While You Were Sleeping

“Imagine that you wake up in the morning feeling nothing special, yet you find yourself inexplicably behaving just a bit differently during the day. For example, you take a sniff every time you hear a tone,” says Prof. Noam Sobel. Of course, the people this actually happened to knew they had volunteered for a sleep experiment in Sobel’s lab. They knew that their sleep patterns had been closely monitored. But they had no recall, whatsoever, of the “lesson” they had learned while snoring peacefully. It was the sniffing that gave it away: While asleep, they had undergone conditioning to associate tones with smells. The next day, when the now awake volunteers heard the tones, their unconscious sniffs revealed whether they have been conditioned to associate the tone with a nice smell or a nasty one.

This may be the first incontrovertible demonstration of sleep learning in human adult brains. The trick, says Anat Arzi, a PhD student in Sobel’s group who led the project, was to find the right teaching method.

image: Thinkstock

Tests of verbal learning (think of the old tape recorder-under-the-pillow experiments) had pretty much ruled this out as way to absorb lessons painlessly in one’s sleep. And the results of other experiments either suggested that the subjects had briefly woken during the trials, or else they took place during unnatural sleep, with the subjects drugged to make sure they stayed out for the duration. So, on the one hand, years of sleep learning research had left the question up in the air and tending toward falling on the side of nonexistence. But on the other hand, a number of recent studies have suggested a close connection between sleep and learning and memory consolidation. “In spite of all the previous research, we thought that some kind of sleep learning should be possible,” says Arzi. “The question was: which kind?”

Tones and smells turned out to be ideal: They don’t wake the sleepers, yet they are sensed during sleep. And sniffing – the reflexive response to the odors – occurs whether one smells them asleep or awake. That meant that instead of relying on reported memories, the researchers only had to watch for the long, deep sniff we automatically take when we smell a good smell, or the short, shallow one associated with a bad smell to know that the subjects had been conditioned to associate a tone with a particular odor.

What’s next? Sobel and Arzi found that the conditioning is best retained when it takes place during non-REM sleep – the same sleep stage in which the things learned during the day get consolidated into memory. So there is an intriguing connection there that they want to explore. And, while we’ll never be able to study for that physics exam in our sleep, finding proof for one type of sleep learning suggests that others might be possible.


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Really cool study! No links though? Didn't see it in Pubmed, so I guess it's not yet published. I was interested to see how many subjects they tested, how they scored the 'unconscious sniffing' (e.g. was the scorer blinded?), etc. I wanted to get a better sense (har!) of how robust the findings are.

Just published in Nature Neuroscience this second.

Trully nice article!! And promising indeed..!!

I hope someday soon to find how we can learn more things while sleeping or how to slow down time to learn things faster by more repetition in the same time ;)

On the exploration/conquest of the brain/mind realm:

I thought REM sleep was where memory consolidation was supposed to occur...

By Chris Leithiser (not verified) on 27 Aug 2012 #permalink

Both appear to play a role, but the slow-wave, non-REM sleep seems to be critical.

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By Dr. Vineet Sag… (not verified) on 29 Aug 2012 #permalink

Very nice article! I'm gonna share this to my friends. One of the topics that we always talk about is how the kind or quality of sleep affect our intelligence.Thanks for the post!

Im doing a report on anat arzi so, is arzi a male or female?

Another study to look forward too because it can contribute a lot and will give a big impact in improving our health and well being.

By west perth chi… (not verified) on 10 Oct 2012 #permalink