It turns out that nodding off in class may not be such a bad idea after all, as a new study has shown that going to sleep shortly after learning new material is the best way to remember it.

According to US lead author Jessica Payne, a psychologist at the University of Notre Dame in Indiana, nodding off after learning something new is like ‘telling’ the sleeping brain what to retain. Along with colleagues, she studied 207 students who habitually slept for at least six hours per night. Participants were randomly assigned to study declarative, semantically related or unrelated word pairs at 9am or 9pm, and returned for testing 30 minutes, 12 hours or 24 hours later.

Declarative memory refers to the ability to consciously remember facts and events, and can be broken down into episodic memory (memory for events) and semantic memory (memory for facts about the world). People routinely use both types of memory every day – recalling where we parked today or learning how a colleague prefers to be addressed. At the 12-hour retest, memory overall was superior following a night of sleep compared to a day of wakefulness. At the 24-hour retest, with all subjects having received both a full night of sleep and a full day of wakefulness, subjects` memories were superior when sleep occurred shortly after learning, rather than following a full day of wakefulness.

‘Our study confirms that sleeping directly after learning something new is beneficial for memory. What`s novel about this study is that we tried to shine light on sleep`s influence on both types of declarative memory by studying semantically unrelated and related word pairs,’ Payne said.‘Since we found that sleeping soon after learning benefited both types of memory, this means that it would be a good thing to rehearse any information you need to remember just prior to going to bed. In some sense, you may be “telling” the sleeping brain what to consolidate.’

Results of the study were published on March 22 in PLOS One.

看来在课堂上打瞌睡也许并不是坏事。一项新研究显示，学完新知识后马上打个小盹是最佳的记忆方法。

该研究的主要作者、美国印第安纳州诺特丹大学的心理学家杰西卡•佩恩认为，在学完新东西后打个盹就像把要记住的东西“告诉”睡眠中的大脑。她和同事一起对207名学生进行了研究，这些学生习惯每晚至少睡六个小时。参与者被随机分配到几个学习小组，学习内容是陈述性知识，包括语义相连或不相连的词组。学习时间在早上9点或晚上9点。学完后他们在30分钟、12小时或24小时后回来做测试。陈述性记忆指的是有意识地记忆事实和事件的能力，可以分为情节记忆(对事件的记忆)和语义记忆(对事实类知识的记忆)。人们每天都会例行运用这两种记忆——回想今天我们把车停在了哪里或了解一个同事喜欢别人怎么称呼他。在12小时后再次进行测试时，总体来看睡了一夜的人相比还没睡觉的人记忆效果更好。在24小时后再度测试时，所有的实验对象都睡了一整夜，也在清醒中度过了一个白天。这次，那些在学习后不久就入睡的人比那些学习后过了一整个白天才睡觉的人记忆效果更好。

佩恩说：“我们的研究证实，在学习新东西后马上睡觉对记忆有帮助。这项研究的创新之处在于，我们试图通过对语义相连和不相连的词组的记忆研究来揭示睡眠对于两种陈述性记忆的影响。”“我们发现在学习之后很快就睡觉对两种记忆都有帮助，这意味着在上床睡觉前温习你要记忆的东西将很有好处。在某种意义上，你可能在‘告诉’睡眠中的大脑需要巩固强化的记忆。”