巴哈尔·戈利普尔

There are only 24 hours in a day， and usually about a third of that is spent sleeping. So， the overambitious have always wondered： Is it possible to make use of this time and learn a new skill or even a language？ In other words， is sleep learning possible？

The answer is yes and no， depending on what we mean by “learning.”

Absorbing complex information or picking up a new skill from scratch by， say1， listening to an audio recording during sleep is almost certainly impossible. But research shows that the sleeping brain is far from idle and that some forms of learning can happen. However， whether thats worth losing sleep over has yet to be determined.

Sleep learning： From sham2 to science

The concept of sleep learning， or hypnopedia3， has a long history. The first study to demonstrate a memory and learning benefit from sleep was published in 1914 by German psychologist Rosa Heine. She found that learning new material in the evening before sleep results in better recall compared to learning during the day.

Thanks to many studies done since then， we now know that sleep is crucial for forming long-term memories of what we have encountered during the day. The sleeping brain replays the days experiences and stabilizes them by moving them from the hippocampus4， where they are first formed， to regions across the brain. Given that so much is happening to memories during sleep， its natural to ask if the memories can be altered， enhanced or even formed anew.

One popular approach to sleep learning was Psycho-phone5， a popular device in the 1930s. It played out motivational messages to sleepers， such as “I radiate love，” supposedly helping the people absorb the ideas in their subconscious and wake up with radiant confidence.

At first， it seemed that research backed up the idea behind devices like Psycho-phone. Some early studies found that people learned the material they encountered during sleep. But those findings were debunked6 in the 1950s， when scientists began to use EEG7 to monitor sleep brain waves. Researchers found that if any learning had happened， it was only because the stimuli had woken the participants. These poor studies launched sleep learning into the trash can of pseudoscience.

But in recent years， studies have found that the brain may not be a total blob8 during sleep. These findings suggest that it is possible for the sleeping brain to absorb information and even form new memories. The catch9， however， is that the memories are implicit， or unconscious. Put10 another way， this form of learning is extremely basic， much simpler than what your brain has to accomplish if you want to learn German or quantum mechanics.

Still， these findings have elevated sleep learning from the category of pipe dreams11 and put it back on scientists radar.

“For decades the scientific literature12 was saying sleep learning was impossible. So， even seeing the most basic form of learning is interesting for a scientist，” said Thomas Andrillon， a neuroscientist at Monash University in Melbourne， Australia. “But people are not really interested in this basic form of learning.”

For scientists， the recent discoveries have raised hopes about possible applications， Andrillon told Live Science13. For example， the implicit nature of sleep learning makes the phenomenon useful for people who want to shed a bad habit， like smoking， or form new good ones.

Rotten eggs and smoking： Making associations

Multiple studies have found that a basic form of learning， called conditioning， can happen during sleep. In a 2012 study published in the journal Nature Neuroscience， for example， Israeli researchers found that people can learn to associate sounds with odors during sleep. The scientists played a tone to sleeping study participants while unleashing a nasty spoiled-fish smell. Once awake， upon hearing the tone， the people held their breath in anticipation of a bad smell.

“This was a clear finding showing humans can form new memories during sleep，” said Andrillon， who was not involved in that study.

Although the memory was implicit， it could affect the peoples behavior， researchers found in a 2014 study published in the Journal of Neuroscience. In that research， smokers used fewer cigarettes after spending a night being exposed to the smell of cigarettes paired with rotten eggs or spoiled fish.

“Guga” means elephant： Learning languages during sleep？

Andrillon and his colleagues have found that learning in sleep can go beyond simple conditioning. In their 2017 study published in the journal Nature Communications， subjects were able to pick out complex sound patterns that they had heard during sleep.

Learning abilities in sleep may extend to the learning of words. In a study published in the journal Current Biology， researchers played pairs of made-up words and their supposed meanings， like that “guga” means elephant， to sleeping participants. After this， when awake， the people performed better than chance when they had to pick the right translation of made-up words in a multichoice test.

What all these studies have in common is that they show an implicit form of memory. “Its not some knowledge theyll be able to use spontaneously， because they dont know this knowledge is even there，” Andrillon said. “The question is， ‘Where do we go from there？”

但近年来，多项研究发现，睡眠中的大脑并非完全一团浆糊。这些研究表明，睡眠中的大脑不仅有可能汲取信息，甚至还有可能形成新的记忆。但问题是，这些记忆要么是暗示性的，要么是无意识的。换句话说，这种形式的学习极为初级，和学德语或量子力学时大脑要完成的那些工作相比，实在太过简单。

虽然如此，这些发现让睡眠学习不再是痴心妄想，使其重回科学家的视野。

“几十年来科学文献一直在否认睡眠学习的可能。因此，即便是发现最初级的睡眠学习，也足以引起科学家的兴趣，”澳大利亚墨尔本的莫纳什大学的神经科学家托马·安德里永说，“但人们不会对这种初级学习形式产生真正的兴趣。”

安德里永还向科学鲜闻网指出，最近的这些发现为科学家带来了将睡眠学习用于相关领域的希望。例如，睡眠学习的暗示性本质可能有助于人们摆脱抽烟等坏习惯，或者形成新的好习惯。

臭鸡蛋与抽烟：联系的建立

多项研究表明，在睡眠期间可能存在某种名为“条件作用”的初级学习。例如，在发表于期刊《自然·神经科学》的一项2012年研究中，一些以色列研究者发现，人们在睡眠中可以学会建立声音与气味之间的联系。科学家在对睡眠学习受试者播放某种声音的同时，释放出一种类似臭鱼的难闻气味。醒来后，受试者一听见同样的声音，就预感臭味将至，进而屏住了呼吸。

“研究结果清晰地表明，人类可以在睡眠中形成新的记忆。”安德里永说。他本人并未参与该项研究。

在发表于《神经科学学报》的一项2014年研究中，研究者发现，虽然这种记忆只是暗示性的，但它可能影响人们的行为。在该研究中，抽烟者在混合着烟味与臭鸡蛋味或臭鱼味的环境中睡了一夜之后，抽烟数量有所下降。

guga的意思是大象：睡梦之中学外语？

安德里永及其同事發现，睡眠学习未必局限于简单的条件作用。在他们发表于《自然·通讯》的一项2017年研究中，受试者能够正确选出那些曾在睡眠中听过的复杂声音组合。

不仅如此，人在睡眠中的学习能力还可能扩至单词学习。在一项发表于期刊《当代生物学》的研究中，研究者将一些臆造词连同它们所谓的含义成对地播放给睡眠中的受试者，如guga及其含义“大象”这样的组合。待他们醒来后，让他们从多个选项中指出臆造词的正确含义。结果显示，这些受试者的正确率高于随机水平。

上述研究的共性在于，它们都体现出某种以暗示形态存在的记忆。“它并非某种可以自然而然地加以运用的知识，因为受试者根本就意识不到它的存在。”安德里永说，“问题是，‘我们的研究该如何继续？”

学习一门新语言涉及多个不同的层面，如识别声音、记忆词汇和掌握语法。截至目前，研究表明，在睡眠中去熟悉一门语言的语音、语调，甚至词义，都是有可能的。但与我们白天不知不觉中一直在进行的那种学习相比，这种学习层次较低。

还有一个因素不得不考虑，那就是代价，安德里永提醒道。他说，用新信息来刺激睡眠中的大脑有可能扰乱睡眠功能，从而对白天所学内容的整理与巩固产生负面影响。

虽然以牺牲睡眠质量为代价来学几个单词有些得不偿失，但有关睡眠学习的研究仍在继续，因为在特殊情况下，这种牺牲可能是值得的。例如，在人们需要改变某种习惯，或罹患恐惧症及创伤后应激障碍，需要改写令人烦恼而又挥之不去的记忆时，就可能用到睡眠学习。

对上述情形可能有用的某些暗示性学习在睡眠中效果更为显著。例如，在上文提到的借臭鸡蛋味减少抽烟的研究中，如果受试者处于清醒状态，该条件作用则不起效。如果你每天都在垃圾桶旁抽烟，就会明白臭鸡蛋味和烟味之间并无联系，也就不会在大脑中将其关联。我们醒着的时候可没那么好骗。

“但睡眠中的大脑就没那么聪明了，可以操纵它为我们所用。”安德里永说，“这听起来和电影《美丽心灵的永恒阳光》里的情形很像。虽然研究还在进行中，但操纵记忆的可能性已然存在。”

在那一天到来之前，请别忘了，最好的睡眠学习还是睡个好觉。

（译者为“《英语世界》杯”翻译大赛获奖者; 单位：华北水利水电大学外国语学院）