et al., 2016). Another comprehensive review highlighted again that between 7-8 hours was optimum when considering all-cause mortality (i.e. your chance of death is reduced if you get between 7-8 hours of sleep a night, when compared to more or less sleep).

What about those who can survive with less than 7 hours?

However, although there is some merit in this claim, it has created the idea that there is a ‘perfect’ amount of sleep, and that this is the same for everyone. This really is not the case and the amount of sleep an individual ultimately needs to feel refreshed and to function varies from person to person. To many sleep scientists this is source of frustration and avid fascination. Take, for example, individuals who only need 5-6 hours of sleep a night to function, and those who claim they can get by with even less.

Why might it be that some people need less sleep than others? The simple answer seems to be that it all lies in our genetics, and certain mutations in our genetic code are linked to a greater resistance to the effects of sleep deprivation. A particular set of gene mutations outlined by Pellegrino and colleagues (2014) was associated with a reduced need for sleep and fewer negative effects associated with reduced sleep (6 hours). They established that a reduced need for sleep, or an increased resistance to sleep loss, is heritable and the genes involved seem to impact the internal clocks we have in every one of cells.


“Sleep is not simply an inconvenience to our daily lives but an important part of keeping us functioning.”

Yet, there is a problem with these studies, and others which have looked at those resistant to sleep deprivation. Some individuals may be resistant to effects of sleep deprivation on attention and day-to-day functioning, but most of the large sleep studies have focused on the health impacts of sub-par sleep over very long periods of time. These ‘sleep-deprivation resistant’ studies are conducted over the course of a couple of weeks; the long-term impact of sleeping less than 7-8 hours, and being resistant to short term sleep restriction, has not be extensively studied.

Therefore, it is conceivable that individuals can go with less than 7-8 hours’ sleep in the short term, and some may be better than others at getting away with this. However, ‘getting away with it’ may be just the term we want to use here. These individuals may be able to compensate early on but still be prone to the same health issues associated with reduced sleep as the rest of us in the long term.

Effect of Chronotype

I am about to go off a seemingly unrelated tangent but bear with me (it’ll be interesting, promise!) When people think and talk about sleep in terms of what is optimum and healthy, they will often focus on the duration of sleep. Most people will also mention when they drop off and wake up, but a large part of this conversation will be in relation to their willpower and how they “should really go to bed earlier and wake up earlier”. However, when we go to sleep is an important factor to keep in mind as we look at what healthy sleep looks like. Each of us can be classified on the basis of something called a chronotype and this describes at what time we go to sleep and wake up on a typical day. Although people fall along a complete spectrum, and show some variability, there are two main camps which most tend to fall into: early risers and night-owls. As the names suggest, early risers go to bed earlier and wake up earlier than the night-owls who find themselves more productive later in the day and subsequently wake up later. Great, thanks for the information Jack, but why is this important for my further understanding of healthy sleep?

Although sleep duration is important for a healthy mind and body, the time at which our body wants us to sleep and rise will impact on whether we can achieve the right amount of sleep in the first place. Our current schooling and working world favours the early-risers. As a result, night-owls unfortunately have to constrain their normal sleeping patterns during the working week to fit with the demands of a 9-5 society. This is important, as night-owls may catch-up slightly on their sleep schedules during the weekend but this is rarely enough and produces what is known as social jet-lag. This is the mismatch between what our body-clocks are screaming at us during the week when we wake up earlier than we would naturally do so, and the extended sleep we have during the weekend to attempt to rectify this.

The attempt to rectify the sleep-debt during the weekend is not enough, and this is highlighted by the increased prevalence of mental illnesses in those who score as night-owls on chronotype measures. Therefore, when as well the duration of sleep is important when we consider what healthy sleep should look like. Granted, altering the duration of sleep might be simpler to achieve for most of us than being able to get up later, but that does not make ignoring our own sleep rhythms any less important.

So, although I could likely go on for much longer, I should leave it there. The take home message is that 7-8 hours is the ideal duration of sleep required for a healthy existence. We should also be mindful that duration is not the only indicator of healthy sleep, and listening to your own sleep rhythms is important to ensure you get sufficient and good quality sleep.


So,  I have to admit that the inspiration for this question came not from me directly. In fact, the question was part of a project which is collecting an increasingly large database of questions about science in general. The project, known as The Science Room, is run by a good friend of mine in Southampton, and it is determined to answer everyone’s science questions (ambitious, I know!) On that note, if you’re interested in asking any science based questions or learning more about the project, you can find the current webpage here: http://thearthousesouthampton.org/the-science-room/

The answer to this particular question is due to appear on a website dedicated to answering all of these questions (amongst many other things!) I shall link that site here when it’s complete.

Inquisitive Tortoise

Image Credits:

Header Image: Exhaustion

Second Image: Clock

1 Comment

Filed under Media, PhD, Psychology, Sleep Science

BBC’s ‘In the Mind’ Series


I haven’t written anything in a little while but hopefully that should be fixed over the next week (workload depending). Anyway, this brief post is a slight departure from the normal foray in sleep and everything related to it. I wanted to bring people’s attention to the series of mental health documentaries, short films and portrayals of serious mental illnesses been shown on the BBC over this month. You can find a summary of all of the programs which have already been aired, and are yet to be aired here: http://www.bbc.co.uk/mediacentre/latestnews/2016/in-the-mind

The hour long documentaries / films follow people who have suffered from mental illness in some form of another and create a narrative for the viewer to follow. The aim is to educate and through this hopefully reduce the stigma surrounding in general.

It’s great to see that these documentaries have tackled issues which receive less attention in the media such as postpartum psychosis and bipolar disorder. The former is a disorder which I frequently come across in my reading but which I had no real understanding of. Although an hour is hardly enough to really get to grips with how these disease manifest and impact on a wide variety of different peoples’ lives, the documentaries on biplolar disorder and postpartum psychosis do provide us a privileged window into the lives of people, and their loved ones, fighting with mental illness. Admittedly, it is hard to watch certain scenes and it personally brings back familiar experiences from my own family, both as a child and as an adult.

Also, if anyone is interested, Prof. Richard Bentall has given his own opinion on the BBC’s depiction of bipolar disorder as primarily a biological disorder (https://blogs.canterbury.ac.uk/discursive/all-in-the-brain/#.VscA52Zud_U.twitter) He acknowledges the role of drugs in the recovery of very ill individuals but argues that a focus on the biological aspect of mental illness does very little to help with stigma (e.g. it creates a dichotomy of the sick and the healthy). I agree in the sense that the documentaries I have managed to watch so far focus on the severe stages of mental illness and neglect the broad spectrum of mental illness from health to hospitalisation. They give people a glimpse into mental health but perhaps see it as if through a window into the ‘other side’. However, I would also argue that these documentaries give understanding of what it means to be given a diagnosis of a mental illness and how individuals and their families deal with this. In this sense, they help to break down boundaries between stigmatised terms, such as ‘psychosis’, with no human experience to attach to them. It is because of this I would suggest people watch at least one of the documentaries being shown and currently on iPlayer.

Anyway, I just wanted this to be brief and not a matter of me typing lots of stuff into the ether of wordpress. One last thing, I also want to give a link to a really useful link about the role of drawing in talking and dealing with mental health (here http://www.bbc.co.uk/newsbeat/article/35564616/mental-health-week-how-drawings-on-social-media-are-changing-the-conversation?ocid=socialflow_facebook&ns_mchannel=social&ns_campaign=bbcnews&ns_source=facebook) Although her work isn’t included here but I personally found the drawings of Allie Brosh particularly helpful and a good explanation of what it is to live with depression (http://hyperboleandahalf.blogspot.co.uk/2011/10/adventures-in-depression.html). Please check some of these out, and share them with people who might find them helpful, educational, or simply interesting.

Inquisitive Tortoise

Leave a comment

Filed under Media, Psychology, Schizophrenia, Voice Hearing

Sleep Snippet: Why Bother Even Trying to Understand Sleep?


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

Image Credits:

Header Image: Sleep in Society

Leave a comment

Filed under General Interest, PhD, Psychology, Sleep Science

Upcoming Articles

While trying to decide what article I’d like to write next I realised that I haven’t really introduced people to the basics of sleep science and why people like me get money to research it. I’ve already used terms which are familiar to most people, but there’s also been some which are probably less so. Hopefully, I’ve explained what these terms are in sufficient detail so far, yet I still think it makes sense to take a step back and examine why we sleep, how we measure it, and why its worth researching in the first place.

I will initially post these articles in a small, bit-sized, format so that they remain informative but also interesting. I’ll likely expand on these in the future, but their size should serve the purpose for the time being.

Thank you to everyone who has read and enjoyed these articles so far btw. These articles have really helped with my own research, and I hope they continue to interest you all!

Inquisitive Tortoise

Leave a comment

Filed under Uncategorized