Sleep & Memory: Sleeping “Soundly”

A new study examined how sounds affect memory consolidation during sleep.

Participants were taught to associate 50 images with a random location on a computer screen. Each object was paired with a corresponding sound.

About 45 minutes later they took a nap of 90 minutes or less. This was long enough to enter deep, slow-wave sleep. But they didn’t nap long enough to enter rapid eye movement sleep – or REM sleep.

Twenty-five of the sounds were replayed as they slept. Participants were unaware of the sounds. Then they were tested again after waking from the nap.

Results suggest that the sounds improved their memory. Their performance was more accurate for the 25 objects that had been reinforced by sounds as they slept.

"The research strongly suggests that we don't shut down our minds during deep sleep," lead author John Rudoy said in a Northwestern University news release. "Rather this is an important time for consolidating memories."

Senior author Ken Paller told the New York Times that the method probably isn’t useful for teaching new information. But it may reinforce what you’ve already learned.

“One of our speculations is that SAT scores could be improved,” he said. He added that the technique might be able to help football players learn a playbook.

Recently the Sleep Education Blog reported that what you smell during sleep can affect your dreams. Learn more about sleep and memory.

Deep Sleep: Alzheimer’s, CPAP & OSA

A new study examined the effect of CPAP therapy on sleep in people with obstructive sleep apnea and Alzheimer’s disease.

The study involved 52 adults with OSA and Alzheimer’s disease; they had an average age of 78 years. The effect of CPAP therapy was compared with fake, placebo CPAP. Sleep was measured by overnight sleep study.

Results show that even one night of CPAP therapy had a positive effect on sleep. People in the CPAP group had a lower percentage of stage 1 sleep than the placebo group; they also had a higher percentage of stage 2 sleep.

The AASM reports that stage 1 sleep tends to occur when you first fall asleep and after awakenings during the night. This sleep is very light; a slight sound can wake you up.

It is not as easy to wake you up during stage 2 sleep. During this sleep stage your muscles are more relaxed.

Three weeks of CPAP therapy also provided sleep benefits. Participants spent less time awake during the night after first falling asleep. They had a lower percentage of stage 1 sleep and fewer arousals.

They also had a higher percentage of stage 3 sleep. This is known as “slow-wave sleep” or “deep sleep.”

The authors report that disrupted sleep is common in people with Alzheimer’s disease and OSA. CPAP therapy can help them reach and maintain deeper stages of sleep.

In August the same research team reported that CPAP therapy produced long-term benefits for people with Alzheimer’s disease and sleep apnea. There also is evidence that chronic sleep loss could play a role in the development of Alzheimer’s disease.

The AASM reports that OSA can occur in any age group; but it is more common between middle age and older age. The severity of untreated OSA also tends to progress over time.

On SleepEducation.com you can answer these questions to learn more about your risk for sleep apnea. Get help for sleep apnea at an AASM-accredited sleep center near you.

Sleep & Dyslexia: Reading Between the Lines

A new study from Italy analyzed the sleep of 16 children with developmental dyslexia. The results were published in the Oct. 1 issue of the journal Sleep.

The children had an average age of 11 years. Their sleep was evaluated during an overnight sleep study in a sleep lab. Results were compared with 11 children who read normally.

The study found that dyslexic children had a higher percentage of light, stage 2 sleep; they had a lower percentage of deep, slow wave sleep. These stages occur during non-rapid eye movement sleep – or NREM sleep. Children with dyslexia also had fewer periods of REM sleep.

Further analysis found additional differences during stage 2 sleep. Children with dyslexia had an increase in the power of fast, “sigma” brain waves; they also had an increased “sleep spindle” density. There were positive correlations between these measures and the children’s performance on reading tests.

A sleep spindle is a brief burst of rhythmic brain activity; it is a unique aspect of stage 2 sleep. “Density” refers to the number of sleep spindles that occur per minute of stage 2 sleep.

Dyslexic children had an average of 6.2 sleep spindles per minute; normal readers had only 3.5 sleep spindles per minute.

The NINDS reports that dyslexia is a brain-based type of learning disability; it involves a reading impairment that occurs in a person who has normal intelligence.

The authors suggest that increases in sleep spindles and sigma power may be markers of dyslexia; these markers may be related to the severity of reading impairment. The results also support the hypothesis that sleep plays an important role in learning and memory.

The authors note that only one other study has measured brain activity during sleep in children with reading disabilities; the results were published in the journal Sleep in 1993. That study found similar changes in the sleep of reading-disabled boys.

Learn more about sleep stages on SleepEducation.com.

Image by Shanubi

Sleep & Long-Term Memory: A “Sharp” Discovery

Researchers report that they have discovered how sleep plays a role in memory consolidation.

The process involves “sharp wave ripples.” These are short, intense, compressed oscillations in the brain; they occur during the sleep stage of slow-wave sleep.

The research team suggests that these events are responsible for consolidating memory. The sharp wave ripples transfer learned information to the brain region where long-term memories are stored.

“This specific brain pattern is the cause behind long-term memory formation,” study co-author György Buzsáki said in a Rutgers news release.

Buzsáki explained that the sharp wave ripples “teach” the brain to form a long-term memory. The ripples occur hundreds to thousands of times during sleep; this helps explain how a momentary event can be ingrained in the memory for a lifetime.

The finding may aid the development of effective treatments for memory disorders.

Learn more about sleep and memory.

Alcohol & Sleep: Nix the Nightcaps

A new survey by the Department of Health in England shows that many people fail to realize that alcohol can have a negative effect on sleep; 58 percent of surveyed drinkers were unaware that drinking can cause sleep problems.

One problem is that drinking alcohol may force you to go the bathroom more often during the night. The Department of Health reports that alcohol stops the brain from releasing vasopressin; this chemical helps regulate the amount of water in your body.

Dehydration also can occur during the night as your body gets rid of too much water; this can cause sleep-disrupting headaches.

According to a 2005 review by the AASM, decades of studies also show that alcohol disrupts your natural sleep cycle. These disruptions tend to be dose dependent; they increase as the amount of alcohol you drink increases.

The review reports that alcohol initially may help you fall asleep. Then for a few hours there may be a short-term increase in deep, slow-wave sleep. But there also may be a decrease in rapid eye movement sleep – or REM sleep.

A 2002 study in the journal Sleep showed that these alcohol-induced changes in REM sleep can cause memory loss. The Department of Health suggests that this may help explain the “foggy” memory that many people have after a night of heavy drinking.

The AASM review also found that a withdrawal effect can occur later in the night. Your sleep may become lighter and more fragmented; the number and duration of awakenings may increase. Overall, it is likely that your sleep will be unrefreshing after drinking alcohol.

The review also reports that alcohol use can worsen obstructive sleep apnea. Breathing pauses may occur more often and last longer.

Research clearly shows that alcohol can be disruptive to your sleep. Despite this evidence, many people continue to have a “nightcap” before going to bed.

A 2005 study in the journal Sleep found that about 11 percent of normal sleepers reported using alcohol to sleep. Results also show that the use of alcohol for sleep was an independent predictor of insomnia; about 29 percent of people with insomnia reported that in the past year they had used alcohol to help them fall sleep.

So what’s the bottom line? Nix the nightcap: Avoid drinking any alcohol before bedtime.

Effective treatments are available if you are struggling with insomnia. Contact an AASM-accredited sleep center for help.

Image by Craig Baker

Teen Depression: Sleep Cycle is a Risk Marker

A recent study shows that a teen’s sleep pattern may be a marker of his or her risk for developing depression.

The study involved 48 teens who were “at risk” for depression; they had a high risk because of a parental history of depression. The at-risk teens were compared with 48 other teens in a control group; these teens had no personal or family history of a mental health problem.

The research team monitored the sleep cycles of the teens for three days. They also used lab tests to measure levels of the hormone cortisol; increased cortisol levels are related to depression in adults. The teens were monitored for up to five years.

Results show that the at-risk teens took less time to enter the stage of rapid eye movement sleep – or REM sleep. They also had more REM sleep and elevated cortisol levels. These teens were more likely to develop depression by the end of the five-year study period.

Previous studies had shown that depressed adults enter REM sleep earlier in the sleep cycle; but it was unclear if this pattern also occurred in teens.

“This study is an initial step in determining baseline measures that differentiate healthy adolescents from those who are likely to develop depression,” lead author Dr. Uma Rao said in a UT Southwestern Medical Center statement.

Rao cautioned that REM sleep and cortisol levels are not diagnostic tools; but they are “vulnerability markers” for depression.

“If we can identify factors such as sleep and cortisol and their role, we could start the prevention process,” she said.

The NIMH reports that depression often occurs along with another disorder in teens; examples include anxiety, eating disorders and substance abuse. By age 15, girls are twice as likely as boys to have had a major depressive episode.

Earlier this year the Sleep Education Blog reported that sleep problems in children may predict the future onset of depression. A study showed that sleep problems at age 8 predict depression at age 10; but depression at age 8 did not predict sleep problems at age 10. The study found a strong genetic link for the presence of sleep problems.

Sleep & Memory: “Replay” to Remember

A study published yesterday reports that the role of sleep in memory consolidation has been confirmed.

The study involved mice that ran a maze and then slept. Electrodes monitored their brain activity. While awake the brains of the mice “mapped” the pattern of the maze. Results show that their brains “replayed” this pattern during slow-wave sleep.

"Ours is the first study to demonstrate this link between memory replay and memory consolidation,” study co-author Susumu Tonegawa said in an MIT statement. “The sleeping brain must replay experiences like video clips before they are transformed from short-term into long-term memories."

The study identified a specific circuit in the brain that is involved in this process - the “trisynaptic pathway.” It is located in the “hippocampus.” This is a complex brain structure that is shaped like a seahorse.

In some of the mice the trisynaptic pathway was blocked. This impaired the replay process during sleep. Only mice with a functioning trisynaptic pathway were able to form long-term memories of the maze.

"We demonstrated that this pathway is crucial for the transformation of a recent memory, formed within a day, to a remote memory that still exists at least six weeks later," Tonegawa said.

Read more about sleep and memory on the Sleep Education Blog. Learn more about the stages of sleep on SleepEducation.com.

REM Sleep Enhances Creativity

A new study reports that rapid eye movement sleep – or “REM sleep” – enhances creative problem solving.

Participants completed a creativity task in the morning. Afterward, some took a nap that included REM sleep; some took a nap without REM sleep; and some simply rested quietly. Then they were tested on the creativity task in the afternoon.

Results show that REM sleep enhanced the integration of unassociated information for creative problem solving. Members of the REM sleep group improved their performance on the creativity task by almost 40 percent. There was no performance improvement for members of the other two groups.

“We found that – for creative problems that you’ve already been working on – the passage of time is enough to find solutions,” study author Sara Mednick, PhD, said in a UCSD statement. “However, for new problems, only REM sleep enhances creativity.”

The AASM reports that there are multiple stages of sleep in a sleep cycle. Each complete cycle lasts about 90 to 110 minutes. REM sleep tends to be the final stage of the sleep cycle in normal adult sleep.

Learn more about REM sleep and sleep stages on SleepEducation.com.

Diabetes, Sleep Apnea & REM Sleep

A new study in the Journal of Clinical Sleep Medicine links obstructive sleep apnea to type 2 diabetes. It shows that there is an increased risk of diabetes in people who have sleep apnea during rapid eye movement sleep – or “REM sleep.”

The multi-ethnic study involved 1,008 people who were evaluated for sleep apnea; 67 percent were African American, 17 percent were Caucasian and 15 percent were Hispanic. Sleep apnea was diagnosed in 74 percent of participants.

Results show that people with sleep apnea during REM sleep were twice as likely to have type 2 diabetes. The risk of diabetes in middle-aged adults with sleep apnea was increased by almost three times. Overall, 30 percent of the participants with sleep apnea had diabetes.

“Generally, OSA is worse in REM sleep compared to non-REM sleep,” study author Dr. Kamran Mahmood told the AASM. “This may be the reason for closer association of REM-related OSA and type 2 diabetes.”

The study also reports that sleep fragmentation caused by sleep apnea may reduce REM sleep time.

Learn more about sleep apnea and diabetes. Read more about REM sleep and sleep stages on SleepEducation.com.

Get help for sleep apnea at an AASM-accredited sleep center near you.

How Sleep Disorders May Affect Your Dreams

Sleep disorders can reduce both the quantity and quality of your sleep. Can they also affect your dreams?

A new review examined the current research. Only a small number of studies have focused on this subject. But results suggest that a couple of common sleep disorders may have an impact on your dreams.

People with insomnia are more likely to recall their dreams. The content of their dreams tends to reflect current stressors.

Breathing-related dreams are rare in people with sleep apnea.

People with narcolepsy tend to have bizarre dreams with a negative tone. This may be related to their disrupted sleep cycles.

The complex process of sleep involves multiple stages that make up a sleep cycle. Each complete cycle lasts about 90 to 110 minutes. Most adults will go through four to six cycles in a full night of sleep.

Most dreams occur during rapid eye movement (REM) sleep. This tends to be the final stage of the sleep cycle in normal adult sleep.

But people who have narcolepsy tend to go quickly into REM sleep. These events are called sleep-onset REM periods (SOREMPs).

Overall, the studies in the review support the “continuity hypothesis” of dreaming. This states that dreams reflect the issues and concerns of your life.

Image by Magdalena Swebodzinska

Research Catching Up to Jet Lag

Results from a new study in Current Biology may lead to more effective treatments for jet lag and shift work sleep disorder.

Both sleep disorders involve a disruption to your body’s circadian timing system. This system regulates the timing of when you sleep and wake.

The study shows that this disruption occurs in two separate groups of neurons in the brain. It also involves two different sleep stages.

Both groups of neurons are located in the “suprachiasmatic nucleus.” This part of the brain acts as a body clock. It regulates daily functions such as body temperature, hormone levels and sleepiness.

The study found that one set of neurons is closely linked with slow wave sleep. This is also called “deep sleep.” These neurons receive light information directly from the eyes. With these light and dark signals, your pattern of deep sleep can adjust to a new schedule in a couple of days.

Another set of neurons controls rapid eye movement – or REM – sleep. Most of your dreams occur during this stage. These neurons do not receive direct light information. As a result your pattern of REM sleep can be out of sync for a week or more when you cross time zones.

The researchers exposed lab rats to an artificial light-dark schedule. This simulated a trip from Paris to New York.

They also found that the time change disrupted the normal progression of sleep stages. There was an overlap of slow wave sleep and REM sleep right after the simulated jet lag. The rats also were more likely to enter REM sleep earlier than they should.

The study helps explain why it takes the body so long to adapt to a new time zone. After a long flight it typically takes about one day per time zone for your body clock to adjust to the local time.

Researcher Horacio de la Iglesia expects that the study will have a positive impact on treatments for jet lag and shift work.

"We can go back to the treatments that are believed to be effective and see where they might be acting in the circuitry of these neuron centers, then refine them to be more effective," he said in a University of Washington statement.

Image by Kossy