Scientists have used scans to shed more light on how the brain deals with the memory of unpleasant or traumatic events during sleep.
The University of California, Berkeley team showed emotional images to volunteers, then scanned them several hours later as they saw them again.
Those allowed to sleep in between showed less activity in the areas of the brain linked to emotion.
Instead, the part of the brain linked to rational thought was more active.
Most people have to deal with traumatic events at some point in their lives, and, for some, these can produce post-traumatic stress disorder (PTSD)， leaving them emotionally disturbed long after the event itself.
There is significant evidence that the 20 percent of sleep in which we dream, also called REM sleep, plays a role in the processing of recent memories, and researchers believe that better understanding of this could eventually help PTSD patients.
Dr Matthew Walker, who led the study, said: "We know that during REM sleep there is a sharp decrease in norepinephrine, a brain chemical associated with stress.
"By reprocessing previous emotional experiences in this neurochemically 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."
據(jù)英國(guó)廣播公司11月24日?qǐng)?bào)道，科學(xué)家利用掃描儀放射出更多光線，探究出人腦在睡眠時(shí)是如何處理不愉快或創(chuàng)傷性事件所留下的記憶。
加州大學(xué)伯克利分校的科研小組向志愿者展示了一些有關(guān)情感的圖片。然后在幾個(gè)小時(shí)后再見到他們時(shí)重新掃描了他們的大腦圖像。
那些在兩次掃描之間被允許睡覺的人，大腦中聯(lián)系情感的這一區(qū)域相對(duì)不是那么活躍。
反之，他們大腦中有關(guān)理性思考的區(qū)域則更加活躍。
大部分人在生活中的某些時(shí)刻總要應(yīng)對(duì)一些創(chuàng)傷性的事件，這會(huì)導(dǎo)致一些人產(chǎn)生創(chuàng)傷后應(yīng)激障礙(PTSD)，使他們?cè)谑录旧硪呀?jīng)過去之后的很長(zhǎng)一段時(shí)間里，情感上仍然受到困擾。
有明確的證據(jù)表明，在我們會(huì)做夢(mèng)的睡眠時(shí)間，也就是REM睡眠(快速眼球運(yùn)動(dòng)rapid eyes movement,是一個(gè)睡眠的階段，眼球在此階段時(shí)會(huì)快速移動(dòng)，多數(shù)在醒來后能夠回憶的栩栩如生的夢(mèng)都是在REM睡眠發(fā)生的)階段中，有20%對(duì)處理近期記憶有非常重要的作用，研究人員認(rèn)為更好地理解這一點(diǎn)最終能夠幫助到PTSD的患者。
這項(xiàng)研究的領(lǐng)導(dǎo)者馬修•沃克博士說：“我們都知道，在REM睡眠階段，去甲腎上腺素會(huì)急劇下降，而去甲腎上腺素是大腦中一種與壓力有關(guān)的化學(xué)物質(zhì)。”
“在REM睡眠階段這種去甲腎上腺素水平較低的神經(jīng)化學(xué)的安全環(huán)境中，我們的大腦會(huì)對(duì)之前的情感經(jīng)歷進(jìn)行再加工，這樣我們?cè)诘诙煨褋頃r(shí)，那些經(jīng)歷的情感力度已經(jīng)軟化了。”
“我們會(huì)覺得好多了，自己能應(yīng)付得來。”