Sleep enhances emotional memory, preserves emotional intensity

Sleeping on a negative thought helps preserve it, a recent study concluded. Participants were shown images. Some of the images were positive, others negative. Twelve hours later, those who’d been asleep had better recognition of the images. The negative images and the positive ones.

Emotional reaction to the negative images was greatly diminished over time when participants stayed awake. But for people who slept, the reaction to the negative images was just as strong as when they’d first viewed them. Researchers also linked a longer time spent in REM sleep with preserving emotional reactions to the images. The study was unable to connect REM sleep with recognizing the images.

The study was conducted by the Department of Psychology and Neuroscience and Behavior Program at the University of Massachusetts. It appeared in the January issue of The Journal of Neuroscience.

REM Sleep Boosts Creative Problem Solving

The sleep stage sometimes characterized by vivid dreams is when your mind goes to work for you. A study presented at the Annual Convention of the American Psychological Association demonstrated how REM sleep can boost memory and creative problem solving.

Sleep researchers at the University of California, San Diego, used a word association test to show the difference REM sleep makes on memory. Participants took the test in the morning and the afternoon, after either a nap with REM sleep, a short nap without REM sleep or a quiet rest period.

The first part of the test resembled SAT word-analogy questions. One sample question was:

Q: Chips:salty::candy:______
A: Sweet

After a 90 minute rest period, the subjects moved onto the second round. That involved using the first round’s answers as a response to three seemingly unrelated words.

Q: cookie: heart: sixteen
A:Sweet

The participants who were allowed REM sleep performed better in the afternoon, while the people who didn’t nap or get any REM sleep saw no improvement.

The authors believe REM sleep helped connect networks of previously unassociated information in the brain, which helped creative problem solving.

The findings are similar another recent study involving dreams and memory. Both results suggest REM sleep is when we pull together all the information from the day and turn it into memory.

Why Do We Dream?

A new paper suggests that the purpose of dreams may be more than just psychological.

Author Dr. J. Allan Hobson proposes a “theory of protoconsciousness.” He is a professor of psychiatry at Harvard Medical School.

Hobson writes that REM sleep provides “a virtual reality model of the world.” Most dreams occur during this sleep stage.

He thinks that dreams have a functional use. They allow the brain to get tuned up for wakefulness.

“It helps explain a lot of things, like why people forget so many dreams,” Hobson told the New York Times. “Dreams are tuning the mind for conscious awareness.”

This dream theory fits within his broader concept of the purpose of sleep. He summarized his perspective in the title of a 2005 paper: “Sleep is of the brain, by the brain and for the brain.”

Recently Hobson was the co-author of a study in the journal Sleep that investigated lucid dreaming. Results suggest that lucid dreaming is a “unique, hybrid state of sleep;” it involves features of both REM sleep and wakefulness.

In 2008 Hobson and colleagues explored similarities between the normal mental state of dreaming and the abnormal mental state of psychosis. They reported that normal dreaming and schizophrenic thinking share a common degree of “cognitive bizarreness.”

Other dream theories abound: Dreams depict your emotions. They reflect the issues and concerns of your life. They act as a defense mechanism by simulating waking threats.

Read more about interpreting dreams and why we sleep on the Sleep Education Blog. Learn more about dreams and nightmares on SleepEducation.com.

Image by Cornelia Kopp

Lucid Dreaming: A Sleep-Wake Hybrid

A new study in the Sept. 1 issue of the journal Sleep investigated lucid dreaming.

What is lucid dreaming? It involves the conscious awareness of dreaming while you are still asleep.

Lucid dreaming combines aspects of waking and dreaming. You have hallucinatory dream activity along with reflective awareness; you realize that you are not awake and are dreaming. In contrast, during non-lucid dreams you mistakenly think that you are awake. Lucid dreaming also can involve the ability to control what happens during the dream.

Lucid dreams tend to occur after several hours of sleep; they are more common during later periods of rapid eye movement sleep – or REM sleep. The longest period of REM sleep may last for an hour near the end of the night. REM sleep makes up about 25 percent of total sleep time in normal adult sleep.

According to the authors, spontaneous lucidity is rare. But people can be trained to become lucid. A special electronic device can help induce lucidity; these devices emit specific light or sound signals.

But most often the training is done through pre-sleep “autosuggestion.” Before going to sleep, you tell yourself to recognize when you are dreaming; you prepare yourself to notice the bizarre events of the dream.

The authors also report that it is possible for you to communicate that you have become lucid during sleep; you can make a sequence of voluntary eye movements as a signal.

The study preparation involved 20 college students in Bonn, Germany. They took part in weekly lucidity training sessions. After four months, six people claimed to be lucid more than three times per week.

These six volunteers participated in the study. Their sleep was monitored during multiple overnight sleep studies.

Results show that three of the six volunteers were able to have a lucid dream in the sleep lab. In each case, lucidity occurred in the morning hours.

The dreamers were able to signal that they had become lucid with a pattern of horizontal eye movements. Lucidity also was confirmed by self-report after waking.

Brain-wave recordings confirmed that lucid dreaming occurs during sleep. But the recordings also showed that it differs from REM sleep.

The authors suggest that lucid dreaming is a “unique, hybrid state of sleep;” it involves features of both REM sleep and wakefulness. They conclude that lucidity requires a shift in brain activity during sleep.

Image by Cornelia Kopp

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.