Category: Sleep and dreaming

Our bodies fail to adjust to seasonal clock changes

The UK and other countries have been altering their clocks with the seasons since at least the beginning of the last century.

The argument in favour of Daylight Saving Time (DST), or British Summer Time as it’s called in the UK, is clear: daylight hours are effectively shifted from the early morning to the evening, so that there is more time for sport and leisure in the summer months.

Increasingly, however, there have been calls for Britain to remain on British Summer Time throughout the year – to stay coordinated with Europe, and to reduce energy consumption in the dark winter months. Now Thomas Kantermann and colleagues have added to the debate with a study showing that the ability of our bodies to acclimatise to the natural changes in sunrise onset is lost following the artificial shift of the clocks forward each Spring.

Kantermann’s team took advantage of self-report data from more than 55,000 people gathered as part of the Munich Chronotype Questionnaire. This showed that the timing of people’s sleeping and waking tracks the natural changes to dawn time that occur during the Winter months (i.e. during standard time) but fails to show the same adjustment after the introduction of Daylight Saving Time in the Spring.

In another study, the researchers used actimeters (gadgets strapped to the wrist that measure movement) to track the sleep patterns of 55 volunteers for four weeks prior to, and four weeks after, the clock changes in the Autumn and Spring of 2006-2007. Again, this confirmed that after the advancement of clocks in the Spring, people’s sleep patterns failed to adjust to the seasonal shifting of sunrise, as they had been doing before the clock change. This was especially the case for ‘owls’ – people with a preference for the evening who find it difficult to get up in the morning.

These results reflect the way people suffer more from jet leg when travelling westwards and time is advanced, compared with travelling eastwards, ‘backwards’ in time.

Co-author Till Roenneberg said: “It is much too early to say whether DST has a serious long-term impact on health, but our results indicate that we should consider this seriously and do a lot more research on the phenomenon.”
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Kantermann, T., Juda, M., Merrow, M. & Roenneberg, T. (2007). The human circadian clock’s seasonal adjustment is disrupted by daylight saving time. Current Biology, 17, 1996-2000.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Students: it’s time to ditch the pre-exam all-nighter

Lack of sleep impairs the human brain’s ability to store new information in memory, researchers have found. Past research has already shown that sleep is vital for consolidating recently-learned material but now Matthew Walker and colleagues have shown that sleep prior to learning is just as important.

“The implications of our findings have never been more relevant than in the present day, when sleep hygiene and total sleep time are declining across all age ranges”, the researchers said, pointing to the “all-nighter” before exams as the “quintessential example” of how we deliberately deprive ourselves of sleep.

The researchers scanned the brains of 28 participants who attempted to remember a series of pictures of people, landscapes, scenes and objects. Half the participants had slept the previous night as usual and acted as controls; the other participants had been kept awake, meaning they’d gone about 36 hours without sleep (the learning task was in the evening). Two days later, after everyone had two nights of normal sleep, the participants were shown more pictures and asked to identify those they’d been shown earlier in the week. Compared with the controls, the previously sleep deprived participants recognised 19 per cent fewer pictures.

Brain scans taken at the time the participants learned the pictures provided some clues as to how sleep deprivation had affected learning-related activity in the brain. Compared with the controls, the sleep deprived participants showed less activity in the hippocampus, the brain area associated with the laying down of episodic memories. Moreover, whereas the hippocampi of the controls was functionally connected with the frontal and parietal lobes, in the sleep deprived participants it was connected with basic alertness networks in the brain-stem – what the researchers said was “potentially a cooperative mechanism attempting to elevate levels of alertness during memory encoding”.

Why does lack of sleep have this effect on memory? The researchers aren’t sure, but it’s possible that lack of sleep denies the brain the opportunity to transfer episodic memories in the hippocampus into long term storage, so that the capacity of the hippocampus effectively becomes filled the longer we’re awake.
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Jyoo, S-S., Hu, P.T., Gujar, N., Jolesz, F.A. & Walker, M.P. (2007). A deficit in the ability to form new human memories without sleep. Nature Neuroscience, Advance Online Publication.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Link to related Digest item.

Electric stimulation boosts beneficial effect of sleep on memory

Having a nap is a great way to consolidate your memory for what you’ve just learned. Now it appears researchers have found a way to boost this beneficial effect.

A control condition confirmed the benefits of sleep: 13 participants remembered 37.42 words in a memory task before sleep, compared with 39.5 on waking. On another occasion with a different set of words, Jan Born and colleagues applied an oscillating electrical current through the participants’ skulls just as they were entering a period of slumber known as slow wave sleep. In this case the participants recalled an average of 36.5 words before sleep, compared with 41.27 words when they were tested on waking – a larger benefit than in the control condition.

“This improvement in retention following stimulation is striking considering that most subjects were medical students, who were highly trained in memorising facts and already performed well in the sham [control] condition”, the researchers said.

During slow wave sleep, populations of neurons oscillate between activity and rest, and the application of an oscillating electric current at this time seemed to accentuate the process. The stimulation also caused more sleep spindles – these are bursts of activity that the researchers said could have led to a strengthening of the synaptic connections involved in memory.

Crucially, the stimulation didn’t boost the participants’ memory when it was given at a different frequency or at a different time (just before waking). It also didn’t help participants to learn patterns of finger movements. Such a task depends on procedural memory as opposed to the declarative memory tested by the word task. “Our results indicate that slow oscillations have a causal role in consolidating hippocampus-dependent memories during sleep”, the researchers said.
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Marshall, L., Helgadottir, H., Molle, M. & Born, J. (2006). Boosting slow oscillations during sleep potentiates memory. Nature, DOI: 10.1038/nature05278.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Compose new music? In your dreams

The source of professional musicians’ creativity could lie in their dreams, report Piero Salzarulo and colleagues at the University of Florence.

They asked 35 professional musicians and 30 non-musical students to complete a record of their dreams and musical activity for 30 days. Over that period, the musicians, who either played an instrument or sang for a living, experienced twice as many dreams featuring music compared with the students (40 vs. 18 per cent of nights).

And 28 per cent of the time, the music that featured in the musicians’ dreams was an original piece. “The occurrence of unknown musical pieces shows that new musical productions could be created in dreams”, the researchers said.

You might say it’s obvious for musicians to dream about music because we often expect the content of our dreams to reflect our waking activities. But actually, past research has shown more complex activities like reading, writing or calculating seldom occur in dreams. The researchers surmised: “This could be an additional argument for the difference between music and the other cognitive skills”.

And moreover, in this study, the likelihood of dreaming of music was not linked to hours of musical activity on the previous day. Instead, frequency of musical dreams was associated with the age at which the musician began their musical instruction. “This finding is in agreement with the notion that the early years of childhood are crucial for establishing the lifelong development of musical skills”, the researchers said.
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Uga, V., Lemut, M.C., Zampi, C., Zilli, I. & Salzarulo, P. (2006). Music in dreams. Consciousness and Cognition, 15, 351-357.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Not such a bad night’s sleep

Photo by MaliasFrom ‘The Archives’, first published in the Digest 2/2/2004

For the 33 percent of Americans who suffer from insomnia, a good night’s sleep is no more than a dream. Part of the their problem could be that they overestimate how long it takes them to get to sleep, thus sustaining a self-perpetuating cycle of sleep-related anxiety.

Nicole Yang and Alison Harvey (Oxford University) recruited 40 students with primary insomnia from two Oxford universities. All the participants said that for at least a month they had suffered difficulty sleeping as frequently as three nights per week.

The participants were kitted out with a watch-like gadget – an actigraph – that provided an objective measure of sleep, based on how much they tossed and turned in the night. For three nights they wore the gadget and kept a sleep diary. Afterwards, half of the participants were shown, based on the actigraph’s measurements, how they had overestimated in their diary how long it took them to get to sleep. The procedure was then repeated for a further three nights.

For the second three-night session, the participants who had seen the discrepancy between their own and the actigraph’s measure of how long they took to drift off, now estimated this period more accurately and reported significantly less sleep-related anxiety than did the other participants.

“The findings support the proposal that distorted perception of sleep functions to maintain insomnia by fuelling anxiety and preoccupation with sleep” the authors claimed. And use of an actigraph “provides a non-intrusive, easy to administer method” of correcting these distortions.
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Tang, N.K.Y. & Harvey, A.G. (2004). Correcting distorted perception of sleep in insomnia: a novel behavioural experiment? Behaviour Research and Therapy, 42, 27-39.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Dreaming of the war

Don’t mention this at the World Cup, but interviews conducted in the year 2000 revealed 17.3 per cent of German people who lived through the Second World War were still experiencing war-related dreams 55 years after it ended.

Michael Schredl and Edgar Piel interviewed representative samples of thousands of people in 1956, 1970, 1981 and 2000 about the content of their dreams. Participants had to indicate whether their dreams featured any of 20 different themes, among which were included four war-related themes – air raid, war captivity, war-zone exposure, and being on the run, as well as more mundane themes such as travelling and work.

Overall, war-related dreams were far rarer in the year 2000 than in 1956, except among people aged over 60, 17.5 per cent of whom still had war-related dreams, a level comparable to the 1956 average across all age groups of 19.9 per cent. In contrast, in 2000, just 8.6 per cent of interviewees aged between 18 and 29 reported having war-related dreams.

“The present study clearly indicates that World War II had a strong and lasting effect on the people visible in their war-related dreams at night”, the researchers said. “The findings are consistent with the ‘generational hypothesis’…i.e. political events or changes have their strongest effect on persons when experienced in late adolescence and early adulthood and when experienced directly”, they said.

Schredl and Piel said their study showed how “…eliciting and analysing dreams is an informative approach to study the effects of political events on the inner lives of people”, and that it added to earlier research such as that carried out among war Veterans showing nightmare frequency was correlated with time endured in concentration camp captivity.
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Schredl, M. & Piel, E. (2006). War-related dream themes in Germany from 1956 to 2000. Political Psychology, 27, 299-307.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Disturbing memories caused by disturbed sleep?

Contributed by Lucy Rowe at Totton College.

Whether it’s possible for memories of a traumatic experience to be forgotten, only to be recovered years later remains controversial. One concern is that people who report experiencing fragments of buried memories of childhood sexual abuse are actually misinterpreting episodes of sleep paralysis. Sleep paralysis occurs when a person wakes from dream sleep before their ability to move their body has kicked in again. Also, their dream can often overlap with their awakening perception of the ‘real’ world, leading to a sense of an intruder being in the room, for example, or the hearing of strange noises. Richard McNally and Susan Clancy from Harvard University investigated whether sleep paralysis is more prevalent among people who have reported recovered memories of having been abused, or among people who believe they’ve been abused but have no memories of it.

After advertising for participants in a newspaper, McNally and Clancy gave sleep paralysis questionnaires to 18 people (17 women) who believed they had been sexually abused but had no memories of it, 14 people (8 women) who had ‘recovered’ at least one memory of being abused, and 36 people (28 women) who reported being abused and never having forgotten the experience. Only 8 of these participants were able to provide an external source to corroborate their abuse claims. Sixteen people (11 women) who denied ever having been abused, served as a control.

Sleep paralysis was indeed more prevalent among the participants who reported having been abused (around 45 per cent experienced it) compared with the control group (only 13 per cent had). Although when asked to choose an explanation for their sleep paralysis, only one woman (from the recovered memory group) related it to child abuse.

Explaining their findings, the researchers said “Individuals who have unusual sleep-related experiences tend to score high on measures of absorption and dissociation, and people reporting sexual abuse histories also score high on these measures”.
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McNally, J.R. & Clancy, S.A. (2005). Sleep paralysis in adults reporting repressed, recovered, or continuous memories of childhood sexual abuse. Journal of Anxiety Disorders, 19, 595-602.

You’re feeling very sleepy

Just thinking that they’ve not had much sleep could interfere with the daytime functioning of imsomniacs, regardless of whether they actually had enough sleep or not.

Twenty-two students (average age 21 years) with primary insomnia were recruited by Christina Semler and Allison Harvey at Oxford University. All had experienced at least three nights’ sleep disturbance per week for the past month.

For three nights, the students’ sleep was measured using a sensitive gadget that records how much its wearer moves around. Each morning, an electronic display that the students thought was connected to this gadget, told them how well they had slept. But in fact the display was controlled by the researchers, so that they could trick the students into thinking they’d had a good or bad night’s sleep, regardless of how well they’d actually slept.

On days that the students were led to believe they’d had a poor night’s sleep, they reported having more negative thoughts (e.g. “I can’t cope today”), feeling more sleepy, performing more sleep-related monitoring (e.g. noticing aching muscles/ sore eyes), and resorting to more compensatory behaviours (e.g. taking a daytime nap). That’s despite the fact that the actual quality of their sleep didn’t vary significantly between days they were given positive or negative feedback about their sleep.

Together with past research showing imsomniacs often sleep much better than they realise, these findings suggest it could be their anxiety about not sleeping well, rather than a lack of sleep per se, that causes or worsens the daytime impairments so often reported by imsomniacs.

If these results can be replicated with a clinical sample, the authors said, then “…consideration should be given to teaching insomnia patients to lend less credence to their subjective perception of sleep. And the adverse consequences, for daytime functioning, of concluding that they’ve not obtained enough sleep should be emphasised”.
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Semler, C.N. & Harvey, A.G. (2005). Misperception of sleep can adversely affect daytime functioning in insomnia. Behaviour Research and Therapy, 43, 843-856.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.