Many apps now include this feature, and provide users with a range of outputs from basic sleep structure to specific recommendations about how to improve sleep alongside their behaviour and sleep patterns.  What is concerning though, is that some of these recommendations are not scientifically-based or in line with best practise.  Most of these apps also claim to be extraordinarily accurate in their movement detection and sleep stage interpretation.  These claims are somewhat surprising given that sleep researchers themselves have been using movement as a surrogate for sleep and wake for some time, and not one of us thinks we can accurately interpret sleep stages from that data.  (Believe me, if it was possible, we would use it in a second.)

Activity monitors (actigraphs) are fairly reliable at detecting total sleep time (sleep duration).  Although not quite as accurate, they also provide an acceptable measure of sleep onset latency (the time from lights out to falling asleep) and sleep fragmentation (broken sleep).  Actigraphs are less reliable in clinical populations than in healthy adults.  It is not known whether this reduced accuracy extends to those with sub-clinical sleep difficulties.

Actigraphs cannot reliably measure different sleep stages, and I think this is highly evident in the graphical representations of sleep that many of these apps produce.  Often their sample diagrams show vastly abnormal sleep structure, and slow wave sleep shortly before waking.  If you’re getting a healthy amount of sleep each night, slow wave sleep just prior to waking is extremely unlikely.

Many sleep apps now include a feature to optimise our time of waking, so that we wake from light sleep. This is purported to reduce sleep inertia, which is a sensation of grogginess, confusion and decreased functioning, experienced immediately on waking.  Waking from slow wave sleep is thought to contribute to sleep inertia; however, sleep structure, sleep routine and time of day are also likely to be involved.  However, if we are to assume that sleep stage detection was reliable and given that regularly waking from slow wave sleep would suggest restricted sleep duration, and/or poor sleep routine or timing, I wonder if the focus should be on improving overall sleep health, rather than fixation on alarm clock times.

That said, a few apps provide great advice on healthy sleep, with sensible advice on how to achieve it.  Additionally, many people report benefit from using these apps (for example, waking feeling more refreshed) but I’m inclined to think that this results from a focus on achieving better sleep, and perhaps the effect of receiving personalised feedback on your own sleep, than the performance of the app itself.

Daylight savings time is all about shifting our daylight hours so they align optimally with our working day. The upcoming transition to daylight savings time provides a way of shifting our daylight hours to be one hour later. This transition means that we shift our day/night cycle one hour forward in relation to our internal circadian body clock and therefore, to adjust to the new day/night cycle, we need to shunt our circadian clock one hour back. On Saturday night, we are going to lose an hour out of circadian clock’s day. It’s not going to like it.

Studies have shown that on average, we will get about an hour’s less sleep on Saturday night (that is, we don’t tend to strategically make up for missed sleep on that night). Missing out on sleep will help us get to bed an hour earlier on Sunday night and in fact, our bed times seem to adjust quite quickly after the switch to daylight savings time. Consistent sleep loss certainly helps push bed times earlier.

Unfortunately, our circadian body clocks don’t make such a quick adjustment. Because our circadian clocks influence our sleep/wake timing, our sleep structure changes and we often wake earlier than we’d like in the days following the switch to daylight savings time. You may recall me saying in a previous post that our circadian clock prefers to drift later. This means that it is much easier for us shift to our sleep times later, than earlier. There is some variability between individuals but in general, it takes about a week for our wake times to adjust to the new schedule. There is also some evidence to suggest that the shorter the sleep we usually get, the harder it is for us to adjust.

While it is clear that there are direct effects on sleep and circadian rhythms resulting from the transition to daylight savings time, there is conflicting evidence about the follow-on effects on waking function. Additionally, studies are not always comparable, with varying classification of degrees and type of accident or injury; and different study populations. That said, the transition to daylight savings time may be associated with increased motor vehicle and workplace accidents, as well as decreased productivity.

So what can you do to minimise the impact of the transition to daylight savings time on your sleep and waking function?

1. Try to optimise the amount and quality of your sleep in the days leading into daylight savings. Missing out on sleep means you will cope less well. Follow good sleep habits – get a healthy amount of sleep (7-9 hours) at a healthy time of the day; avoid caffeine, nicotine and excessive alcohol; and optimise your bedroom environment.
2. Try to shift your bed and rise times 15-30 minutes earlier in the days prior to daylight savings.
3. Expose yourself to sunlight in the mornings leading into daylight savings. Open the curtains in the room you are in. Even better, go for a 20-30 minute walk first thing in the morning (but ensure you don’t cut into your sleep time to do this).

Short sleep amongst students is not uncommon. As a teenager, our circadian body clock naturally drifts later. Those late bedtimes and lengthy sleep-ins we see in teenagers are actually a normal physiological phenomenon. Our body clock generally returns to ‘normal’ in our early twenties. However, late bedtimes in teenagers and young adults, coupled with required early rise times due to school and other commitments, often means their sleep is cut short.

Alongside this, our behaviour can sometimes boost these changes in the timing of our circadian body clock. Most university students, at some time or other, have probably worked long hours after uni to pay the rent, worked all night on an assignment you really should have started two weeks ago because it’s due tomorrow, or simply gone out quite late and stayed out really late. Regular late night activity helps reinforce our body clock to later bedtimes and later rise times. More often than not, they lead to short sleep.

So how does short sleep relate to learning? Well, there are a number of studies in this area but a recent study in high school students showed that increased study time outside school was associated with decreased school performance (that is, understanding information in class or doing poorly on a test). However, after further analysis, it became evident that increased study time was associated with poor performance because it cut into sleep time.

This is not to say, of course, that increased study time is not beneficial for learning (there clearly is a relationship), but it does highlight that extending one’s daily activities at the expense of sleep, will likely lead to decreased academic performance the following day.

To date, research has largely focussed on information storage during sleep rather than new information processing during sleep.  For example, we know that the learning of varying types of information is enhanced with sleep, and that different types of information are better learnt during different sleep stages.

However, up until now we haven’t seen many studies that have successfully demonstrated that we might be able to learn new information while we are asleep.  Using very simple forms of associative learning, researchers have previously demonstrated that animals, such as rats, and human infants are able to process some types of information during sleep.  In these studies, the brain centres activated during sleep were the same as those we use when we unconsciously process information (eg, motor skills when learning to ride a bike). 

To date, no studies have successfully shown that we can actively process during sleep information we have learnt consciously (eg, remembering the trip you took at Christmas 2003, knowing that your bright red sweater needs to be washed separately).  However, in a group of young adults, Arzi has shown that we might be able to process this type of information during sleep.

Different tones were played to sleeping adults and each time a particular smell was wafted past their nose.  Particular tones were linked to particular smells – pleasant (deodorant, shampoo) or unpleasant (rotten fish or flesh) – and the sniff response to each measured.  (A strong sniff response is linked to a pleasant smell and a weak response to an unpleasant one.)  The tones were repeated many times during the night and the  researchers were then able to test whether an association had been learnt between the tones and a particular smell.

Arzi and colleagues showed two fairly exciting things.  We seem to be able to learn during our sleep and demonstrate that learning during the same sleep period.  When tones only (no odour) were played in the second half of the night, the matching sniff response was demonstrated.  Information learnt during sleep continues into wakefulness.  When the tones only were played during the following day, the matching sniff response was demonstrated.

This is very much a first step in this area and it will be interesting to see where this study leads.  It is definitely unclear whether more complex learning is possible during sleep, and then if it is, what function or role this type of learning could serve.

Just over 10 years ago, Australian researchers showed that our performance at the end of the day, on a day where we’ve decided to stay up late, was similar to our performance when driving drunk. 

Essentially they compared how we function when given a placebo drink, at different levels of alcohol intoxication, and when we are asked to stay awake for long periods of time.  Not surprisingly, our performance on a range of simple and complex tasks gets worse as our blood alcohol levels (BAC) increase.  However, our performance also gets worse the longer we stay awake.  These individuals woke up at the beginning of their normal day, stayed awake all day and then were asked to stay up through the following night.  All up, they were awake for 28 hours.

It seems our performance stays fairly stable up to 17 hours after we wake (on a usual working day, about 11pm) but after then it steadily declines.  Our ability to do complex tasks, such as driving, decreases much more rapidly than our ability to do something simple like respond to a single visual cue.

They found that our performance after we have been awake for sometime in the range of 17-19 hours is similar to that when we have a BAC of 0.05% (the legal driving limit in many countries).  They also found that our ability to function after we have been awake for about 20 hours (about 2am) (on complex tasks like driving) and about 25 hours (on the simplest tasks), was similar to our performance at a BAC of 0.10% (over the limit in New Zealand).

Something to think about…

Fewer adverse outcomes arise from the transition from DST, than the transition to DST*.  That said, changes in sleep and performance are still experienced.  These fall into two categories: (a) the changes we experience from the shift in the day/night cycle compared to the timing of our own internal body clock, and (b) the effects of our behavioural responses to transitions to and from DST.  This Sunday’s change from DST to Standard Time requires our body clock to shift an hour later**.  This shift is an easier one; our clock likes to drift later anyway.  However, the gradual seasonal changes we experience in the day/night cycle also help this along. 

Winter is a time of short daylight hours and long nights.  As we head out of winter, our daylight hours lengthen.  They extend at both ends of the day, which means to make full use of our daylight hours we would have to be up at 4-5am (simply not sensible for optimal daytime performance).  DST provides a way of shifting our daylight hours to be one hour later.  This transition means we shift our day/night cycle one hour forward in relation to our internal body clock.

Conversely, as we head out of summer and into winter, the days become shorter.  Suddenly, our change to a later day/night cycle means there is less light in the morning, so we opt to shift from DST back to Standard Time.  This gradual shortening of daylight hours, and the drift to a later sunrise, will lend a helping hand in coping with this Sunday’s DST transition.  Those of you who are lucky enough to wake without an alarm clock may have noticed that you have already begun to wake later.  Daylight hours have a profound effect on the timing of our internal body clock and consequently, our sleep.

The change from DST to Standard Time provides an opportunity to catch up on an hour’s sleep.  However, only those who are missing out on sleep will be able to sleep in***.  Catching up on sleep might have a positive effect by reducing sleepiness, and improving your cognitive and motor functioning.  For those of us who don’t want to sleep in, we will need to be aware that we will have a longer waking day than usual (approx. 1-hour longer).  Towards the end of our day, we will become sleepier, our performance will start to decrease and our risk of accidents will increase.

It is thought that behavioural changes may play a large role in the risk of sleepiness (and therefore, accidents) during DST change.  A transition from DST may mean that individuals who usually stay out late on Saturday nights choose to stay out even later.  Individuals may also stay out later on several nights preceding DST change in the knowledge that they will be able to catch up at the weekend.  Another consideration with Sunday’s DST change is the extra hour that needs to be fitted into the work schedule of shift workers.  Extended hours of work may also lead to sleepiness, and increase the risk of accident or injury.  If you have been up for longer than usual, or later than usual, make sure it is safe for you to drive home.

* I will save discussion about the change to DST for later in the year

** Give or take, depending on your recent sleep routine.  Additionally, our endogenous clock time is not 24-hours.

*** A good proportion of us are able to sleep in during DST change, what does this tell us about our sleep habits?

BBC News Magazine: The myth of the eight-hour sleep **

Reading this title, what’s your first thought?  That we don’t need 8-hours sleep, right?  Hands up anyone who thought ‘I knew that I could get away with 6’?

But in fact, this is not what the BBC article reports.  It discusses the concept of biphasic sleep — sleeping in two, approximately 4-hour chunks across the night.  This concept is not a new one.  As the article points out, there are many historical reports of individuals waking for a couple of hours in the middle of the night.  In general, these hours were whiled away with activities such as reading, writing, chatting or intimate relations.  Note, there were no electrical light, TVs or tablets in these historical times.  Bed time was a lot earlier than ours, and the time available for sleep from bed time to final wake time was a lot longer.

I am not particularly knowledgeable of the historical accounts of this phenomenon but it has been studied scientifically.  In the early 1990s, Thomas Wehr investigated the effect of changing the length of daytime light exposure (and conversely, night length) on sleep, and found that with long nights, human sleep occurs in bouts, with periods of quiet wakefulness during the night.  Wehr hypothesised that it was our modern sleep/wake pattern, with considerably and chronically shortened sleep periods, that increased sleep propensity and drove consolidated sleep.  When Wehr gave people a 14-hour sleep opportunity, they had a few days of catch-up sleep (11-hours in total!) followed by sleep in two main bouts, with a period of quiet wakefulness in between.  Each bout lasted about 2-5 hours with the wakefulness period lasting 1-3 hours.  How long did these people sleep in total?  8.25 hours on average.

** If you didn’t think that one was misleading, have a look at this.  I suppose, an exercise in what happens if you rip off another’s news article without reading any of the background material.

During the last few days, my Google reader has been filled with reports of a controversial new brownie (‘Lazy Cakes’) available for sale in the United States.  This latest edition adds to a range of baked goods and/or dietary supplements aimed to promote relaxation and therefore supposedly, sleep.

Sold at supermarkets, and department and convenience stores, Lazy Cakes contain ingredients the manufacturers believe promote relaxation, such as valerian root, rose hips and melatonin.  Although not explicitly cited on the Lazy Cakes website, web commentary has suggested that these products may be used to promote sleep.  Certainly, a New York Times article cites individuals with insomnia who have tried Lazy Cakes.  Much of the web discussion at present has centred on the use of melatonin in these brownies and in particularly, the reasonably high dose of 8mg melatonin per brownie.

There is considerable concern about taking melatonin as a dietary supplement.  Melatonin is a neurohormone that interacts with a number of systems in the body, of which only one is the circadian (body clock) system.  It also has a significant role in the control of our reproductive function, thermoregulation, thyroid function, carbohydrate and lipid metabolism, urine output, immune function… the list goes on.

Many people associate melatonin with a sleep-promoting hormone because it is secreted at night (coincidentally when humans sleep) and suppressed by light during the day.  In fact, melatonin is secreted at night regardless of whether we are diurnal (active during the day) or nocturnal (active at night).  When it comes to sleep/wake information, melatonin’s main role is to tell us what time of day it is.  Melatonin also changes seasonally in all mammals (including humans) so it can also tell mammals what time of year it is, which is important for reproduction and hibernation.

Many studies have considered the influence of melatonin on our sleep timing and quality.  In humans;

• Melatonin’s main action is in its ability to shift the timing of our sleep by changing the timing of our body clock.  This means that taken at the wrong time of the day, melatonin may shift the timing of your sleep to an undesirable time.  Timing instructions do not come on the packets/bottles of melatonin-containing products.  Would you know exactly when you should be administering melatonin to optimise your sleep timing?
• Melatonin has no effect on sleep quantity or quality when used as a sleep aid.
• Timed appropriately, melatonin can shorten the time it takes you to fall asleep but in healthy adults, this effect is usually incredibly small (something like 4 minutes on average; statistically significant but not clinically significant).  It does seem to be more effective at reducing the time it takes to fall asleep in those with insomnia, but it still does not change sleep quantity or quality in this group.
• Acute side effects include, commonly, headache and taken during the active day, sleepiness and fatigue.
• We do not know the long-term risks associated with frequent administration or inappropriate timing of melatonin.  At present, the greatest concern lies with its effect on our reproductive function, including reproductive cancers.

To the general public, melatonin is usually promoted as a product for those who are having trouble sleeping, including those with insomnia.  As someone who is not an advocate for pharmacologic treatment for chronic insomnia, if it were me, would I regularly take dietary supplements containing melatonin to improve my sleep?  Not on your life.

The current gold standard for objectively measuring sleep is called polysomnography or PSG. This mouthful is derived from the Greek poly meaning ‘many’, somnus meaning ‘sleep’ and graphein meaning ‘to write’.  Polysomnography allows us to record a wide range of physiologic signals during a sleep period.  At the simplest level, we will record signals that allow us to stage human sleep, but in addition we often measure signals such as heart rate, breathing (effort and airflow), muscle movement, oxygen saturation, carbon dioxide levels and behaviour (via video input).  Each recorded signal requires a sensor, or several sensors, often making this quite an overwhelming experience for a patient or research participant.

To be able to determine the stage of human sleep, we need to simultaneously measure three particular signals; electroencephalogram (EEG; brain waves), electrooculogram (EOG; eye movements) and electromyogram (EMG; chin muscle tone).  These measurements are taken via Grass gold cup electrodes (although silver chloride may also be used) filled with a conductive paste or gel. To be able to accurately stage sleep, each electrode needs to be placed at a particular site. For example, the EEG is applied according to the International 10-20 electrode placement system.  After the recording is completed, a trained Sleep Physiologist (also known as a Sleep Technologist or Sleep Scientist) visually examines each 30 second epoch of the EEG, EOG, EMG signals, and applies a sleep stage following international rules for sleep staging [1, 2].  This is an incredibly time consuming process that requires a reasonable level of skill.  Unfortunately, no computer can yet accurately see what a Physiologist can with their own eyes.

There are advantages and disadvantages to quantifying sleep in this way.  The discussion is too big for this post but in essence, sleep has been measured this way for most of its (fairly) short existence as a science.  Continuing to do so allows us to put any new research in context.  However, applying static sleep stages in this manner does not take into account the continuous nature of sleep and in addition, brief changes in sleep status are lost with our current method.  Many researchers are now looking at additional ways of analysing brain activity during sleep and I hope to share some of these with you in later posts.

References

1. Iber, C., Ancoli-Israel, S., Chesson, A., & Quan, S. F. (Eds.). (2007). The AASM manual for the scoring of sleep and associated events: Rules, terminology and technical specifications (1st ed.). Westchester, IL: American Academy of Sleep Medicine.
2. Rechtschaffen, A., & Kales, A. (Eds.). (1968). A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Los Angeles, CA: Brain Information Service/Brain Research Institute, University of California.

A bit of sleep history… The concept of sleep stages was first postulated in 1937 by Loomis et al.  This concept went through several iterations in the following decades.  However, it was Aserinky and Kleitman’s groundbreaking discovery of REM sleep in the early 1950s that set us on the path to defining sleep as NREM sleep and REM sleep.  Sleep stages as we currently know them were defined by a committee of sleep researchers, chaired by Allan Rechtschaffen and Anthony Kales in 1968. These criteria have recently been updated by an American Academy of Sleep Medicine committee (2007) to comply with our current understanding of sleep physiology.

Most of us have an understanding that we go through each of the different sleep stages each night but few of us know what our sleep actually looks like.  The answer is complicated as our sleep structure is different on every night, but sleep structure does follow a general pattern.  Let me show you…

The diagram above shows a schematic hypnogram¹ of sleep stages across the sleep period.  A hypnogram is a graphical way of presenting changes in sleep structure.  On the y-axis you will be able to see Stages 1 through 4 sleep and REM sleep.  Stage 1 is the lightest stage of sleep and comprises up to 5% of the sleep period.  Stages 3 and 4 are the deepest stages of sleep.  These are collectively referred to as slow wave sleep², denoting the slow frequency, high amplitude EEG seen during these stages.  Our threshold for arousal is highest during slow wave sleep therefore this stage is also referred to as deep sleep.  Slow wave sleep and REM sleep each comprise approximately 20% of the sleep period in a healthy young adult.  The remainder of our sleep period is made up of Stage 2 sleep, or ‘light’ sleep.

The hypnogram also depicts changes in sleep that occur across the sleep period.  Slow wave sleep predominates in the first half of the night and REM sleep in the latter half.  Transition through all the sleep stages are reasonably cyclical and repeat every 90 minutes, approximately.

Does sleep really look like the schematic version of the hypnogram?  Sort of…

These rapid changes in brain activity also mean it is also quite normal for the brain to return to wakefulness on a frequent basis.  Arousals from sleep are shown in the lowest panel in the hypnogram.  One vertical line represents one brief arousal from sleep.  Arousals are an expected part of normal healthy sleep; in a healthy young adult these arousals typically occur 10-15 times per hour of sleep.  We are not aware of any of these brief arousals as they usually only last a matter of seconds.

No doubt this post has left you with many questions.  I can imagine a few…

Does our sleep change with age?  Yes.  Is there such a thing as ‘too many arousals’?  Yes.  Why is there a difference between the number of arousals and the indication of Wake on the hypnogram?  We’ll have to leave the detailed answers to these questions for another time.  If you have questions, let me know in the comments section and I’ll do my best to address them in future posts.

¹ Hypnogram kindly reproduced with permission from Gander, P. H. (2003). Sleep in the 24-hour society. Lower Hutt, New Zealand: Open Polytechnic of New Zealand.

² The 2007 sleep staging criteria refer to slow wave sleep collectively.  That is, Stages 3 and 4 sleep are no longer defined separately.