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.

_________________________________

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.

Post written by Christian Jarrett for the BPS Research Digest.

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."

_________________________________

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.

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.
_________________________________


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

Post written by Christian Jarrett for the BPS Research Digest.

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.

 _________________________________


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.


Post written by Christian Jarrett for the BPS Research Digest.