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Dream sleep takes sting out of painful memories

They say time heals all wounds, and new research from the University of California, Berkeley, indicates that time spent in dream sleep can help us overcome painful ordeals.

UC Berkeley researchers have found that during the dream phase of sleep, also known as REM sleep, our stress chemistry shuts down and the brain processes emotional experiences and takes the edge off difficult memories.

The findings offer a compelling explanation for why people with post-traumatic stress disorder (PTSD), such as war veterans, have a hard time recovering from distressing experiences and suffer reoccurring nightmares. They also offer clues into why we dream.

“The dream stage of sleep, based on its unique neurochemical composition, provides us with a form of overnight therapy, a soothing balm that removes the sharp edges from the prior day’s emotional experiences,” said Matthew Walker, associate professor of psychology and neuroscience at UC Berkeley and senior author of the study to be published this Wednesday, Nov. 23, in the journal Current Biology.

(UC Berkeley)
(UC Berkeley)

For people with PTSD, Walker said, this overnight therapy may not be working effectively, so when a “flashback is triggered by, say, a car backfiring, they relive the whole visceral experience once again because the emotion has not been properly stripped away from the memory during sleep.”

The results offer some of the first insights into the emotional function of Rapid Eye Movement (REM) sleep, which typically takes up 20 percent of a healthy human’s sleeping hours. Previous brain studies indicate that sleep patterns are disrupted in people with mood disorders such as PTSD and depression.

While humans spend one-third of their lives sleeping, there is no scientific consensus on the function of sleep. However, Walker and his research team have unlocked many of these mysteries linking sleep to learning, memory and mood regulation. The latest study shows the importance of the REM dream state.

“During REM sleep, memories are being reactivated, put in perspective and connected and integrated, but in a state where stress neurochemicals are beneficially suppressed,” said Els van der Helm, a doctoral student in psychology at UC Berkeley and lead author of the study.

Thirty–five healthy young adults participated in the study. They were divided into two groups, each of whose members viewed 150 emotional images, twice and 12 hours apart, while an MRI scanner measured their brain activity.

Half of the participants viewed the images in the morning and again in the evening, staying awake between the two viewings. The remaining half viewed the images in the evening and again the next morning after a full night of sleep.

Those who slept in between image viewings reported a significant decrease in their emotional reaction to the images. In addition, MRI scans showed a dramatic reduction in reactivity in the amygdala, a part of the brain that processes emotions, allowing the brain’s “rational” prefrontal cortex to regain control of the participants’ emotional reactions.

In addition, the researchers recorded the electrical brain activity of the participants while they slept, using electroencephalograms. They found that during REM dream sleep, certain electrical activity patterns decreased, showing that reduced levels of stress neurochemicals in the brain soothed emotional reactions to the previous day’s experiences.

“We know that during REM sleep there is a sharp decrease in levels of norepinephrine, a brain chemical associated with stress,” Walker said. “By reprocessing previous emotional experiences in this neuro-chemically safe environment of low norepinephrine during REM sleep, we wake up the next day, and those experiences have been softened in their emotional strength. We feel better about them, we feel we can cope.”

Walker said he was tipped off to the possible beneficial effects of REM sleep on PTSD patients when a physician at a U.S. Department of Veterans Affairs hospital in the Seattle area told him of a blood pressure drug that was inadvertently preventing reoccurring nightmares in PTSD patients.

It turns out that the generic blood pressure drug had a side effect of suppressing norepinephrine in the brain, thereby creating a more stress-free brain during REM, reducing nightmares and promoting a better quality of sleep. This suggested a link between PTSD and REM sleep, Walker said.

“This study can help explain the mysteries of why these medications help some PTSD patients and their symptoms as well as their sleep,” Walker said. “It may also unlock new treatment avenues regarding sleep and mental illness.”

Other co-authors of the study are UC Berkeley sleep researchers Justin Yao, Shubir Dutt, Vikram Rao and Jared Saletin. (Provided by UC Berkeley)



REM 수면, 아픈 기억 완화시켜

수면 중 꿈을 꾸는 구간인 급속안구운동(REM: r apid eye movement) 수면이 아픈 기억을 누그러뜨리는 기능을 수행한다는 연구결과 가 나왔다.

미국 버클리 캘리포니아 대학 심리학과의 엘스 반 데르 헬름(Els van der Helm) 연구원은 REM 수면에서는 뇌의 스트레스 시스템이 폐쇄된 상태에서 감정적 경험들이 처리되며 이를 통해 기억들의 아픈 부분들이 잘려나간다는 새로운 사실이 밝혀졌다 고 말한 것으로 영국의 데일리 메일 인터넷판과 과학뉴스 포털 피조그 닷컴(Physorg .com)이 23일(현지시간) 보도했다.

그의 연구팀은 건강한 청년 35명을 두 그룹으로 나누어 한 그룹에겐 감정반응을 유발하는 150가지 영상을 아침에 보여주고 12시간이 지난 뒤인 저녁에 다시 보여주 었다. 다른 그룹에겐 같은 영상을 저녁에 보여주고 자고난 다음날 아침 다시 보여주 었다. 다만 이 두번째 그룹은 수면 중 자기공명영상(MRI)과 뇌파도(EEG)로 뇌의 움 직임을 관찰했다.

두번째 그룹은 자고난 뒤 아침에 다시 영상들을 보여주었을 때 전날 저녁 같은 영상을 보았을 때보다 감정반응의 강도가 현저히 줄어든 것으로 나타났다.

이 그룹은 MRI 영상에서도 감정을 처리하는 뇌부위인 편도(扁桃)의 반응이 크게 줄어든 것으로 밝혀졌다. 이들은 뇌파도에서도 REM 수면 중 특정 전기활동 패턴이 줄어든 것으로 나타났다.

이는 뇌의 스트레스 관련 신경전달물질이 감소하면서 전날 경험한 것에 대한 감 정반응이 누그러졌음을 보여주는 것이다.

연구팀을 지도한 매슈 워커 신경과학교수는 REM 수면 중에는 스트레스와 관련된 신경전달물질인 노르에피네프린이 크게 감소한다고 밝히고 이처럼 안전한 상태에서 전날의 감정경험이 재처리되기 때문에 감정반응의 강도가 누그러져 아침에 잠이 깨

면 그 감정을 더 잘 감당할 수 있게 된다고 설명했다.

수면은 크게 REM 수면과 비REM 수면으로 구성되며 둘 모두 건강을 유지하는 데 필요하다.

전체 수면 중 약20%를 차지하는 REM 수면은 꿈을 꾸는 구간으로 뇌는 활성화되고 근육은 마비상태가 된다. 비REM 수면 중에는 신체조직이 수리되고 세포가 재생되며 면역기능이 강화되는 것으로 알려져 있다.

이 연구결과는 '현대 생물학(Current Biology)' 최신호에 실렸다. (연합뉴스)


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