Robert Stickgold on Sleep, Memory and Dreams: Fitting the Pieces Together (Transcript)

Robert Stickgold

Here is the full transcript of professor Dr. Robert Stickgold’s TEDx Talk on Sleep, Memory and Dreams: Fitting the Pieces Together at TEDxRiverCity conference. Dr. Stickgold is the Director of Harvard’s Center for Sleep and Cognition.


This talk is basically about what sleep is doing for us. There’s this common belief that when you are asleep, the brain shuts off, the body lies down and nothing happens. And that’s really not what’s going on. It’s a little bit like a fairy tale, and in fact, “The Elves and the Shoemaker” fairy tale is about my story tonight.

So, here’s the story: The shoemaker was a poor shoemaker, had just enough leather left for one pair of shoes. He cut out the leather for two pairs of shoes – excuse me – and then, as it was late, he left the pieces on the bench, ready to sew in the morning. But when morning came, two pairs of shoes lay on the bench, most beautifully made and no sign of any one who had been there.

What I want to tell you is that this is not a fairy tale. This is what happens for us each and every night. And that sleep, in fact, is sewing together the pieces of our memory. I’m going to walk you through four examples of this, just to show you how powerful it is. I’m going to show you how, when you sleep, your brain will extract from experiences the gist of what happened – it will extract the gist and kind of forget all those details that weren’t so important.

It’ll discover the rules of our lives. It will take large amounts of experiences and take them all together and figure out what the rules are that explain how our worlds work. It will foster insight; it will let us come up with those insights that are so critical and so powerful – and so exciting when we have them.

And dreaming, in fact, is probably part of this entire process, and I’ll show you some new findings that suggest that that’s true. So, let’s start with the idea of sleep extracting the gist. In this study, we had subjects listen to lists of words spoken to them. Imagine you’re in a room – and here are the instructions: you are going to hear a series of words, broken up into lists of about a dozen words each. We want you to remember the words because later on we’ll give you a blank piece of paper and ask you to write down all the words you can remember.

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Now, I’ll give you an idea of what that feels like by taking you through one of those lists. Now, there’s going to be a test at the end, okay? And you are going to have to raise your hands. So, I’m going to give you a lesson in medicine. On the back of the arm, there’s a muscle, which is an extensor muscle that makes the arm go out, okay? This is not raising your hand. This is not raising your hand. You have to use that muscle and actually lift your hand because we are doing the experiment now.

Here’s the instructions: Watch these words as they go by. Remember them. You are going to be tested on them. [nurse] [sick] [lawyer] [medicine] [health] [hospital] [dentist] [physician] [ill] [patient] [office] [stethoscope] [cotton] Aaah – that’s not supposed to happen. Okay, end of list.

Normally, subjects would hear about a dozen of these lists and then be tested for recall. They would then come back, maybe twenty minutes later or maybe twelve hours later, and be tested on them. We’re going to do it now. If you saw each of these words, raise your hand, okay? [nurse] If you did see it. Okay? [sick] Lots of yeses. A lot of weak extensor muscles. Okay? Cotton, you see cotton? No, okay, nobody for cotton. [table] I don’t know why that plus is in the middle.

Doctor? Don’t say it, they were going to raise their hands. So, if I had done this competently, about half of you would have raised your hand for doctor, and you do that because the list is a gimmick list – we’ve put together a whole bunch of words related to doctor, but we don’t include the word “doctor” in the list. And it turns out, that about half of you will falsely remember that you saw the word “doctor” because your brain is busy extracting the gist of the list.

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So, we asked the question if, instead of testing you right away, and we would have you write down those words, if you had to come back twelve hours later and do it, how much would you forget? And the question is what happens if we train you in the morning and test you in the evening, compared to training you in the evening and testing you the next morning, after a night of sleep?

So, what difference does sleep make to that kind of memory? Well, the first thing you see is that across the day or the night you forget somewhere between 25% and 45% of the words that you would have remembered, based on other subjects, after just 20 minutes, and you actually forget less over the night – so, that’s the important factor. You will remember more of this list if you’ve slept on it than if you’ve gone through your day after you first see it.

But that’s the words you actually saw. What happens to those words that you didn’t see? Those gist words? Well, across the day, you still forget about 20% of them. But over a night of sleep, you actually get a bit better at it. It’s as if when you sleep, your brain is figuring out what it’s about. It’s holding on to that information, and it’s throwing out all the rest.

So, over a series of a days, in fact, what we see is that all that people remember are those words that weren’t on the list because you’ve extracted that gist, and that’s what you hold on to. And as we do that in life, it looks like it’s sleep, not waking, that allows us to extract that gist. So, when we figure out what the take-home message is, we do it in our sleep.

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Now, interestingly, subjects also come up with words that weren’t on the list and weren’t the gist words either. So, they come up with words like “blood,” which is probably from that doctor list. They think of it because of that. Someone else came up with the word “plate,” and you can see one of the lists was about cups. Or “spoon” when one of the lists was about cups. That’s pretty common when you do this study. But with this 12-hour interval, we started to see funny words popping up, like “fuzzy”. I mean, where did that come from? And we thought maybe from “rough” or from the list of words about soft, but it’s really not either of those. And we get the word “swirl”. Where did that come from?

And Jessica Payne, my student, said, “Well, maybe it came from ‘mountain,’ like they were imagining clouds or soft, like some swirly soft fabric.” But then some other people said, “Well, no, maybe it’s cup – like, you know, you swirl your coffee, or chair – you swirl your chair.” And it started to feel like what these people are doing is they are coming up with words that don’t just epitomize one list but are now sort of starting to bring all the lists together.

And when she looked, she finds out you’re not getting those creative intrusions, so much, when you’re awake, you’re getting them when you’re asleep. So, again, it’s when you’re sleeping that the brain is doing this work of pulling everything together and seeing how it fits together and how to summarize it.

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