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."
据英国广播公司11月24日报道，科学家利用扫描仪放射出更多光线，探究出人脑在睡眠时是如何处理不愉快或创伤性事件所留下的记忆。
加州大学伯克利分校的科研小组向志愿者展示了一些有关情感的图片。然后在几个小时后再见到他们时重新扫描了他们的大脑图像。
那些在两次扫描之间被允许睡觉的人，大脑中联系情感的这一区域相对不是那么活跃。
反之，他们大脑中有关理性思考的区域则更加活跃。
大部分人在生活中的某些时刻总要应对一些创伤性的事件，这会导致一些人产生创伤后应激障碍(PTSD)，使他们在事件本身已经过去之后的很长一段时间里，情感上仍然受到困扰。
有明确的证据表明，在我们会做梦的睡眠时间，也就是REM睡眠(快速眼球运动rapid eyes movement,是一个睡眠的阶段，眼球在此阶段时会快速移动，多数在醒来后能够回忆的栩栩如生的梦都是在REM睡眠发生的)阶段中，有20%对处理近期记忆有非常重要的作用，研究人员认为更好地理解这一点最终能够帮助到PTSD的患者。
这项研究的领导者马修•沃克博士说：“我们都知道，在REM睡眠阶段，去甲肾上腺素会急剧下降，而去甲肾上腺素是大脑中一种与压力有关的化学物质。”
“在REM睡眠阶段这种去甲肾上腺素水平较低的神经化学的安全环境中，我们的大脑会对之前的情感经历进行再加工，这样我们在第二天醒来时，那些经历的情感力度已经软化了。”
“我们会觉得好多了，自己能应付得来。”
