邊睡邊學，可能嗎？

巴哈爾·戈利普爾

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？”

但近年來，多項研究發現，睡眠中的大腦并非完全一團漿糊。這些研究表明，睡眠中的大腦不僅有可能汲取信息，甚至還有可能形成新的記憶。但問題是，這些記憶要么是暗示性的，要么是無意識的。換句話說，這種形式的學習極為初級，和學德語或量子力學時大腦要完成的那些工作相比，實在太過簡單。

雖然如此，這些發現讓睡眠學習不再是癡心妄想，使其重回科學家的視野。

“幾十年來科學文獻一直在否認睡眠學習的可能。因此，即便是發現最初級的睡眠學習，也足以引起科學家的興趣，”澳大利亞墨爾本的莫納什大學的神經科學家托馬·安德里永說，“但人們不會對這種初級學習形式產生真正的興趣。”

安德里永還向科學鮮聞網指出，最近的這些發現為科學家帶來了將睡眠學習用于相關領域的希望。例如，睡眠學習的暗示性本質可能有助于人們擺脫抽煙等壞習慣，或者形成新的好習慣。

臭雞蛋與抽煙：聯系的建立

多項研究表明，在睡眠期間可能存在某種名為“條件作用”的初級學習。例如，在發表于期刊《自然·神經科學》的一項2012年研究中，一些以色列研究者發現，人們在睡眠中可以學會建立聲音與氣味之間的聯系。科學家在對睡眠學習受試者播放某種聲音的同時，釋放出一種類似臭魚的難聞氣味。醒來后，受試者一聽見同樣的聲音，就預感臭味將至，進而屏住了呼吸。

“研究結果清晰地表明，人類可以在睡眠中形成新的記憶。”安德里永說。他本人并未參與該項研究。

在發表于《神經科學學報》的一項2014年研究中，研究者發現，雖然這種記憶只是暗示性的，但它可能影響人們的行為。在該研究中，抽煙者在混合著煙味與臭雞蛋味或臭魚味的環境中睡了一夜之后，抽煙數量有所下降。

guga的意思是大象：睡夢之中學外語？

安德里永及其同事發現，睡眠學習未必局限于簡單的條件作用。在他們發表于《自然·通訊》的一項2017年研究中，受試者能夠正確選出那些曾在睡眠中聽過的復雜聲音組合。

不僅如此，人在睡眠中的學習能力還可能擴至單詞學習。在一項發表于期刊《當代生物學》的研究中，研究者將一些臆造詞連同它們所謂的含義成對地播放給睡眠中的受試者，如guga及其含義“大象”這樣的組合。待他們醒來后，讓他們從多個選項中指出臆造詞的正確含義。結果顯示，這些受試者的正確率高于隨機水平。

上述研究的共性在于，它們都體現出某種以暗示形態存在的記憶。“它并非某種可以自然而然地加以運用的知識，因為受試者根本就意識不到它的存在。”安德里永說，“問題是，‘我們的研究該如何繼續？”

學習一門新語言涉及多個不同的層面，如識別聲音、記憶詞匯和掌握語法。截至目前，研究表明，在睡眠中去熟悉一門語言的語音、語調，甚至詞義，都是有可能的。但與我們白天不知不覺中一直在進行的那種學習相比，這種學習層次較低。

還有一個因素不得不考慮，那就是代價，安德里永提醒道。他說，用新信息來刺激睡眠中的大腦有可能擾亂睡眠功能，從而對白天所學內容的整理與鞏固產生負面影響。

雖然以犧牲睡眠質量為代價來學幾個單詞有些得不償失，但有關睡眠學習的研究仍在繼續，因為在特殊情況下，這種犧牲可能是值得的。例如，在人們需要改變某種習慣，或罹患恐懼癥及創傷后應激障礙，需要改寫令人煩惱而又揮之不去的記憶時，就可能用到睡眠學習。

對上述情形可能有用的某些暗示性學習在睡眠中效果更為顯著。例如，在上文提到的借臭雞蛋味減少抽煙的研究中，如果受試者處于清醒狀態，該條件作用則不起效。如果你每天都在垃圾桶旁抽煙，就會明白臭雞蛋味和煙味之間并無聯系，也就不會在大腦中將其關聯。我們醒著的時候可沒那么好騙。

“但睡眠中的大腦就沒那么聰明了，可以操縱它為我們所用。”安德里永說，“這聽起來和電影《美麗心靈的永恒陽光》里的情形很像。雖然研究還在進行中，但操縱記憶的可能性已然存在。”

在那一天到來之前，請別忘了，最好的睡眠學習還是睡個好覺。

（譯者為“《英語世界》杯”翻譯大賽獲獎者; 單位：華北水利水電大學外國語學院）