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It's MORNING EDITION from NPR News. Good morning. I'm David Greene.

STEVE INSKEEP, HOST:

And I'm Steve Inskeep.

It's Monday, time for Your Health. We spend a lot of time trying to remember things - names, errands, where we left our keys and something else. I can't quite recall. Anyway, we also spend a lot of time cursing our tendency to forget. And today in Your Health, NPR's Alix Spiegel reports on research that turns the tables on our traditional views about remembering and forgetting. Her story starts at a memory competition.

NELSON DELLIS: Four of spades.

UNIDENTIFIED MAN: OK.

RON WHITE: Seven of diamonds.

UNIDENTIFIED MAN: Got it.

ALIX SPIEGEL, BYLINE: The 2012 US Memory competition that happened in March started around 8 in the morning and by 3 in the afternoon - the reigning champion Nelson Dellis had memorized 303 random numbers, 162 unknown names and faces, and 24 lines of poetry. And so Dellis sat on stage next to his very last competitor, a man named Ron White. Both had been given five minutes to commit to memory the order of 2 decks of shuffled cards. It was the very final event, and they were taking turns, calling out one card after another.

DELLIS: Three of hearts.

UNIDENTIFIED MAN: OK. Ronnie, back to you.

WHITE: I believe it's the five of diamonds?

DELLIS: You got it.

SPIEGEL: Each of these men had trained diligently, had spent hours and months and years practicing these very specific techniques which improved their ability to remember. And the audience in the room was packed with people who shared their enthusiasm for remembering. People who found it thrilling and hung on every word until finally, Ron White made a fatal misstep.

WHITE: The seven of clubs.

(SOUNDBITE OF GROANS)

(APPLAUSE)

SPIEGEL: We as a culture celebrate remembering. And Malcolm MacLeod, a memory researcher at the University of St Andrews in Scotland, says probably for good reason.

MALCOLM MACLEOD: In terms of our every day lives, we're always being asked for information - people's telephone numbers or vehicle license plates or birthdays.

SPIEGEL: So it's no surprise that in MacLeod's line of work there's a lot of focus on memory and how to improve it.

MACLEOD: Forgetting on the other hand, I think has tended to be characterized in terms of this thing that you - that you don't really want to engage in.

SPIEGEL: But about 10 years ago MacLeod got interested in forgetting. Specifically, he wanted to know if people could learn to forget in the same way that memory competitors learned to remember. What would happen if you actually sat down and practiced forgetting something - intentionally?

MACLEOD: Intentional forgetting is really about a memory that already exists. It's already there. And it's about preventing it coming to mind.

SPIEGEL: Now there already had been some research on this kind of intentional forgetting. In 2001, a researcher had shown that you could teach people to forget simple things, like two words that had been paired together. But MacLeod wondered if intentional forgetting could also be used with autobiographical memories - events in people's actual lives. He and his co-researcher - a woman named Saima Noreen - suspected it couldn't.

SAIMA NOREEN: No, to put it simply...

MACLEOD: Because autobiographical memory is so vivid, it's so rich, that it's going to be incredibly difficult to keep from mind those sorts of events that you've personally experienced.

SPIEGEL: To be clear, the intentional forgetting that interested MacLeod and Noreen is totally different from unintentional forgetting, which we do all the time - forgetting to buy milk at the store for instance. Instead, MacLeod and Noreen were interested in personally significant memories and what would happen if you systematically tried to forget them.

They figured that learning to forget could potentially help people, like with depression or maybe even post-traumatic stress disorder. And so they invited a bunch of people into their lab and began their experiments by giving them different a series of different words.

MACLEOD: So our subjects came in and...

NOREEN: In the first part of the experiment people saw a word, and they were told to generate a specific memory in response to that word. So try and come up with a memory.

MACLEOD: We said, for example...

NOREEN: Barbeque, theater, occasion, wildlife...

SPIEGEL: These are some of the actual memory stimulating words Noreen and MacLeod gave to their actual subjects. There were 24 in all and for each word participants generated one personally significant memory. About a week later, subjects were invited back into the lab and given a full transcript of each of the memories they'd share, along with the word that had generated it.

They reviewed that until they knew exactly which word went with which memory. Then they were told every time you see the word associated with a memory in green, speak the memory out loud. But every time you see the word associated with a memory in red...

NOREEN: For the red, they're told it's very important that they try not to say or think about the memory that's associated with that word.

SPIEGEL: Noreen and MacLeod showed the subjects 16 of the 24 words over and over and over and over, and each time the subjects either repeated the memory or blocked it; some apparently just made their minds blank, others distracted themselves with other thoughts. At the end of this process, the subjects were tested to see whether there was a change in what they recalled. And there was - in the memories that had been repeatedly blocked.

MACLEOD: A significant forgetting effect, about a 12 percent drop in the level of details recalled. That's a large effect.

SPIEGEL: What's interesting though is which part of the memories were forgotten?

To understand, listen to Noreen read this transcript based on one of the actual memories in the study. It involves a girl getting a new pair of very short pants from her mother.

NOREEN: The cause of the event was me wearing a new pair of trousers that my mom had bought for me for secondary school when I first started. The consequence of the event was that at lunch time when I went to t he bathroom, an older girl started making fun of me for having short trousers. It was the first time I felt uncomfortable with what I was wearing. It made me feel very self-conscious and I hated that.

SPIEGEL: So that was the original memory, but after blocking the memory again and again and again, certain details began to fall away.

Now, it's not that she forgot what happened, Noreen says, instead she began to lose the personal meaning associated with that memory.

NOREEN: The fact that she said, it was the first time I felt uncomfortable with what I was wearing. And she also forgot she said, that it made her feel very self-conscious and she hated that.

SPIEGEL: So she forgot about the kind of emotional pain it cost?

NOREEN: Yeah. That's what we've typically found like the actual personal meaning tends to be more susceptible to being forgotten.

SPIEGEL: This, Noreen says, is probably because what a memory means is usually derived after the event takes place. And though, when you tell someone your memory, it seems like it's part of the memory itself, personal meaning often changes.

NOREEN: Obviously, something negative happened but you're in a happy place now, then you might interpret that negative event as being not positive, but at the same time, potentially leading to where you are now so you can see positive in that event. So again, you're always deriving different meanings from the same event.

SPIEGEL: And because that part of our memory shifts, it's less secure. At least that's their theory. They also don't know how long this forgetting effect will last. It might evaporate over time.

But the biggest question, of course, is whether this work will ever have practical applications. Will - one day - we know so much about forgetting that we'll actually be able to train ourselves to forget? Noreen and Macleod say it's way too early to tell. But they obviously can both see ways that particular skill could be helpful.

Have you ever tried to forget something?

NOREEN: I think every one's probably tried to forget something.

SPIEGEL: What's the thing you wanted to forget.

(LAUGHTER)

NOREEN: I don't think that's probably, I don't think that's probably worth mentioning.

SPIEGEL: We all have decisions - things in our past - that we would like to forget. Noreen and Macleod believe that our capacity to forget, is as important and interesting, as our ability to remember.

Alix Spiegel, NPR News, Washington.

(SOUNDBITE OF MUSIC)

INSKEEP: It's MORNING EDITION from NPR News.

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