Category Archives: Sleep Science

Should We Start Drinking Cherry Juice To Improve Our Sleep?

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Should you start drinking cherry juice to boost your sleep?

The internet is awash with advice based on rubbish science, and it’s not unusual for news outlet to pick up on this. Luckily, I have a source who expertly scours the internet and provides me with the best of the worst scientific journalism. Today’s offering is from the Daily Mail who are advertising the miraculous sleep inducing powers of tart cherry juice and other shady sleep treatments. The article in question claims that you can get 84 extra minutes of sleep if you start drinking tart cherry juice. Seems too good to be true? Well, let’s take a look at the research in question.

This study was led by Jack Losso at Louisiana State University. His team had a group of 8 people take part in a pilot trial of whether tart cherry juice would improve sleep in a group of individuals diagnosed with insomnia. The participants in this trial were initially randomised to either drink a cherry or placebo drink twice a day (once in the morning and once again a few hours before bed). Their sleep was assessed at the start of the study and again two weeks later at the end of each stint of juice or placebo. They found that the participants spent 86 more minutes asleep in the cherry juice compared to placebo condition. Additionally, out of five self-report sleep measures there was found to be an increase in sleep efficiency (time in bed divided by time spent asleep) as measured by only one of these.

Unfortunately, this study is not available online, so we only have access to the abstract and the press release until it is published September 2018. This makes it hard to analyse in any more detail. This was a very small pilot study with only 8 participants diagnosed with insomnia. In addition, the study threw a lot of different sleep questionnaires at the trial for little plausible reason other than they could. It’s not unusual for there to be two (different measures assess slightly different things) but five is overkill. This is worrying as it suggests that the researchers could change the goal posts if one measure did not produce the effect they wanted to see.

The Daily Mail articles also seems to have glossed over the age of the participants who were “over 50” according to the study. This study alone is not enough to convince us that cherry juice is something we should all stock up on to combat a poor night’s sleep. However, what is the wider evidence to support cherry juice impact on sleep?

The initial rationale for conducting these trials was based on a mixture of anecdotal evidence and plausible biological pathways. For example, it has been suggested that tart cherry juice can reduce inflammation and increase melatonin levels. Both of these could conceivably improve an individual’s sleep. However, prior to this recent pilot trial there was very little scientific research to support an association between improved sleep and tart cherry juice. Based on my own search of the literature, there were two additional published trials I could find which looked at the effect of tart cherry juice on sleep.

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The evidence for cherry juice and sleep is currently lacking

The first by Glyn Howatson and colleagues recruited a sample of 20 people with a mean age of 27. In this study participants were either given diluted tart cherry juice or a placebo fruit cordial. The participants were not told about the hypotheses beforehand, but I’m still not entirely convinced that people wouldn’t have cottoned on to what drink was supposed to be doing something. The researchers found no differences in sleep when they looked at the self-report measures except a reduction in napping from 9 minutes to 2 minutes in the cherry juice group. Participants in the cherry group did stay in bed slightly longer and spent longer asleep (34 minutes) as measured by a Fit-Bit like watch. Of course, if they were spending longer in bed, immobile, it is perhaps not surprising that their sleep would have been longer too due to limitations of such devices (e.g. they treat a lack of movement as sleep).

The second study by Wilfred Pigeon and colleagues conducted another pilot randomised controlled trial with 15 people who were, on average, about 72 years old. It used a similar setup as Glyn Howatson’s randomised controlled trial in that participants were randomly assigned to drink either the placebo or cherry juice first. The other drink was then given two weeks later. Their ‘cherry juice’ was actually a blend including both tart cherries and apple juice which makes it hard to say that it was the cherry juice specifically having the active effect. In this study, using self-report sleep diaries, it was found that participants went to sleep 2.6 minutes quicker, slept 8.4 minutes longer, and spent 17 less minutes awake during the night in the juice (cherry and apple) compared to the placebo juice drink. A fuller exploration of this study can be found here on the brilliant NHS Choices website but again, this study is far from convincing.

Together, these studies are not poorly conducted but their findings are not particularly impressive either. They do suggest that cherry juice may be doing something but it’s hardly comparable to the supposed 84 minutes which leads the Daily Mail article. In fact, the second study, besides having a tiny effect on sleep, is not even solely cherry juice. Personally, I don’t have the option to get 85 extra minutes sleep, I’m more interested in my sleep being more restful. None of these studies showed that this was the case and this is something which is likely to be more important to most people including those with a diagnosis of insomnia.

Finally, because you can’t make this kind of stuff up, two of these three studies were part or fully funded by the Cherry Marketing Institute. The only study that wasn’t funded by them was given free products by a company which produces and sells, including other products, cherry-based drinks aimed at physical enhancement. It’s not unusual for an intervention to have a hand in a trial but this, and the Daily Mail article, feels more like advertising than validating a potential treatment. Is it too much to ask for a randomised controlled trial without some form of cherry PR company hovering in the background?

With all of this in mind, cherry juice’s effect on sleep does not seem to have a scientific basis. As always, if you find tart cherry juice is a miracle cure for you then feel free to ignore me. Your glass of tart cherry juice is hardly causing anyone harm and it’s fantastic if, anecdotally, it works for you. However, in this instance, it looks like cherries are another alternative treatment for insomnia which need to be taken with a considerable bucket full of salt.

I never liked cherries anyway.

Inquisitive Tortoise

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References

Losso, J. N., Finley, J. W., Karki, N., Liu, A. G., Prudente, A., Tipton, R., … & Greenway, F. L. (2017). Pilot Study of the Tart Cherry Juice for the Treatment of Insomnia and Investigation of Mechanisms. American journal of therapeutics.

Howatson, G., Bell, P. G., Tallent, J., Middleton, B., McHugh, M. P., & Ellis, J. (2012). Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. European journal of nutrition51(8), 909-916.

Pigeon, W. R., Carr, M., Gorman, C., & Perlis, M. L. (2010). Effects of a tart cherry juice beverage on the sleep of older adults with insomnia: a pilot study. Journal of medicinal food13(3), 579-583.

 

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Biphasic Sleep: Should we stop sleeping in a single, uninterrupted, block?

 

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“What’s the right amount of sleep I need? Should I be drinking cherry juice to sleep better? Why do you keep ignoring my voicemails?”

In the absence of being asked about dreams, people are generally keen to hear my views on how to get the best sleep possible. I think this is a fair question to ask a sleep scientist. I’m less convinced that you’ll get an accurate answer from a mattress salesman – but maybe that’s just me. A normal night’s sleep typically involves a single block from the moment our heads hit the pillow to when we feel our way towards our phone alarm in the morning. The number of hours sleep will vary but this will probably be somewhere between 7 to 9 hours (it may be slightly more or less than this). Hopefully, you’ll also feel fairly refreshed after waking up. Many of us still feel tired the following day for a myriad of reasons and will seek some solution for how to feel more energetic, creative and productive. One sleep buzzword which has attracted many such sleep perfectionists is ‘biphasic sleep’ and it involves splitting up our usual undisturbed bout of sleep.

For some people, sleep is experienced as two (or more) bouts of slumber throughout a night. For these biphasic sleepers, they will enjoy an initial sleep followed by a period of wakefulness and then finish off the night with their second sleep. Unlike those of us who restlessly wake up in the middle of the night and feel awful the following day, biphasic sleepers feel fully refreshed with their fragmented pattern. Some natural biphasic sleepers can even mistake their wakefulness for insomnia and this can cause its own problems.

There is some evidence that biphasic sleep is everyone’s normal sleep patterns but artificial lighting has forced us to sleep in one undisturbed bout. However, the scientific evidence to back this up has been somewhat sluggish. It wasn’t until late into the 20th century that our capacity for a biphasic sleep schedule was brought to light.

In the early 1990s, the psychiatrist Thomas Wehr showed that individuals under strict lighting conditions shifted from a single block of sleep to sleeping in a more segmented fashion. In his sample of eight healthy white men, Wehr had them spend 4 weeks under ‘winter’ lighting conditions whereby they had 10 hours of light a day. Then, as a comparison condition, the participants were exposed to 16 hours light and 8 hours dark to broadly mimic summer lighting for a single week. Under summer lighting conditions, the participants slept in one single block and appeared to be largely consistent in their sleeping patterns. However, when they were required to spend a month in the winter lighting pattern, they showed fragmented sleep that was typically, but not always, split in two or more segments (e.g. biphasic). This suggests that provided the period of darkness is long enough, such as experienced during the winter months, then the sleep period will start to be split up over a typical night. As a result, advocates of biphasic sleep as the optimum sleep schedule frequently quote this study as concrete evidence for their point of view.

It’s important to note a few things about this commonly referenced study. In the ‘winter’ condition, participants were told they could do not do anything active during the dark periods (e.g. listen to music or exercise). They were not allowed to use artificial lighting and were encouraged to rest during the dark period. This didn’t leave much choice but to sleep during this 14-hour window. Therefore, biphasic sleep might be seen because the participants had nothing better to do than go back to sleep if it was still dark upon awakening.

This was the same conclusion put forward by a study published in 2015 which also argued that a switch to biphasic sleep may simply be a result of long winter nights. Not everyone agrees so readily with this interpretation. However, until more convincing research is forthcoming it looks like we shouldn’t be trying to wake ourselves up at 2am every morning for that mid-sleep conference call. There is no evidence (as always please try to prove me wrong) that splitting your sleep into two segments is better than sleeping in a single block. Current advocates of biphasic sleep tend to singularly use Wehr’s study as evidence for their points without acknowledging the caveats to his study.

So, that still leaves the question remaining why some groups are advocating splitting up your sleep into small segments if the evidence is lacking. Well, besides our obsession with being told exactly how much of everything (e.g. fruit, water, sleep, fun) we are supposed to have there is a common theme to those keen to split up their sleep – they want to sleep less. Madness, I know.

Terms such as biphasic and polyphasic are frequently kidnapped against their will to lend legitimacy to schedules such as Everyman and Uberman schedules. These sleep schedules aim to break the day into small naps so that people can work unhindered by something as trivial as sleep. To put this into context, the Uberman schedule involves sleeping no more than 2 hours broken neatly up into 6 separate 20-minute naps – sounds lovely, doesn’t it? Well… By contrast, the Everyman schedule allows you 3 hours of sleep followed by 3 naps of 20 minutes throughout the day. So, you get a whole 4 hours sleep with this approach. I will save why these schedules are ridiculous for another post, but I’ve included them to illustrate that interest in segmenting the night’s sleep overlaps considerably with ‘hacking’ the numbers of hours of sleep we need in a day.

As I’ve hopefully make clear so far, sleep is important – all of it. Hacking your sleep will leave you exhausted and at an increased risk for multiple physical and mental illnesses. If you’re interested in feeling more energetic, perhaps think about whether sleep really is the culprit. Alternatively, maybe stop reading these blog posts at 2am and sleep. Actually, on second thoughts…

Inquisitive Tortoise

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References

WEHR, T. A. (1991). The durations of human melatonin secretion and sleep respond to changes in daylength (photoperiod). The Journal of Clinical Endocrinology & Metabolism73(6), 1276-1280.

Ekirch, A. R. (2016). Segmented sleep in preindustrial societies. Sleep29 (3), 715-716.

Yetish, G., Kaplan, H., Gurven, M., Wood, B., Pontzer, H., Manger, P. R., … & Siegel, J. M. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology25(21), 2862-2868.

 

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Why we should be logging off from social media well before bedtime

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Photo @BrickinNick

So I am trying to experiment with shorter style articles a little bit. For those lovely people out there reading this, any feedback you have on this short pieces would be much loved! 

It is a fact universally acknowledged that a single man in possession of a smartphone must be in want of all of the notifications. I think that’s how that saying goes anyway…

It should come as no surprise that social media use is far from ideal for our mental health. It is an addictive and impulsive activity which can leave us constantly checking for any activity on our posts or feeds. It’s also a force for good but there is the need to understand where its use becomes pathological. For example, a study (poll) published earlier this year linked the usage of social media platforms such as Instagram to poorer mental health outcomes. It would be unfair to claim that social media can solely be blamed for mental health difficulties facing adolescents, but it is equally naïve to suggest it plays no part. How does sleep come into this equation then? Well, besides the sleep-interfering influence of the blue light emitted from devices to browse social media, it appears its usage can mess with our ability to drift off peacefully at night.

A recent study published last month by researchers at the University of Pittsburgh addressed this exact question: is social media usage before bed predictive of disturbed sleep? More specifically, they examined whether habitual social media usage in the 30 minutes before bed would interfere with the sleep of a large sample of American participants (n=1736). The researchers asked participants to report on their level of sleep disturbance over the 7 days and based on this they were identified as either having low, medium or high sleep disturbance. The participants’ social media usage before bed was rated as: rarely or very rarely, sometimes, often or very often. This was asked in respect to the past year.

So, what did the researchers find? Well, perhaps unsurprisingly, they found that social media usage 30 minutes prior to bed was predictive of poorer sleep. This was still the case when overall social media usage was controlled for which suggests that targeting social media usage before bed might be a useful strategy to improve sleep in habitual users. Interestingly, this research supports a well conducted study published last year in the Journal of Adolescence which also corroborates the role of night-time social media use on sleep quality.

However, why do we need to be careful about these findings? Well there are a number of issues I can think of which take away from this study. For example, a validated measure of sleep loss would have been more informative than the broad categories used to identify sleep disturbance in this study. Admittedly, the authors do highlight this in the discussion section of the paper too. Furthermore, the use of social media usage before bed in the last year is something which I imagine would fluctuate considerably. To me, it makes more sense to ask about social media usage in the past week if your sleep measure is concerned with this time-frame too. The best way to do this would be to track social media usage and sleep daily. You could not say that one causes the other with this approach but it would be more informative. Finally, it is unclear from this study whether social media usage before bed was responsible for the sleep disturbance. Poor sleep could be responsible for the increased social media use before bed or there might be some other variable entirely which explains both increased social media usage before bed and the disturbed sleep.

Of course, this work should not be surprising to any one of us and it makes reasoned sense that using a device just before bed is likely to interrupt with your ability to sleep properly. I think the merit of this paper is that it reminds us that perhaps a blanket ban on social media is not needed. If social media usage can be curtailed when we should be doing more important things (e.g. sleeping) then perhaps this can start to reduce the negative impact it has on our mental health. As with all research this is just a tiny part of a much bigger picture but it is an issue which will only increase – not decrease any time soon.

Until that future research is forthcoming, avoid endlessly scrolling for likes before bed if you want to be on peak witty tweet form the next day. Or, you know, you just want to feel less tired. Either is fine.

Inquisitive Tortoise

References

Levenson, J. C., Shensa, A., Sidani, J. E., Colditz, J. B., & Primack, B. A. (2017). Social Media Use Before Bed and Sleep Disturbance Among Young Adults in the United States: A Nationally Representative Study. Sleep, zsx113.

Woods, H. C., & Scott, H. (2016). # Sleepyteens: social media use in adolescence is associated with poor sleep quality, anxiety, depression and low self-esteem. Journal of adolescence51, 41-49.

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Twitter, chronobiology, Trump, and Questions You Didn’t Realise Needed Answering

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Tweets in their natural environment

Scientists are a weird bunch. We spend our lives getting very excited about niche and bizarre things. As a result we have a habit of spending our free time trying to get others to understand our excitement. There are also times when these strange topics align with the wider interests of the general population. For example, we may ask the big questions which are important and crucial for a functioning society.  However, there are also times when we wonder whether we can put to bed (pun fully intended) whether Donald Trump is a keyboard bashing night-owl or a keyboard bashing early riser. But you don’t want to know about that, right?

Well in case you do, luckily one rather eminent (and fun) chronobiologist felt that it was appropriate to answer that singularly important question. Don’t worry, we’ll come to why this is actually an important question later. Now, social media can be used to identify a lot about us and it is not that hard to use all of the data from platforms such as Facebook to track (loosely) a friend’s sleep. It also seems that social media can also be used to determine your activity patterns and assess biological rhythms besides sleep.

For anyone who has ever logged onto Twitter, you are probably aware of the late-night tweets of @realDonaldTrump and their varying levels of coherence. However, do these few late-night tweet fests correlate with the normal chronotype of the president? Firstly, what do we mean by chronotype? Chronotype is the term used to refer the times at which individuals tend to be awake and active. For example, you are probably familiar with the concept of morning and evening types. These relate to our internal body clocks and govern whether we are happy to work late or decide to retire early on. Although society seems to associate the early birds with success, there are issues when our body clocks do not align with the pressures of a society which is regimented and requires us to wake up at the set times – whether for work or school. In fact, there is growing and convincing evidence to suggest that delaying school start to fit with adolescent’s chronotype would be beneficial .

Typically, we assess chronotype through the use of questionnaires or by tracking activity of an individual over an extended period of time. Yet, how can we assess Trump’s chronotype if we can’t handily give him a detailed questionnaire or activity tracker? Simple, we mine his Twitter data and assess his activity based on tweets. Luckily for us, the current President likes to tweet – a lot. This gives interested researchers plenty of time points to assess how his activity changes over time.

Professor Roennenberg applied his analysis to 12,000 tweets from December 2014 to March 2017. Out of all these tweets, there were three main devices they were sent from: an android device, an iPhone device, and other miscellaneous devices. The majority of the tweets were from the android device and it was suggested that the android phone was likely Trump’s personal phone. With all of this rich data, it was possible to identify the peak tweeting periods and how these changed month by month over the 830 days of tweets analysed.

So, what was found? Well, contrary to expectations, it appears that Trump is actually a consistent morning type. There was a clear patterning in the peak times at which he was tweeting. There tended to be a peak in the morning between 5:10am-9:40am (around sunrise) and a peak in the evening 5:00pm-11:00pm (around sunset) that shifted through the year with the change in hours of sunlight. For example, during the summer months, Trump had peaks of tweets earlier in the day and during the winter months these were later during the day. This is a clear pattern of tweeting which fits seasonal changes in light levels.

By contrast, tweets sent from the iPhone showed peaks of activity between 8am and 4pm which highlights a mixture of working hours and staff activity. It was hard to assess circadian patterning using this account as it appeared that multiple people contributed to these data. The ‘MiscDevices’ showed peak activity during between 8.20am and 4.50pm which suggested that this was used during the working day. On the basis of this, the study showed that it is possible determine patterning of activity over a long period of time from tweet data alone. In this case, it shows the peak tweet activity for Donald Trump and in turn this allows us to determine (roughly) his chronotype and probable sleep period.

Why is this worth reporting on? Honestly, to begin with, it is hilarious. I love the author of this piece for taking a ridiculous question and applying the full force of the scientific process to it. Personally, I think this research should be considered for an IgNoble award. However, when you move past the fun of this piece it also highlights a powerful research tool. The use of social media data in research is increasing and there are some great and novel studies which have taken this approach. This method can allow us to, as in this paper, track the sleep, circadian and seasonality patterns of an account – provided it has sufficient data points. In this case, Trump was a perfect proof of concept. Moreover, this technique could also be used to not just track sleep patterns but also be mined for content. Roennenberg makes a quick allusion to the content of Trump’s early morning tweets but this approach has implications for research. This data mining of social media approach would enable questions to be asked not just about the patterning of account activity but also how this activity might be associated with, for example, mental health. To me this is an exciting tool which has considerable potential albeit with significant ethical concerns attached.

Until then we can use this technique to open a window into the life of the rather prolific tweeter that is Donald Trump. Now don’t tell me science isn’t tackling the big (so big) questions.

Inquisitive Tortoise

References

Roenneberg, T. (2017). Twitter as a means to study temporal behaviour. Current Biology27(17), R830-R832.

Berry, N., Lobban, F., Belousov, M., Emsley, R., Nenadic, G., & Bucci, S. (2017). # WhyWeTweetMH: Understanding Why People Use Twitter to Discuss Mental Health Problems. Journal of medical Internet research19(4).

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Do Insects Need Sleep?

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Anyone with even the slightest fear of creepy crawlies has probably been in the following situation. You settle down for the evening and quick as a flash you see a behemoth of a spider run out. It dashes underneath the sofa before you can react, and, your night ruined, you are left waiting for it to kill you. After a while you’ll convince yourself that it has probably gone to sleep and, seeing as it’s 2am, you should too. However, did it go to sleep? Do insects sleep at all?

One of the many questions which I get when I tell people that I study sleep is some variant of: do insects sleep? What is the smallest creature that sleeps? Do you sleep? Well let’s delve into the world of the mini-beasts to find out the answer to that first one.

Many insects such as bees, moths, cockroaches, and butterflies (to name but a few) will show behaviours that seem indicative of sleep: relative immobility, increased arousal threshold (e.g. harder to wake them up), and drooping antennae. Insects don’t have eyelids so they can’t get “shut-eye” in the usual sense but these other behaviours look a lot like sleep. However, is this really sleeping? Some have argued that the pattern of inactivity shown by some insects can be better referred to as torpor. This is like sleep but torpor involves enhancing the survival of the organism during times of limited resources or when in a harsh environment (e.g. low temperatures during winter). Torpor is often compared to hibernation in mammals and referred to as a ‘mini hibernation’. Unlike sleep, torpor is regulated by external factors rather than an internal clock as in humans and other mammals. However, if what we see is simply torpor in insects then we would not expect them to experience difficulties in functioning after sleep deprivation. So, do insects show signs of poor functioning if they don’t sleep even during normal environmental conditions?

The science suggests that they do.

For example, fruit flies show patterns of inactivity remarkably similar to human sleep – they show recovery sleep, struggle with vigilance and performance after not getting enough rest, and show a steady rhythm of wake and sleep. One well researched example of the effects of sleep loss on bugs can be seen in honey bees. As they mature into foragers for a hive they move from near constant activity to strongly structured patterns of activity and rest as they hunt for food. However, when foragers are not able to sleep they show difficulties in successfully carrying out vital tasks – for example, dancing. For bees, dancing is a vitally important skill (honestly). While away from the hive bees can communicate with one another through a display known as the ‘waggle dance’. This figure of eight movement, interspersed with a slight waggle, is meant to tell other bees about the distance and direction of food sources, pollen, and the hive. Now, how exactly do you deprive a bee of sleep without interfering with its daily schedule? I’m glad you asked. You use something aptly named the ‘Insominator’.

Yes, really.

This fantastically named device is a beautiful example of the awful sense of humour scientists possess. The device was developed with the express purpose of ensuring that bees were sleep deprived in an automatic manner while still being part of their hive. Like humans, research should try not to interfere with the daily schedule of participants (no matter how many legs they have) so we can be more confident it was the thing we’re interested in, and manipulated in some way, which is responsible for the effects observed. Despite its funny name, it was actually a pretty cool piece of kit and allowed the bees to go about their social activities (bees are rather social) whilst only disrupting their sleep.

In the study led by Prof. Bennett Klein, they compared the performance of bees’ waggle dance before and following sleep deprivation. Interestingly, when the bees were kept awake they were less able to effectively carry out the waggle dance and alert other bees to resources. More specifically, the bees were less accurate in conveying direction information to other bees and this in turn, it is predicted, would negatively impact foraging behaviour of other bees in the hive. As is seen in other social creatures, and me without a strong coffee or five, sleep deprivation impaired communication skills of these honey bees. Although the mechanisms are more complex in humans it suggests that certain insects do sleep and that this can have a negative impact on social functioning. Although the jury is still out as to whether the rest shown by many insects constitutes sleep, the effects of a lack of this inactivity seem to mimic the effects seen in humans. At this point, I’ll let you make the decision whether we can call this sleep or not. Alternatively, if you have any ideas on how to study whether an insect sleeps, please send your answers in on a postcard addressed to Jack and marked ‘SCIENCE’.

So, if anyone asks you whether insects sleep you can go forth and spread the unclear, slightly contentious, word. Alternatively, you can just remember that bees dance, scientists have a terrible sense of humour, and that the spider still underneath your sofa is asleep. Probably. In fact, it’s probably best just to seal off that room.

Inquisitive Tortoise

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References:

Klein, B. A., Klein, A., Wray, M. K., Mueller, U. G., & Seeley, T. D. (2010). Sleep deprivation impairs precision of waggle dance signaling in honey bees. Proceedings of the National Academy of Sciences107(52), 22705-22709.

 

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Can sleep loss induce a negative implicit bias towards Arab-Muslim names?

Racism

People suck. Well they certainly seem to after several nights without sleep. As the lost hours pile up, those simple things sent to try us become all the more difficult to face. We are generally just less able to employ self-control to moderate our feelings towards the outside world. I mean, it’s like Nigel Farage said to me down the pub once, we even tend to make racist comments when we’re a bit tired. Now sleep deprivation does not make you racist, despite amusing attempts to throw old Nige a bone, but it may be that a lack of shut-eye can make us less able to inhibit unconscious biases.

Unconscious biases are not necessarily a bad thing before we start to bash them. They allow us to employ speedy decision making without having to weigh up the pros and cons of a situation. When you’re faced with immediate danger you don’t want to spend time considering the difficult childhood of your knife wielding assailant for any more than a split second before you run away with your tail, and wallet, trailing behind. However, when we’re not facing a troubled mugger your conscious mind can step in and make use of available mental resources to stop yourself acting on your unconscious biases. This allows you to mask your own biases under the shield of social desirability. However, how do you assess an individual’s unconscious biases if they are unaware of them themselves?

It is possible to assess your unconscious biases by completing something called the implicit association test (IAT). This was developed by social psychologists Anthony Greenwald who wanted to try to understand the unconscious biases individuals held. They felt that explicitly asking individuals about sensitive issues was a poor way to investigate controversial topics as people would be likely to hide their true responses behind a ‘socially desirable mask’. Instead if you got people to respond very quickly to words paired with negative or positive emotions you could see how readily certain associations are recognised. For example, you could show pictures of white and black faces and pair them with positive and negative emotions. You could then present every possible combination in a randomised order (black-good, white-bad; black-bad, white-good) and see how quickly people respond to these pairings. The logic being that if you were quicker to respond to black-bad and white-good than the other pairings you, on an unconscious level, see these as more strongly related than the alternatives. Race is used here as an example but this task has been used for a wide range of different judgements such as gender and careers, weight, age and many others. You can see many of them and give the task a go here.

It should come as no surprise that sleep is considered important when it comes to our unconscious biases. Hopefully anyone who has read at least one of these posts should be aware of how many things sleep is important for. A study published in 2015 showed that by stimulating slow wave sleep (i.e. the deepest stage of our nightly slumber) you could enhance daytime training to reduce unconscious negative biases. However, it was still relatively unknown how sleep loss could influence our own hidden biases. This is not just an interesting question but an important one too when you consider that implicit biases can negatively guide our behaviour outside of our awareness.

Therefore, in a paper published last month a team from Harvard University explored this question and wanted to understand whether chronic sleep deprivation could lead to an ‘unmasking’ of negative implicit biases. More specifically, they asked: Are we more likely to express an implicit negative bias towards Muslim Arab names when we are sleep deprived?

To test this question, seventeen participants were invited into the laboratory for 25 days and it was under these strictly controlled walls that participants’ sleep was monitored. During this period, invited participants spent five days on 4 hours sleep and two days on 8 hours. This continued for a total of three weeks. The same participants, were invited back 2 months later to spend another three weeks in the laboratory but this time they could sleep for 8 hours every night. This meant that each participant served as their own control for the study. On the 21st day participants were given the implicit association test (IAT) for Muslim-Arab names and the scores during the well-rested and sleep-deprivation conditions were compared. The researchers predicted that during sleep deprivation participants would show an increased negative implicit bias towards Muslim-Arab names (i.e. they would be less able to mask their biases).

So, what did they find?

Well when participants were well-rested they did not show a negative implicit bias towards Muslim-Arab names. This is good and somewhat encouraging. However, when they were sleep deprived the same participants did show significant evidence of a negative implicit bias. That is, they more readily associated Muslim-Arab names with “bad” rather than “good”. This suggests that sleep deprivation may make us more likely to express our implicit biases.

Well before we get carried away this task is not a perfect way to assess unconscious biases and simply because our perceptions are unconsciously altered does not mean our behaviour is too. It’s also important to note that this group of participants did not have an implicit negative bias normally (e.g. when well-rested). Yet, it was possible to see that a moderate bias was found following three weeks of substantial sleep deprivation. On that note, it would be very interesting to see if in groups who already have an implicit bias show the same increase in bias following sleep deprivation and whether good sleep could reduce the negative implicit bias shown.

However, it does suggest that sleep deprivation in situations where workers have to act quickly and intuitively may bias our perceptions in a negative, and potentially fatal, way. This is particularly relevant for police officers, military personnel, and individuals working in airport security who may work long shifts and who may need to make snap judgements. We should be careful before anyone shouts from the rooftops “being sleepy makes you more racist”. This task is looking at implicit biases and the IAT do not represent explicit biases. In most instances we have the time, and resources, to make a balanced judgement. Nonetheless this research showed that a lack of sleep can negatively influence our own unconscious biases towards others. As for outright racism? A lack of sleep won’t suddenly make you racist – sorry Nige.

Image Credits:

Header

References:

Alkozei, A., Killgore, W. D., Smith, R., Dailey, N. S., Bajaj, S., & Haack, M. (2017). Chronic Sleep Restriction Increases Negative Implicit Attitudes Toward Arab Muslims. Scientific Reports7.

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Filed under Politics, Psychology, Racism, Sleep Science

Have you considered sleep with that? How global warming may stop us getting a good night’s sleep

Insomnia and Heat

When we think about increasing global temperatures we tend to think melting ice caps, flooding, and conspiracy theorists who believe scientists (or the Chinese) make this stuff up to exert some unknown power and influence. However, the temperature at night has a direct influence on the quality of our sleep too. So, I’m back to talking about sleep again (the sigh of relief from my adoring crowd is audible – thank you). A recent paper, published in Science, has shown that global warming will not just have an effect on political alliances but also on our sleep. Trump, take note.

The premise of the recent paper, by Dr Nick Obradovich and colleagues, is a simple but profound one. As the summer months trundle on by (and yes, we get some occasional sunshine here in the UK too) you are probably acutely aware of the nightly sojourn to bed and futile attempts at sleep in the oppressive heat. Unless you have the advantage of a trusty fan or even a hint of a breeze outside you know you are going to toss, turn, and throw the covers around until you eventually nod off for a few fragmented hours. Temperature has an evident ability on our ability to get to sleep. This is shown clearly when we consider the changes in body temperature throughout a typical night. As we drift off our body temperature reduces and remains lowered during the sleep period until we wake up. At this point, it starts to rise again helping to improve alertness during the day. This pattern, or circadian rhythm, is no accident – it helps to send us off to sleep. This rise and fall is important and if we increase our temperature too much (e.g. lying in a particularly stuffy room) then we delay the time at which we drop off and are more likely to wake up during the night.

It is this quirk that a research group explored in relation to global warming. In light of what we know, will the increase in global temperature negatively influence our sleep? We can assess this by looking at unseasonably hot days during a month and correlate this with the reported number of nights of poor sleep in the population. This is exactly what Obradovich and colleagues did. They assessed the temperature changes from the average in a number of cities across the US and identified the sleep habits of hundreds of thousands of respondents to a large survey assessing health and disease. They controlled for potential confounders and found that as the temperature increased from the average, for any given month, that there was an increase in reports of nights with disturbed sleep. In fact, as the temperature rises then so does the number of disturbed nights of sleep. When the group compared low and high earners and young and old populations they found that those who were poorer and older tended to suffer more from the effects of temperatures spikes. Finally, as would be expected, they found that these effects were only significant when they looked at the summer months.

This highlighted largely what we already know: that temperature negatively impacts on sleep quality by interfering with the normal process of drifting to sleep. However, the interesting point comes from the next finding of their study. They identified the predicted increases in global temperature until the end of the century from NASA. They then plugged in these values from the first part of the study to identify the effect of increasing temperatures of the number of nights sleep loss until the end of the century. Somewhat worryingly, they found that over the next century the number of nights poor sleep increases in line with the increases in temperature in part due to global warming and climate change. This has implication for physical and mental health which has consistently been tied to the quality and duration of our sleep.

It is important to note that there are plenty of caveats to this study. For example, its indirect and correlational measure of sleep and temperature should raise some concerns about the validity of the findings. Furthermore, it’s important to note that sleep was assessed with a single self-report question, “During the past 30 days, for about how many days have you felt you did not get enough rest or sleep?”. As the authors suggest, further experimental data is needed to back up their claims.  However, the findings from this study do fall in line with what we already know about the effect of temperature on sleep. It is not a stretch to claim that global warming, ignoring other external factors, will have a negative impact on our sleep. There are of course ways to mitigate the negative effects of increasing global temperature but this study also accounted for that. The poorest and oldest stand to suffer most as they cannot afford to keep air conditioning running all night. Therefore, although this is one admittedly large-scale study there is still additional research which needs to further understand the true impact our warming climate will have on our sleep and subsequent health. For the time being, it raises an important reminder that the effects of global warming are far reaching and ignoring the clear evidence for its existent is nothing short of irresponsible and short-sighted. Again, take note Mr. President.

Image Credit:

Header

References:

Obradovich, N., Migliorini, R., Mednick, S. C., & Fowler, J. H. (2017). Nighttime temperature and human sleep loss in a changing climate. Science Advances, 3(5), e1601555.

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Filed under Media, Politics, Psychology, Sleep Science, Work and Society

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).

stages-of-sleep2

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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Filed under General Interest, Memory, Psychology, Sleep Science

How Might Escaping Technology Help Improve Our Sleep Problems?

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“Won’t someone please think of the children?!”

Besides infancy, we don’t initially think of sleep as a big problem in childhood. Yet, a slew of recent articles have highlighted that insomnia and other sleep problems are not simply an issue of adulthood. A BBC Panorama documentary released last week commented on the surge in problems with sleep in children. Although there were a number of culprits identified for this increase in the problems with children’s sleep, one key point was technology and later exposure to artificial light.

We are all glued to our smartphones, laptops, and Fitbits. Modern artificial lighting allows us to work and entertain ourselves further into the night than natural light permits but the normality surrounding their use before bed is negatively influencing sleep. As people are educated more about the effects of technology on sleep, these issues should hopefully reduce but whether education can effect this change is uncertain. The question remains: How can we improve sleep without dragging people away from technology? One love-it or hate-it option may be camping.

Last month, a research group led by Kenneth Wright carried out two studies which examined how artificial light interferes with our natural sleep rhythms and our body’s concept of day and night. Study one assessed the sleep of participants firstly during artificial lighting and then natural lighting during the winter. The second study attempted to understand the impact of weekend camping on sleep. The researchers studied sleep by asking them to wear a watch to track movements and by tracking changes in a hormone called melatonin. Melatonin is released prior to sleep, reaches a midpoint during the first half of sleep and dips as you wake up. During the day, it is only detectable at trace levels because in the presence of light melatonin’s production is inhibited. This, in part, explains why we feel tired and want to go to bed at night rather than during the day. As a result, melatonin serves as a useful and precise marker of the internal biological night (i.e. when the body feels we should be sleeping).

The first study had participants spend a week, during winter, camping with no artificial light (e.g. torches or phones) and then a week in their normal, modern, environment which served as a baseline. Participants’ melatonin levels were measured during sleep after about 6 days of the modern environment and after 6 days of the natural light, camping, condition.

This initial study found that the internal biological night (e.g. melatonin onset, midpoint, and offset) is affected by seasonal fluctuations. Specifically, internal biological night is longer during winter and shorter during the summer. In the camping condition, melatonin onset and sleep onset were around 2 hours earlier compared to the modern, artificially lit, condition. However, melatonin offset and sleep offset were similar between camping and baseline. When comparing the winter data to previously collected summer data, the melatonin onset was earlier and melatonin offset was significantly later in the winter condition. More specifically, they showed a four-hour difference in internal biological night between winter and summer. However, there were no change in internal biological night between summer and winter offset when comparing the artificial light conditions. The modern, artificially lit, environment had extinguished the seasonal fluctuations in melatonin and sleep patterns.

The second study then went on to assess whether weekend exposure to natural light (i.e. camping) could help reduce the effects of social jet lag – the mismatch between the time you wake up during the weekday and weekend. We tend to delay our sleep during the weekend and this contributes to why it is so hard to wake up on a Monday morning. In this study, fourteen participants were first tested in their normal, artificially lit, environment and their melatonin levels during the night (onset, midpoint and offset) were assessed. Participants were then separated to a camping condition (n=9; natural light) or normal condition (n=5; artificial light).

What did they find? For the camping condition, the time at which participants went to sleep and woke up were similar between weekday and weekend. However, for the artificial light condition the onset of sleep was found to be delayed by almost 2 hours and participants woke up around an hour and a half later during the weekend compared to the weekday. People were staying up later and waking up later during the weekend presumably when they didn’t have work. Overall sleep duration and efficiency were similar across and within both groups. So, participants were not sleeping for longer under artificial light but were delaying their sleep schedule.

What about the data for internal biological night? In the camping condition, melatonin onset and midpoint were about an hour earlier during the weekend compared to weekday despite there being no changes in sleep timing. Interestingly, changes in melatonin were not only seen in the camping condition but also the modern setting. Melatonin onset, midpoint and offset were delayed by about an hour compared to the weekday for the modern, artificial light, condition. This is problematic if you have to get up earlier on the Monday morning for work and is linked to what we know as social jet lag. If you feel sleepier later and want to wake up later then you may find yourself being groggy and sleep deprived during the week.

Yet, when participants went camping over the weekend, they did not see a shift in their sleep onset or offset, and their biological night became advanced (started earlier) slightly. This suggests that weekend exposure to natural light (e.g. camping) may help diminish the negative effects of living in the current, high-paced, environment we currently have. The small sample size and short sampling period makes it hard to draw definite conclusions from this study but it does highlight that artificial lighting is having a definable impact on our sleep and the biochemistry underpinning it. It also provides some preliminary evidence of the biological impact of social jet lag.

You may, quite rightly, think that the results of this study are rather obvious: we stay up later during the weekend and our biology is going to follow suit unless we hike out to the middle of nowhere for the weekend. However, it highlighted the biological impact of our modern, well-lit, environment on our body’s internal clock. We know that using our devices before bed are generally bad for sleep but very few of us actually do anything about this. We may try to adopt better bedtime habits but this may be thwarted by technology (e.g. using a kindle to read just before bed)

Also, it is key to remember that light is not the only regulator of our sleep rhythms and in societies not exposed to artificial light the key determinant of the sleep cycle is temperature. This should make us think about not a single factor (i.e. light) but a multitude of issues may cause issues with our sleep. Interestingly, such individuals in cultures not exposed to artificial light also reported problems with insomnia but at a reduced rate than reported in modern society.

Nonetheless, light from devices, rich in low-wavelength blue-light, resets our biological clocks and inhibits the release of melatonin. As a result, we feel sleepier later even though we still have to get up at the same time and go to school, college or work. The recurrent sleep deprivation can in turn lower our mood, concentration and put us at increased risk of illness and metabolic disorders. Now, it is unlikely that the rise of childhood sleep problems can be fixed by wrenching tablets from children and throwing them out into the wilderness every Friday until Sunday. Nonetheless, we can think about what these devices are doing to our sleep – at the very least when we’re sleeping poorly to begin with.

Inquisitive Tortoise

 

ResearchBlogging.orgStothard ER, McHill AW, Depner CM, Birks BR, Moehlman TM, Ritchie HK, Guzzetti JR, Chinoy ED, LeBourgeois MK, Axelsson J, & Wright KP Jr (2017). Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend. Current biology : CB, 27 (4), 508-513 PMID: 28162893

 

Additional References:

Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232-1237.

Yetish, G., Kaplan, H., Gurven, M., Wood, B., Pontzer, H., Manger, P. R., … & Siegel, J. M. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology, 25(21), 2862-2868.

 

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Filed under Sleep Science, Technology, Work and Society

Sleep’s Positive Impact on Traumatic Memories

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Sleep is inescapable. Some will see it as a necessary evil and others will claw at it with limited success. It may leave us (largely) immobile but it is anything but a passive state. Sleep paves the way for new neural connections to be made, clears the brain of harmful waste products, is protective against mental and physical illness, and is preferable to leaving the bed on a cold Monday morning. There is still plenty of debate as to the true function of sleep, but one key area which it appears to be important for is memory.

Broadly speaking, it is argued that sleep enhances the consolidation of recently learned information compared to wakefulness. For example, a nap as short as 5-10 minutes has been shown to enhance memory and improve problem solving compared to wakefulness following learning. Moreover, rapid eye movement sleep has been linked to enhanced memory for emotional information, and to reducing the emotional strength of such memories. This suggests that different aspects of sleep are important for different types of memories and highlights some potential ways we can modify the impact of negative ones. What if we could interfere with the brain’s ability to form negative memories? More specifically, what if we could interfere with traumatic and intrusive memories which form the basis of illnesses such as post-traumatic stress disorder (PTSD)? Recent research seems to suggest this may be possible.

PTSD is a psychiatric disorder characterised by flashbacks and nightmares, avoidance of the situation in which the trauma occurred, and emotional numbing. It is the result of a traumatic event which can be wide in scope (e.g. warfare, sexual abuse, hospital admission) and individuals with PTSD will often find themselves transported back to the event. These ‘memories’ are intrusive in nature and, understandably, highly distressing. It has been suggested that interfering with the consolidation of intrusive memories at the time they are formed (or shortly afterwards) may help those who are likely to go on to experience PTSD. Evidence to support this would unlock a powerful early intervention tool for those likely to experience trauma (e.g. refugees or soldiers). One way this can be achieved, as you have likely guessed, is through manipulating sleep.

In 2015, a study conducted at the University of Oxford explored whether sleep deprivation might be protective against intrusive traumatic memories. Participants were brought into the laboratory and randomised to either a sleep deprivation or sleep group. They were then shown a film containing traumatic scenes which lasted just over 15 minutes. Following the film, participants were either kept awake or allowed to sleep. On the following day, participants completed a questionnaire measure of PTSD symptomology and were then asked to complete a diary to track the intrusiveness, content, distress, and presence of mental imagery associated with the traumatic film for 6 days.

The Oxford group, led by Dr. Kate Porcheret, found that a night of sleep deprivation, compared to sleep as normal, reduced the intrusiveness of experimental-trauma memories. The sleep deprivation group reported fewer intrusive memories, lower PTSD symptoms scores, and (non-significantly) reduced distress of the intrusive memories. However, this effect was only found for the first two days and sleep deprivation was found to confer no protection against intrusive memories after 6 days. This suggests that sleep deprivation immediately after the traumatic experience can reduce its intrusiveness but only in the short term. Sorted. Sleep deprivation, paradoxically, confers some protective against traumatic memories. Right? Well, to quote Ben Goldacre, “I think you’ll find it’s a bit more complicated than that”.

A study published last December in the aptly named journal SLEEP has injected additional complexity to this issue. Dr. Birgit Kleim and colleagues assessed the impact of a single night of sleep deprivation on distress and intrusiveness of traumatic memories for seven, rather than six, days. They asked 65 female participants to watch two 12 minute films of a neutral (nature documentary) or traumatic (horror film) nature in a randomised order. Participants were either allowed to sleep at home or kept awake. They were then asked to keep an intrusion diary which required participants to note when they experienced intrusive memories related to the film and rate their vividness, intrusiveness, content, and distress each day. The participants were then followed-up a week later.

So, what did they find? For the first two days following the films, there was no significant difference between the sleep or wake groups on distress or intrusiveness of the traumatic film. However, by days 6 and 7 there was a significant reduction in distress and intrusiveness for the sleep compared to wake group. By contrast, there were no difference in intrusiveness or distress of the neutral film for the sleep and wake groups. The effects found were specific for the traumatic, emotional, memory.

This second study showed that sleep deprivation does not provide a protective effect against intrusive emotional memories. Instead, they argued that sleep immediately following the trauma experience has long-term benefits on reducing the distress and intrusions associated with the traumatic memory. Nonetheless, this study does not directly contradict the one conducted by Porcheret and colleagues at Oxford. Although non-significant, distress was higher for the sleep compared to sleep deprivation group which suggests that sleep deprivation may serve an immediate protective role against traumatic memories. However, this effect seems to reverse in the relative long-term.

Why should this be so? Well, we know that memories – particularly emotional ones – are strengthened by a period of sleep. This would suggest that sleep following a traumatic experience would strengthen the memory for that experience and thus enhance the intrusiveness of a traumatic memory. This could explain why sleep deprivation produced a reduction in intrusiveness and distress for the Oxford study as the lack of sleep interfered with the ability to lay down the negative memory. However, the explanation for these studies is less clear. The authors argue that sleep deprivation is protective against intrusive memories in the short term but not the long-term. Kleim and colleagues claim that sleep following the traumatic experience may initially make it more distressing but also encourage appropriate integration of the memory alongside existing memories. This, they argue, reduces the chance that the traumatic memory will be intrusive and uncontrollable – a cardinal symptom of PTSD.

We already know that rapid eye movement sleep (REM) is associated with a reduction in the intensity of emotional images (van der Helm et al., 2011). Kleim’s study found that increased REM was associated with more, not less, intrusions. Instead, they argue that other stages of sleep are responsible for the reduction in distress and intrusions seen perhaps through a different mechanism. However, this does not state that the memory should be remembered more poorly (i.e. deliberate recall of the film would be unaffected). Rather it seems that deliberate memory recall and intrusive memories may be guided by different mechanisms and differentially affected by sleep. Neither the Porcheret or Kleim study asked participants to take a memory test of their explicit recall of the films. However, the diary studies suggest that all participants were accurate in recalling the films throughout the study period and deliberate recall does not appear to be associated with intrusive memory frequency.

tetris

A similar distinction between intrusive and deliberate recall of memories was found by another study attempting to reduce the negative impact of traumatic memories. Indeed, these are the not the first studies which have attempted to interfere with the consolidation of traumatic memories. A more colourful way of achieving this has been shown through getting people to play Tetris. For the uninitiated, Tetris is a simple game whereby you match coloured bricks of different shapes into lines of 4. They fall from the top of the screen and you have to rotate the shapes to make them line-up and disappear. In 2009, Dr Emily Holmes and colleagues at the University of Oxford showed that if they got participants to play Tetris for 10 minutes, half an hour after a traumatic film, they saw a reduction in subsequent intrusions or “flashbacks”. This effect was found for over a week follow-up during which an intrusion diary was kept. Interestingly, deliberate recall of the film was not impaired when tested at one-week follow-up. This also suggests it is possible to reduce the intrusive nature of a traumatic memory without reducing the memory for the event.

Of course, it is difficult to get someone in a warzone to take out their Tetris ration or take a nap following a fire-fight, but it highlights that it is possible to reduce the negative impact of traumatic memories. These pieces of research suggest that manipulating sleep is a viable way to reduce the ‘flashback’ quality of traumatic memories. Although promoting sleep for those having recently experienced a traumatic episode might raise its own difficulties, it heralds a step towards early intervention for PTSD. If nothing else, they remind us that sleep is important for the consolidation of memory alongside existing memory networks and how little we know about the effect of sleep on memory.

One thing we do know for sure: sleep is anything but a passive and simple state.

Inquisitive Tortoise

References:

Holmes, E. A., James, E. L., Coode-Bate, T., & Deeprose, C. (2009). Can playing the computer game “Tetris” reduce the build-up of flashbacks for trauma? A proposal from cognitive science. PloS one, 4(1), e4153.

Kleim, B., Wysokowsky, J., Schmid, N., Seifritz, E., & Rasch, B. (2016). Effects of Sleep After Experimental Trauma on Intrusive Emotional Memories. Sleep.

Porcheret, K., Holmes, E. A., Goodwin, G. M., Foster, R. G., & Wulff, K. (2015). Psychological effect of an analogue traumatic event reduced by sleep deprivation. SLEEP, 38(7).

van der Helm, E., Yao, J., Dutt, S., Rao, V., Saletin, J. M., & Walker, M. P. (2011). REM sleep depotentiates amygdala activity to previous emotional experiences. Current Biology, 21(23), 2029-2032.

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Bad Memory (Header)

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Filed under Dreaming, Memory, Psychology, Sleep Science, Trauma