Contradictory findings on how the full moon affect our sleep

A Swiss research study conducted last year showed that the full moon affects sleep. The findings demonstrated that people average 20 minutes less sleep, take five minutes longer to fall asleep and experience 30 minutes more of REM sleep, during which most dreaming is believed to occur.

Different outcome

Numerous studies through the years have attempted to prove or disprove the hypothesis that lunar phases affect human sleep. But results have been hard to repeat. A group of researchers at the famed Max Planck Institute and elsewhere analyzed data from more than 1,000 people and 26,000 nights of sleep, only to find no correlation.

International researchers are being urged to publish their results in hopes of getting to the bottom of the question. Michael Smith and his co-researchers at Sahlgrenska Academy have analyzed data generated by a previous sleep study and compared them with the lunar cycle.

20 minutes less sleep

Based on a study of 47 healthy 18-30 year-olds and published in Current Biology, the results support the theory that a correlation exists.

“Our study generated findings similar to the Swiss project,” Michael Smith says. “Subjects slept an average of 20 minutes less and had more trouble falling asleep during the full moon phase. However, the greatest impact on REM sleep appeared to be during the new moon.”

More susceptible brain

The retrospective study by the Gothenburg researchers suggests that the brain is more susceptible to external disturbances when the moon is full.

“The purpose of our original study was to examine the way that noise disturbs sleep,” Mr. Smith continues. “Re-analysis of our data showed that sensitivity, measured as reactivity of the cerebral cortex, is greatest during the full moon.”

Greater cortical reactivity was found in both women and men, whereas only men had more trouble falling asleep and slept less when the moon was full. Skeptics warn that both age and gender differences may be a source of error, not to mention more subtle factors such as physical condition and exposure to light during the day.

Need for more studies

Though fully aware of the issues, Mr. Smith is not prepared to dismiss the results of the Gothenburg study.

“The rooms in our sleep laboratories do not have any windows,” he says. “So the effect we found cannot be attributable to increased nocturnal light during full moon. Thus, there may be a built-in biological clock that is affected by the moon, similar to the one that regulates the circadian rhythm. But all this is mere speculation – additionally, more highly controlled studies that target these mechanisms are needed before more definitive conclusions can be drawn.”

The article Human sleep and cortical reactivity are influenced by lunar phase is published in Current Biology.

Learn Dutch in your sleep

When you have learned words in another language, it may be worth listening to them again in your sleep. A study funded by the Swiss National Science Foundation (SNSF) has now shown that this method reinforces memory.

​Reluctant students and sleepyheads take note: a study conducted at the universities of Zurich and Fribourg has shown that German-speaking students are better at remembering the meaning of newly learned Dutch words when they hear the words again in their sleep. “Our method is easy to use in daily life and can be adopted by anyone,” says study director and biopsychologist Björn Rasch. However, the results were obtained in strictly controlled laboratory conditions. It remains to be seen whether they can be successfully transferred to everyday situations.

Quiet playback

In their trial, which has been published in the journal “Cerebral Cortex”, Thomas Schreiner and Björn Rasch asked 60 volunteers to learn pairs of Dutch and German words at ten o’clock in the evening. Half of the volunteers then went to bed. While they slept, some of the Dutch words they had learned before going to bed were played back quietly enough not to awaken them. The remaining volunteers stayed awake to listen to the Dutch words on the playback.

The scientists awoke the sleeping volunteers at two in the morning, then tested everyone’s knowledge of the new words a little later. The group that had been asleep were better at remembering the German translations of the Dutch words they had heard in their sleep. The volunteers who had remained awake were unable to remember words they had heard on the playback any better than those they had not.

Reinforcement of spontaneous activation

Schreiner and Rasch believe that their results provide further evidence that sleep helps memory, probably because the sleeping brain spontaneously activates previously learned subject matter. Playing this subject matter back during sleep can reinforce this activation process and thus improve recall. For example, a person who plays a memory card game to the scent of roses, and is then re-exposed to the same scent while asleep, is subsequently better at remembering where a particular card is in the stack, as Rasch was able to show in another study a few years ago.

Schreiner and Rasch have now observed the beneficial effect of sleep on learning foreign words. A certain amount of swotting is still needed, though. “You can only successfully activate words that you have learned before you go to sleep. Playing back words you don’t know while you’re asleep has no effect,” says Schreiner.

Little or poor sleep may be associated with worse brain function when aging

Research published today in PLOS ONE by researchers at the University of Warwick indicates that sleep problems are associated with worse memory and executive function in older people.

Analysis of sleep and cognitive (brain function) data from 3,968 men and 4,821 women who took part in the English Longitudinal Study of Ageing (ELSA), was conducted in a study funded by the Economic and Social Research Council (ESRC). Respondents reported on the quality and quantity of sleep over the period of a month.

The study showed that there is an association between both quality and duration of sleep and brain function which changes with age.

In adults aged between 50 and 64 years of age, short sleep (<6hrs per night) and long sleep (>8hrs per night) were associated with lower brain function scores. By contrast, in older adults (65-89 years) lower brain function scores were only observed in long sleepers.

Dr Michelle A Miller says “6-8 hours of sleep per night is particularly important for optimum brain function, in younger adults”. These results are consistent with our previous research, which showed that 6-8 hours of sleep per night was optimal for physical health, including lowest risk of developing obesity, hypertension, diabetes, heart disease and stroke”.

Interestingly, in the younger pre-retirement aged adults, sleep quality did not have any significant association with brain function scores, whereas in the older adults (>65 years), there was a significant relationship between sleep quality and the observed scores.

“Sleep is important for good health and mental wellbeing” says Professor Francesco Cappuccio, “Optimising sleep at an older age may help to delay the decline in brain function seen with age, or indeed may slow or prevent the rapid decline that leads to dementia”.

Dr Miller concludes that “if poor sleep is causative of future cognitive decline, non-pharmacological improvements in sleep may provide an alternative low-cost and more accessible Public Health intervention, to delay or slow the rate of cognitive decline”.

Does the moon affect our sleep?

Popular beliefs about the influence of the moon on humans widely exist. Many people report sleeplessness around the time of full moon. In contrast to earlier studies, scientists from the Max Planck Institute of Psychiatry in Munich did not observe any correlation between human sleep and the lunar phases. The researchers analyzed preexisting data of a large cohort of volunteers and their sleep nights. Further identification of mostly unpublished null findings suggests that the conflicting results of previous studies might be due to a publication bias.

For centuries, people have believed that the moon cycle influences human health, behavior and physiology. Folklore mainly links the full moon with sleeplessness. But what about the scientific background?

Several studies searched in re-analyses of pre-existing datasets on human sleep for a lunar effect, although the results were quite varying and the effects on sleep have rarely been assessed with objective measures, such as a sleep EEG. In some studies women appeared more affected by the moon phase, in others men. Two analyses of datasets from 2013 and 2014, each including between 30 and 50 volunteers, agreed on shorter total sleep duration in the nights around full moon. However, both studies came to conflicting results in other variables. For example, in one analysis the beginning of the REM-sleep phase in which we mainly dream was delayed around new moon, whereas the other study observed the longest delay around full moon.

To overcome the problem of possible chance findings in small study samples, scientists now analyzed the sleep data of overall 1,265 volunteers during 2,097 nights. “Investigating this large cohort of test persons and sleep nights, we were unable to replicate previous findings,” states Martin Dresler, neuroscientist at the Max Planck Institute of Psychiatry in Munich, Germany, and the Donders Institute for Brain, Cognition and Behaviour in Nijmegen, Netherlands. “We could not observe a statistical relevant correlation between human sleep and the lunar phases.” Further, his team identified several unpublished null findings including cumulative analyses of more than 20,000 sleep nights, which suggest that the conflicting results might be an example of a publication bias (i.e. the file drawer problem).

The file drawer problem describes the phenomenon, that many studies may be conducted but never reported – they remain in the file drawer. One much-discussed publication bias in science, medicine and pharmacy is the tendency to report experimental results that are positive or show a significant finding and to omit results that are negative or inconclusive.

Up to now, the influence of the lunar cycle on human sleep was investigated in re-analyses of earlier studies which originally followed different purposes. “To overcome the obvious limitations of retrospective data analysis, carefully controlled studies specifically designed for the test of lunar cycle effects on sleep in large samples are required for a definite answer,” comments Dresler.

Sleep After Learning Strengthens Connections Between Brain Cells and Enhances Memory

In study published today in Science, researchers at NYU Langone Medical Center show for the first time that sleep after learning encourages the growth of dendritic spines, the tiny protrusions from brain cells that connect to other brain cells and facilitate the passage of information across synapses, the junctions at which brain cells meet. Moreover, the activity of brain cells during deep sleep, or slow-wave sleep, after learning is critical for such growth.

The findings, in mice, provide important physical evidence in support of the hypothesis that sleep helps consolidate and strengthen new memories, and show for the first time how learning and sleep cause physical changes in the motor cortex, a brain region responsible for voluntary movements. 

“We’ve known for a long time that sleep plays an important role in learning and memory. If you don’t sleep well you won’t learn well,” says senior investigator Wen-Biao Gan, PhD, professor of neuroscience and physiology and a member of the Skirball Institute of Biomolecular Medicine at NYU Langone Medical Center. “But what’s the underlying physical mechanism responsible for this phenomenon? Here we’ve shown how sleep helps neurons form very specific connections on dendritic branches that may facilitate long-term memory. We also show how different types of learning form synapses on different branches of the same neurons, suggesting that learning causes very specific structural changes in the brain.”

On the cellular level, sleep is anything but restful: Brain cells that spark as we digest new information during waking hours replay during deep sleep, also known as slow-wave sleep, when brain waves slow down and rapid-eye movement, as well as dreaming, stops. Scientists have long believed that this nocturnal replay helps us form and recall new memories, yet the structural changes underpinning this process have remained poorly understood.

To shed light on this process, Dr. Gan and colleagues employed mice genetically engineered to express a fluorescent protein in neurons. Using a special laser-scanning microscope that illuminates the glowing fluorescent proteins in the motor cortex, the scientists were then able to track and image the growth of dendritic spines along individual branches of dendrites before and after mice learned to  balance on a spin rod. Over time mice learned how to balance on the rod as it gradually spun faster. “It’s like learning to ride a bike,” says Dr. Gan. “Once you learn it, you never forget.”

After documenting that mice, in fact, sprout new spines along dendritic branches, within six hours after training on the spinning rod, the researchers set out to understand how sleep would impact this physical growth. They trained two sets of mice: one trained on the spinning rod for an hour and then slept for 7 hours; the second trained for the same period of time on the rod but stayed awake for 7 hours. The scientists found that the sleep-deprived mice experienced significantly less dendritic spine growth than the well-rested mice. Furthermore, they found that the type of task learned determined which dendritic branches spines would grow.

Running forward on the spinning rod, for instance, produced spine growth on different dendritic branches than running backward on the rod, suggesting that learning specific tasks causes specific structural changes in the brain.

“Now we know that when we learn something new, a neuron will grow new connections on a specific branch,” says Dr. Gan. “Imagine a tree that grows leaves (spines) on one branch but not another branch. When we learn something new, it’s like we’re sprouting leaves on a specific branch.”

Finally, the scientists showed that brain cells in the motor cortex that activate when mice learn a task reactivate during slow-wave deep sleep. Disrupting this process, they found, prevents dendritic spine growth. Their findings offer an  important insight into the functional role of neuronal replay—the process by which the sleeping brain rehearses tasks learned during the day—observed in the motor cortex.

“Our data suggest that neuronal reactivation during sleep is quite important for growing specific connections within the motor cortex,” Dr. Gan adds.

(Image: Shutterstock)

Losing the left side of the world: Rightward shift in human spatial attention with sleep onset

Unilateral brain damage can lead to a striking deficit in awareness of stimuli on one side of space called Spatial Neglect. Patient studies show that neglect of the left is markedly more persistent than of the right and that its severity increases under states of low alertness. There have been suggestions that this alertness-spatial awareness link may be detectable in the general population. Here, healthy human volunteers performed an auditory spatial localisation task whilst transitioning in and out of sleep. We show, using independent electroencephalographic measures, that normal drowsiness is linked with a remarkable unidirectional tendency to mislocate left-sided stimuli to the right. The effect may form a useful healthy model of neglect and help in understanding why leftward inattention is disproportionately persistent after brain injury. The results also cast light on marked changes in conscious experience before full sleep onset.

Full Article

(Image: ALAMY)

Genes discovered linking circadian clock with eating schedule

For most people, the urge to eat a meal or snack comes at a few, predictable times during the waking part of the day. But for those with a rare syndrome, hunger comes at unwanted hours, interrupts sleep and causes overeating.

Now, Salk scientists have discovered a pair of genes that normally keeps eating schedules in sync with daily sleep rhythms, and, when mutated, may play a role in so-called night eating syndrome. In mice with mutations in one of the genes, eating patterns are shifted, leading to unusual mealtimes and weight gain. The results were published in Cell Reports today.

"We really never expected that we would be able to decouple the sleep-wake cycle and the eating cycle, especially with a simple mutation," says senior study author Satchidananda Panda, an associate professor in Salk’s Regulatory Biology Laboratory. "It opens up a whole lot of future questions about how these cycles are regulated."

More than a decade ago, researchers discovered that individuals with an inherited sleep disorder often carry a particular mutation in a protein called PER2. The mutation is in an area of the protein that can be phosphorylated—the ability to bond with a phosphate chemical that changes the protein’s function. Humans have three PER, or period, genes, all thought to play a role in the daily circadian clock and all containing the same phosphorylation spot.

The Salk scientists joined forces with a Chinese team led by Ying Xu of Nanjing University to test whether mutations in the equivalent area of PER1 would have the same effect as those in PER2 that caused the sleep disorder. So they bred mice to lack the mouse period genes, and added in a human PER1 or PER2 with a mutation in the phosphorylation site. As expected, mice with a mutated PER2 had sleep defects, dozing off earlier than usual. The same wasn’t true for PER1 mutations though.

"In the mice without PER1, there was no obvious defect in their sleep-wake cycles," says Panda. "Instead, when we looked at their metabolism, we suddenly saw drastic changes."

Mice with the PER1 phosphorylation defects ate earlier than other mice—causing them to wake up and snack before their sleep cycle was over—and ate more food throughout their normal waking period. When the researchers looked at the molecular details of the PER1 protein, they found that the mutated PER1 led to lower protein levels during the sleeping period, higher levels during the waking period, and a faster degradation of protein whenever it was produced by cells.

Panda and his colleagues hypothesize that normally, PER1 and PER2 are kept synchronized since they have identical phosphorylation sites—they are turned on and off at the same times, keeping sleep and eating cycles aligned. But a mutation in one of the genes could break this link, and cause off-cycle eating or sleeping.

"For a long time, people discounted night eating syndrome as not real," says Panda. "These results in mice suggest that it could actually be a genetic basis for the syndrome." The researchers haven’t yet tested, however, whether any humans with night eating syndrome have mutations in PER1.

When Panda and Xu’s team restricted access to food, providing it only at the mice’s normal meal times, they found that even with a genetic mutation in PER1, mice could maintain a normal weight. Over a 10-week follow-up, these mice—with a PER1 mutation but timed access to food—showed no differences to control animals. This tells the researchers that the weight gain caused by PER1 is entirely caused by meal mistiming, not other metabolic defects.

Next, they hope to study exactly how PER1 controls appetite and eating behavior—whether its molecular actions work through the liver, fat cells, brain or other organs.