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Dreams & Emotions

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REM sleep, in which dreams occur, also may help take the edge off painful memories.


Transcript

Dreaming away the pain. I’m Bob Hirshon and this is Science Update.

Bad experiences often feel less painful after a good night’s sleep. That’s no coincidence, according to neuroscientist Matthew Walker of the University of California, Berkeley. He and his colleagues showed emotionally charged images to volunteers at two different times. Those who slept in between the viewings had milder emotional responses the second time around. The crucial factor was a kind of sleep called REM sleep, which is linked to dreaming.

Walker:
The quality of that sleep accurately predicted how much of a dissipation in the emotional reaction you would have the next morning.

Looking closer, he found evidence that REM sleep helps the brain re-process emotional memories, without the stress-related brain chemicals that accompany them while we’re awake. The findings could lead to better treatments for post-traumatic stress disorder, which is also linked to poor REM sleep. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

It's long been known that our brains actually do a lot of work while we sleep. The brain is especially active during a phase of sleep called REM (Rapid Eye Movement), which has been linked to learning and memory. For example, studies have found that people perform better on tests after a night of sleep than after the same amount of waking hours, and that REM sleep seems to be crucial to this process. (That's one reason why pulling an all-nighter before an exam isn't such a great idea.) 

This study looked at sleep's effect on the relationship between memory and emotion. It's safe to say that for most people, emotionally troubling experiences feel less disturbing over time, and often seem better the day after they happen. People with post-traumatic stress disorder (PTSD), on the other hand, relive painful memories as if they just happened, over a period of weeks, months, or even years. PTSD usually sets in after an especially frightening tragic event, and soldiers returning home from war are particularly vulnerable to it.

So, the question is, what makes memories of bad experiences less painful for most people, and how might that malfunction in PTSD? According to this experiment, REM sleep seems to play a key role. The researchers showed volunteers sad or upsetting images, sent them away for 12 hours, and then brought them back to show them the same images again. Although the gap between sessions was always 12 hours, one group saw the images first in the morning and later in the evening, with no sleep in between. The other saw the images in the evening first, and then again the next morning, after a night's sleep. 

The group that slept reacted less emotionally to the images the second time around than the group that didn't sleep. This came from reports of how they felt, and activity in the amygdala, an area of the brain associated with emotions. What's more, within the sleep group, the quality of the previous night's REM sleep was directly related to the emotional muting: the better they slept, the less emotional the memories became. 

Walker believes that REM sleep allows the brain to re-process disturbing memories, making them more factual and less painful. He notes that during REM sleep, stress-related hormones like norepinephrine decrease, and suspects that repackaging the memories without the influence of these hormones helps soothe their emotional sting. Other evidence for this comes from a veterans' hospital in Seattle, where patients who happened to take a certain blood pressure drug showed improvements in PTSD. It turned out that the blood pressure drug had a side effect of reducing norepinephrine levels in the brain. It's hoped that by understanding this process better, doctors will someday be able to help PTSD patients make peace with their memories again.

Now try and answer these questions:

  1. What is REM sleep? How does it relate to this study?
  2. What was the study's key conclusion? What evidence from the experiment supports that conclusion? What evidence from outside the experiment supports it?
  3. Why might it be useful for the brain to re-process memories in this way?
  4. Suppose the group that had not slept during the 12-hour period had the same decrease in emotional response to the images as the group that did sleep. What would that have suggested?

You may want to check out the December 2, 2011, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: Could dreaming help heal emotional wounds?, the relationship between the placebo effect and chronic pain, and new research into the genetics of empathy. Also included: a computer program to help prevent depression in girls, and exploring sex differences in mood disorders.

In the Science Update Memory Tagging, you'll hear how the brain may "tag" certain experiences for long-term storage during sleep.

In the Science NetLinks lesson Adolescent Sleep, students discuss, summarize, and express alternative positions regarding a study on adolescent sleep.


Going Further


For Educators

In the Science Update lesson Memory Tagging, you'll hear how the brain may "tag" certain experiences for long-term storage during sleep.

In the Science NetLinks lesson Adolescent Sleep, students discuss, summarize, and express alternative positions regarding a study on adolescent sleep.


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