Does sleeping face-down induce more sexual dreams?

It's a common experience for us to incorporate sounds we hear while we're sleeping into the narrative of our dreams. The real car alarm outside becomes a police siren in our exciting chase through dreamland. Given the way activities and sensations from the real world permeate our dreams, the author of a new study, Calvin Kai-Ching Yu at Hong Kong Shue Yan University, has investigated whether the simple fact of our sleeping position can also affect the kinds of dreams we're likely to have.

Yu surveyed 670 people (average age 19) - including 227 men and 443 women - about the content of their dreams, their dream intensity, their usual sleeping position (face up, face down, or lying on their side), and their personality.

Yu's main finding is that sleeping more often in a prone (face down) position is associated with a higher prevalence of experiencing particular dream themes, including: being locked up; dreaming about hand tools; sexual experiences; being smothered and unable to breath; swimming; and being nude. Although sleeping more often in a prone position was related to personality factors (negatively associated with conscientiousness and correlated with neuroticism), this didn't fully explain the link between sleep position and dream content. Of the 476 participants who reported having a dominant sleep position, only 5 per cent were habitual prone sleepers.

Yu thinks a prone sleeping position triggers particular kinds of dream content because of the way that the pressure on the body, including the genitals, and difficulty breathing, is converted into dream experiences. Sometimes this is done in a symbolic way, he argues, (hence the dreams about hand tools). Yu endorses a Freudian view of dreams, suggesting they protect sleep "by quenching the internal needs or eliminating the cues that alert the sleeping ego to the existence of the outer world."

In contrast to the associations between prone sleeping position and dream content, the frequency of sleeping in a supine (face up) or lateral position was almost entirely unrelated to the prevalence of different dream themes.

A major criticism of this research is the fact that participants were relied on to accurately recall their sleeping position and their dream content, a shortcoming that Yu acknowledged. The lack of any comparison between genders also seemed an unfortunate omission.

"This study provides the evidence that dream experiences, and in particular dream content, can be influenced by body posture during sleep," Yu concluded. His findings add to past research showing that right-sided sleepers had more positive dreams and fewer nightmares than left-sided sleepers.

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C K-C Yu (2012). The effect of sleep position on dream experiences. Dreaming DOI: 10.1037/a0029255

--Further reading-- Paraplegics walk in their dreams.

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Why teens should have their music and sports lessons in the evening

While you sleep your brain learns. Research with rats has shown how they rehearse maze-routes in their brains whilst they're dozing. And human research has demonstrated that learned material is better recalled after a sound sleep as opposed to a disturbed night. But what hasn't been looked at before now is the optimum time to leave between study and sleeping.

A team led by Johannes Holz has done just that, finding that "procedural learning" (practice at the kind of skill that you do, rather than talk about) is more effective right before sleep. Learning factual material, by contrast, (dependent on "declarative memory"), was found to be more effective when done in the afternoon, seven and a half hours before sleep, although the evidence for this was less convincing and should be treated with caution.

The researchers recruited 50 teenage girls (aged 16-17) to learn a series of word pairs and a finger-tapping task, either at 3pm in the afternoon or 9pm at night. The performance level of the afternoon and night groups was equivalent at the end of these initial learning tasks.

With the tapping task, it was the girls who learned right before sleep who showed the greatest gains in performance when they were re-tested after 24 hours and again 7 days later. Holz and his colleagues can't be sure why procedural learning is more effective just before sleep, but they think it probably has to do with the effect of sleep on protein synthesis and gene expression.

In contrast to the tapping task, performance on the word pairs after 24 hours was better in the afternoon-learning group. At the 7 day word-pairs test there was no difference in afternoon or evening learners. The fact that declarative learning was more effective in the afternoon suggests that this type of hippocampus-dependent memory has a different time course from procedural learning.

The findings, though preliminary, have obvious practical implications. "We propose that declarative memories, such as vocabulary words, should be studied in the afternoon and motor skills, like playing soccer or piano, should be trained in the late evening," the researchers said. "Most parents among us would have preferred the opposite results."

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Holz J, Piosczyk H, Landmann N, Feige B, Spiegelhalder K, Riemann D, Nissen C, and Voderholzer U (2012). The Timing of Learning before Night-Time Sleep Differentially Affects Declarative and Procedural Long-Term Memory Consolidation in Adolescents. PloS one, 7 (7) PMID: 22808287

-Further reading- Scientists find way to strengthen memories during sleep.

Post written by Christian Jarrett for the BPS Research Digest.

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Young male drivers are more vulnerable than older men to sleepiness

One might imagine the vigour of youth would allow young men to shrug off the effects of a lack of sleep. In fact, a new study on driving performance documents that young men are particularly vulnerable to the effects of sleepiness, far more than older men.

Ashleigh Filtness and his colleagues recruited 20 healthy young men (average age 23) and 20 healthy older men (average age 67) to complete two early afternoon driving challenges in a full-size simulator. One of the monotonous two-hour drives was completed after a normal night's sleep, as confirmed by a wrist actimeter that records nocturnal movement. The other two-hour drive was performed after a previous night's sleep of just five hours. The participants weren't allowed to consume alcohol for 36 hours before either test.

The researchers were mainly interested in lane drifts, in which all four wheels of the car left the lane the driver was supposed to be in. As you'd expect, these increased in the later stages of both the drives. Both groups of men also drifted more on the drive that followed less sleep. But the key finding was that the young men were affected far more drastically by a lack of sleep. For instance, in the last 30 minutes of the drive that followed a five-hour sleep, the young men averaged just over six lane drifts compared with fewer than two by the older men. This difference was also reflected in other measures - the younger men reported feeling more sleepy after a lack of sleep than the older men and this was confirmed by their brainwave recordings.

The new findings are consistent with previous night time studies in simulators and on the road that showed young male and female participants struggled more than older participants to maintain safe driving performance. They also help make sense of road accident data that show sleep-related incidents predominantly involve young male drivers.

However there are some complications in interpreting the new research. For example, it's likely the older drivers had more driving experience. Are they less vulnerable to sleepiness or simply better drivers? The researchers state only that both groups were experienced, with all participants having driven for over two years, more than three hours per week. Another complication acknowledged by the researchers is that young men typically sleep for longer than older men. This means the five-hour sleep limit condition was a greater departure from routine for the younger men.

A problem not mentioned in the paper is the potential influence of "stereotype threat" - whereby a fear of fulfilling stereotypes can undermine the performance of stereotyped groups. A researcher was present in the driving simulator room and it's possible the young men were aware of the negative attitudes commonly felt towards young male drivers and were affected as a result. A final weakness is the use of a simulator - the participants would have known any errors were inconsequential.

"The greater vulnerability of [young men] ... to sleep restriction potentially puts them at a greater driving risk under these circumstances, and may help further explain the relatively high proportion of young men being responsible for serious sleep related road collisions," the researchers said.
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Filtness, A., Reyner, L., and Horne, J. (2012). Driver sleepiness—Comparisons between young and older men during a monotonous afternoon simulated drive. Biological Psychology, 89 (3), 580-583 DOI: 10.1016/j.biopsycho.2012.01.002

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Inverse zombies studied using anaesthesia

Hospital medicine takes a pretty crude approach to consciousness. You're considered mentally AWOL if you don't respond to simple commands or physical prodding. But studies of post-operative patients have found that many of them recall having dreamt during anaesthesia. And in some disturbing cases they've even felt pain or heard the surgeons talking. This suggests that it's possible to be outwardly dead to the world, but conscious inside (locked-in patients and imaging studies of brain-injured patients in a persistent vegetative state also imply the same thing). Researchers have nicknamed people in this state "inverse zombies" - a play on the standard philosophical zombie concept, in which a person may appear to be outwardly conscious, but is in fact, dead inside.

A problem with much of the research into "inverse zombies" is that it's been conducted opportunistically in hospitals. The experimental set-up is messy, the patients have a variety of health complications, and they've often been given a cocktail of anaesthetic drugs. These studies have found rates of awareness during anaesthesia at around 0.023 to 1 per cent and rates of anaesthesia dreaming at rates of 6 to 53 per cent.

Now Valdas Noreika and his collaborators have performed a carefully controlled lab study of subjective (or "phenomenal") consciousness during anaesthesia, with the help of 40 healthy male university students. These brave souls were given progressively higher doses of one of four different anaesthetic drugs: dexmedetomidine; propofol (the drug that tragically killed Michael Jackson, who was using it as a sleeping aid); sevoflurane; and xenon. Dexmedetomidine and propofol are given intravenously; the other two are inhaled.

After the doping had begun, the researchers gave the participants the verbal command "Open your eyes!" at five minute intervals. Once a participant stopped responding they were considered to be unconscious in the traditional medical sense and the dose was gradually lowered until they responded again. Throughout, the researchers recorded the surface electrical activity from the front of the participants' brains using a "Bispectral Index Monitor (BIS)" - a form of electroencephalography (EEG), which provided an objective measure of the depth of sedation.

The induction phase - from the last response to "Open your eyes!" to the loss of responsiveness - lasted typically from around 5 to 10 minutes; the period of sedation or loss of responsiveness itself lasted around 10 minutes; this was followed by a 2 minute recovery phase and then 5 minutes of EEG scanning. At this point, the participants were interviewed about their subjective experiences during the time they were knocked out.

The key finding is that dreams or sensations were experienced during nearly 60 per cent of the anaesthesia sessions. These ranged from perceptual sensations (including "quick visual experiences"; out-of-body sensations; an altered sense of time); dream-like experiences (had a fragmentary dream about "a trip in Eastern Europe" said one participant); vision-based dreams related to the lab situation ("one of the nurses got suspended from her work"); and dreams with auditory content based on the lab situation ("a friend's roommate ... sitting next to me here in the lab, telling me we have to go to the city"). Sometimes these experiences were accompanied by negative emotions ("a bit anxious"); other times positive ("felt extraordinarily good"). The type of experiences didn't vary with the particular anaesthetic given.

Noreika and his team say these findings are important because they highlight the inadequacy of the standard medical definition of loss of consciousness (i.e. a loss of responsiveness), which is used in many anaesthesia-based studies into the neural correlates of consciousness. This standard definition, they argue, fails to take into account the frequent persistence of phenomenal consciousness in the absence of responsiveness. "Arguably, if one aims to explore the neural correlates of phenomenal consciousness, it would be fruitful to contrast the neural activity during dreaming anaesthesia vs. the neural activity during dreamless anaesthesia," they said.

The study is vulnerable to some obvious criticisms. The depth of sedation was shallower than is typically used in surgery, so the results may not generalise to higher doses of anaesthesia. Also, the participants were forewarned that they would be interviewed about any experiences they had whilst unconscious, which could have led them to come up with the kind of answers that they felt the researchers were after. Defending the validity of their results, Noreika's team pointed out that subjective reports of experience were more frequent when the objective BIS measure indicated shallower sedation - just as you'd expect if the experiences were real. "The results confirm that subjective experience may occur during clinically defined unresponsiveness," the researchers said.

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Noreika, V., Jylhänkangas, L., Móró, L., Valli, K., Kaskinoro, K., Aantaa, R., Scheinin, H., and Revonsuo, A. (2011). Consciousness lost and found: Subjective experiences in an unresponsive state. Brain and Cognition, 77 (3), 327-334 DOI: 10.1016/j.bandc.2011.09.002

Further reading: Check out this recent New Scientist feature article on consciousness and anaesthesia.


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Paraplegics walk in their dreams

In the land of dreams, the shackles of disability are cast asunder. That's the revelation from a new dream diary study featuring 15 paraplegics, 5 of whom were born with their condition. These volunteers (aged 22 to 84 years), recruited from a military hospital and a care home for people with motor disabilities, recorded their dreams for 6 weeks and French researchers compared the content with similar diaries kept by age-matched, able-bodied control participants.

All bar one of the disabled participants had at least one dream in which they moved their legs, including all five of the congenital paraplegics. As a group, the disabled participants experienced dreams about walking twice as often as they had dreams featuring their paraplegia. Moreover, voluntary leg movements featured in the dreams of the disabled more often than in the dreams of the able-bodied (38.2 per cent of dreams vs. 28.7 per cent). "I was not in a wheelchair but walking to a night club, to go dancing," recalled a 22-year-old person with congenital paraplegia in one typical dream report. There were some dreams featuring wheelchairs - these were experienced by eight of the disabled group and none of the controls.

Of the leg-movement mentions in the disabled participants' dream reports, the majority (46 per cent) pertained to walking. This is a lower percentage than found in the able-bodied diaries (64 per cent), but that's because the disabled dreamt more often about dancing and standing up. Activities like running, cycling, swimming and driving featured equally often in the dreams of both groups.

The disabled participants dreamed of walking even though they'd either never walked or hadn't walked for years. For example, two of the participants had been paralysed since sustaining gun-shot wounds during World War II and the France-Algeria war. There was no evidence that walking dreams became less frequent with duration of paralysis.

How do people with paraplegia dream of walking if it's something they've never experienced or haven't done for years? The researchers, led by Marie-Thérèse Saurat, believe it could reflect the activity of a "genetic, inherent walking programme", or the action of mirror neurons, which are stimulated during the day by the sight of other people performing movements. The latter explanation is especially favoured for dreams about cycling and other complex activities - it's "difficult to imagine that there is an innate programme for riding a bicycle, as this is a highly specialised activity recently developed in human history," the researchers said.

Why do paralysed people dream of walking? The researchers dismiss the psychoanalytic idea that the dreams are an expression of a subconscious wish. They argue that people with paraplegia are open about their desires to walk, and that their dreams are not dominated by walking to the extent you'd expect if they were compensating for lack of walking in waking life (in fact their dreams contained less walking than the control participants). Saurat and her colleagues suggest instead that walking in dreams may have an adaptive function: helping "consolidate the relevant neuronal mapping ... Notably, motor imagery training improves the movement performance of the intact muscles and increases basal ganglia activation in subjects with spinal cord injury."

These new findings add to previous research that found people born blind have visual experiences in their dreams and people born deaf can hear spoken language in theirs.
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Saurat, M., Agbakou, M., Attigui, P., Golmard, J., and Arnulf, I. (2011). Walking dreams in congenital and acquired paraplegia. Consciousness and Cognition, 20 (4), 1425-1432 DOI: 10.1016/j.concog.2011.05.015

Post written by Christian Jarrett for the BPS Research Digest.

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An afternoon nap tunes out negative emotions, tunes in positive ones

The perfect excuse for a siesta! People who stay awake throughout the day become progressively more sensitive to negative emotions. In contrast, those who take an afternoon nap are desensitised to negative emotions yet more responsive to positive ones. The new finding builds on past research by showing that not only does sleep deprivation cause emotional problems, a sleep boost can bring emotional advantages.

Ninad Gujar and his colleagues tested 36 participants (half were male; average age 21) on a face processing task, once at 12pm and then again at 5pm. Half the participants were given a 90-minute napping opportunity after the first task, whilst the others just went about their day as usual.

The task involved the participants looking at a computer screen that showed a male face pulling fearful, sad, angry and happy expressions at various intensities. The participants' goal quite simply was to rate each presentation of the face for intensity on a scale from 1 (definitely neutral) to 4 (mostly happy/sad etc).

For participants who stayed awake through the afternoon, their performance at 5pm, compared with at 12pm, demonstrated heightened sensitivity to fearful and angry facial expressions. By contrast, the participants who'd had a nap were less sensitive to fearful expressions at 5pm yet more sensitive to happy expressions. These emotional processing changes were also accompanied by mood differences: the no-nap group reported less positive mood later in the afternoon, compared with earlier, whereas the nap-group reported a decrease in negative mood.

The emotional processing changes observed among the nap-group were related to rapid-eye-movement (REM) sleep. EEG recordings taken while the nappers slept showed that those who obtained REM sleep were more likely to show the desensitisation to negative emotions and sensitisation to positive ones.

An alternative interpretation of the results is that napping affects visual processing, not emotional sensitivity. But the researchers don't think this stands up to much scrutiny, since any basic visual processing effects ought to have been uniform across the different emotions.

So, assuming the emotional sensitivity account is true, why might the non-napping participants have become more sensitive to negative emotions? One possibility, which is backed up by sleep deprivation research, is that the prefrontal cortex becomes fatigued through the day and therefore less able to dampen down emotional reactivity in the sub-cortex. Alternatively, perhaps heightened sensitivity to fear and anger is adaptive - as we fatigue through the day, it makes sense that we should become more vigilant towards these danger-based signals. Either way, a brief nap appears to give us an emotional recharge, altering the way we respond to other people's facial expressions. The implications for working practices are obvious.

'These data add to a growing collection of findings indicating a regulatory role for sleep in the optimal homeostasis of emotional brain function,' the researchers said, 'which if disrupted may have detrimental contributions to clinical symptomotology in affective disorders.'
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Gujar, N., McDonald, S., Nishida, M., and Walker, M. (2010). A Role for REM Sleep in Recalibrating the Sensitivity of the Human Brain to Specific Emotions. Cerebral Cortex, 21 (1), 115-123 DOI: 10.1093/cercor/bhq064

Earlier on the Digest: How to nap

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How to nap

Even naps as short as ten minutes have been shown to provide psychological benefits in terms of reduced fatigue and improved concentration (pdf). But would-be nappers face some strategic decisions, most obviously - does it matter whether I nap in my chair or ought I try to find somewhere to lie down? And then ... if remaining seated, is it okay to lean forwards and rest my head on a desk?

When it comes to napping while leaning back in a chair or car seat, past research has shown that the further you can lean back, the better, at least in terms of subjective fatigue and reaction times. Now Dayong Zhao and colleagues have addressed the leaning forward issue, comparing lying-down napping and leaning-forward napping, and they've found that the former is the most effective, but that the leaning-forward variety still has clear benefits compared with no nap at all.

Thirty undergrads, all regular nappers, had electrodes attached to their heads before lunch. Then they performed an 'oddball' auditory task in which they had to listen to a string of tones and listen out for the occasional one of a different pitch. Next they had lunch before splitting into three groups: one group enjoyed a twenty minute nap lying down; another enjoyed a twenty-minute nap leaning forwards onto a desk (plus pillow for comfort); the final group just spent the same time sitting quietly.

After this, all the participants performed a repeat of the oddball task whilst having their brainwaves recorded via electroencephalography. Zhao's team were particularly interested in the size and delay of the P300 - a brainwave measure of cognitive alertness.

Participants in both of the napping conditions showed benefits compared with their peers who'd been denied a nap. The nappers, leaning and lying, reported being in a better mood and feeling less sleepy and they performed better at the oddball task. When it came to the brainwave recordings, however, the leaning-forward nappers, unlike the lying-down nappers, showed no difference from the control group. Uniquely, the lying-down nappers showed an increased P300 amplitude, perhaps indicating increased cortical arousal on their part.

The message it seems is clear. A post-luncheon nap is beneficial to your mental functioning even if you're forced to rest your head on your desk. However, if you can find somewhere to lie down properly, then do, because the benefits of the nap will be that much greater.
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Zhao, D., Zhang, Q., Fu, M., Tang, Y., & Zhao, Y. (2010). Effects of physical positions on sleep architectures and post-nap functions among habitual nappers. Biological Psychology, 83 (3), 207-213 DOI: 10.1016/j.biopsycho.2009.12.008

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Scientists find way to strengthen memories during sleep

If only we could make more constructive use of all the time that we spend asleep. People have tried playing various tapes to themselves while they're dozing, from foreign vocab lists to stop-smoking mantras, but they're all the wrong side of useless. What we do know for sure is that sleep is important for memory consolidation, if only we could tap into this somehow. Now, finally, John Rudoy and colleagues have provided some elusive evidence for how learning during sleep can be enhanced.

Twelve participants looked on as fifty objects appeared one at a time in various locations on a computer screen. Importantly, as each object appeared it was accompanied by a characteristic noise - for example a cat appeared with a meow and a kettle with a whistle. Several rounds of learning took place until the participants had estimated the approximate location of each object at least once. A final pre-nap test was then performed so that the researchers knew how well participants knew each object location before they went to sleep.

That the participants had nodded off was confirmed with brain wave recordings via scalp electrodes. But here's the clever bit. As the participants dozed off into non-REM slow-wave sleep, the researchers played the sounds associated with 25 of the objects. The objects that were cued in this way were carefully chosen such that pre-nap memory performance had been equal for cued and un-cued objects.

The participants woke up after about an hour and the exciting finding is that although their overall memory accuracy was lower compared with before the nap, their performance for the objects cued whilst they slept was superior to un-cued objects, even though pre-nap performance for the two object groups had been equal.

The researchers also looked back at the brain wave signals recorded during sleep, comparing the brain's response to sounds associated with objects that were better remembered on waking relative to objects for which memory had deteriorated. They found the brain had responded more to sounds belonging to better remembered objects. "We propose that sound cues presented during sleep prompted preferential processing of corresponding object-location associations," the researchers said.

For sceptics who think the results may have nothing to do with sleep, the researchers repeated the noise cueing exercise with twelve participants who remained awake. In their case, sounds presented after learning made no difference to subsequent memory performance.
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Rudoy, J., Voss, J., Westerberg, C., & Paller, K. (2009). Strengthening Individual Memories by Reactivating Them During Sleep. Science, 326 (5956), 1079-1079 DOI: 10.1126/science.1179013

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