Our days are full of things to remember, and they don't always arrive in an orderly fashion. Perhaps you begin your commute home and remember that you need to pick up milk. But then immediately, another to-do springs to mind: You never called back your friend last week. You may try to hold both in your head, but in the end the milk, the phone call or both still sometimes fall away, forgotten.
A new scientific model of forgetting is taking shape, which suggests keeping multiple memories or tasks in mind simultaneously can actually erode them.
Neuroscientists already knew that memories can interfere with and weaken each other while they are locked away in the recesses of long-term memory. But this new model speaks to what happens when multiple memories are coexisting front and center in our minds, in a place called "working memory."
It argues that when we let multiple memories come to mind simultaneously, those memories immediately lock into a fierce competition with each other. The milk and the phone call fight to each be remembered more than the other.
"When these memories are tightly competing for our attention the brain steps in and actually modifies those memories," says Jarrod Lewis-Peacock, a neuroscientist at UT Austin.
The brain crowns winners and losers. If you ended up remembering the milk and forgetting the phone call, your brain strengthens your memory for getting milk and weakens the one for phoning your friend back, so it will be easier to choose next time you're faced with that dilemma.
Previous research has demonstrated this competition-based weakening of memories over very short periods of time, but Lewis-Peacock and his colleagues recently put it to the test again, to see if it could cause long-term forgetting. They decided to force two memories to compete: pictures of human faces and pictures of scenes.
First they used an advanced type of MRI technology to get a window into the minds of the study's participants.
"We're starting to get to the point where we can pretty reliably sort of read out what a person is thinking about, seeing [and] trying to remember. And we're doing this on a moment-to-moment basis," says Lewis-Peacock. His team's MRI machine learned to recognize the unique pattern that emerges when each participant thinks of faces, scenes or both at the same time.
Then, while participants were loaded in the MRI, they were shown pictures of faces and scenes. They were then repeatedly asked to recall the pictures — in most cases just the images of scenes. "Most of the time, I'll show you both [then] test you on the scene. You can basically forget the face at that point," Lewis-Peacock told them.
The minds of participants were now presumably focusing on the memories of the scenes alone. "But occasionally I'm going to sort of trick you and say 'Aha, no: On this trial I'm actually going to test your memory for the face item,' " which forces your brain to quickly pull the face item back to mind, Lewis-Peacock says.
For many participants this meant suddenly both the scene and the face memories existed in their heads at once — competing with each other.
The research team used their MRI to verify that both memories were present at once, and 30 minutes later they did another test for memory of that scene. Indeed, in the trials where competition had taken place, memory for scenes weakened significantly. The upshot: people had more trouble recalling a memory when it had earlier been simultaneously active with another one.
Jarrod Lewis-Peacock cautions that more testing is required before researchers can strongly recommend certain memory-enhancing techniques. Still, he says one interpretation of this is that "switching between thoughts cleanly or efficiently is a good thing."
"When you're done thinking about something you totally pack it away. Don't let it sit in the back of your head," he says. "Because if you do, it might thrust it accidentally into competition with what you're moving on to think about."
Lewis-Peacock also says this competition theory of forgetting points to the limitations of our own minds.
"I think what this data is suggesting is that there might be these unintended consequences to the way that we're juggling thoughts in our head," he says. "Maybe it's not just a whole big free lunch that you can try to do as many things as you can try to without any repercussions."
WADE GOODWYN, HOST:
There are times when we're all forced to juggle multiple thoughts in our head at once. Maybe you have to pick up milk on the way home and then you realize you also need to send an email for work. And in the end, you forget the milk or the email or both. NPR's Chris Benderev reports that scientists have a new theory that may explain why.
CHRIS BENDEREV, BYLINE: Before we get to that theory, I want you to meet someone whose livelihood depends deeply on not forgetting anything.
GRANT VAUGHT: Hey, folks, good evening. How are you? My name's Grant. I'll be taking care of you this evening.
BENDEREV: Grant Vaught is a waiter at Birch and Barley, which is this swanky restaurant in downtown Washington, D.C. It's so swanky, in fact, that Vaught does not write down orders. He just memorizes them.
VAUGHT: Going to the next table that just got sat now.
BENDEREV: His first order of the night...
VAUGHT: My Blueberry Nightmare, sure.
BENDEREV: Some fancy cocktails.
VAUGHT: The Creme Brulee at full pour, absolutely.
BENDEREV: The trick is Grant Vaught only has to remember the order long enough to get back to his computer...
VAUGHT: She's starting off with the My Blueberry Nightmare on seat one.
BENDEREV: ...Where he can input it and then forget it.
VAUGHT: Seat two's getting a full pour of the Creme Brulee.
BENDEREV: His next table...
VAUGHT: Good evening, folks, how are we?
BENDEREV: They want a couple of beers, French bread, a fig and prosciutto flatbread, brussel sprouts, macaroni and chicken, which is easy. It's all going in the computer.
VAUGHT: So I have the brussel sprouts to start.
BENDEREV: The next table wants a flight of five different beers, which Vaught repeats to himself on the way back to his computer.
VAUGHT: So the Andescher Doppelbock Dunkel, BFMXIV...
BENDEREV: But then a problem - another customer stops him. She knows the chef from way back and she can't remember - she's just dying to know...
VAUGHT: If he has a dog or a cat - that's a good question. Let me find out for you.
BENDEREV: And at this point, I think most of us would try to hold both the beer orders and the pets in our head at the same time.
VAUGHT: So the Andescher Doppelbock Dunkel - a dog or a cat - BFMXIV - a dog or a cat - and a smoked porter - a dog or a cat...
BENDEREV: But that might not be such a smart move because, according to a neuroscientist at UT Austin named Jarrod Lewis-Peacock, you would be allowing your two memories to compete, which can be bad because...
JARROD LEWIS-PEACOCK: When these memories are tightly competing for our attention, the brain steps in and actually modifies those memories.
BENDEREV: The winner of the competition becomeS stronger and the loser, it turns out, can be forgotten.
So there's, like, a battle going on in people's brains in a way.
BENDEREV: Jarrod Lewis-Peacock and others have found this in numerous studies. A recent one in the journal Nature Communications describes an experiment where Jarrod Lewis-Peacock made two memories compete in participants' heads. It wasn't memories of beers or pets; just memories of faces and landscapes. He did this over and over and almost every time he asked people to recall only the landscapes that they'd memorized, so that's all they expected.
LEWIS-PEACOCK: But occasionally I'm going to sort of trick you and say aha, no, on this trial I'm actually going to test your memory for the face item.
BENDEREV: Which is sort of like being asked out of nowhere...
VAUGHT: If he has a dog or a cat - that's a good question.
BENDEREV: The research team used brain scanners to verify that both memories were active at the same time to verify that they were competing. And when they were, one memory did grow weaker. So what does this all mean for your own hectic day? You can still think about multiple things, but maybe, Jarrod Lewis-Peacock says, you should try to avoid thinking about all of them at the same time.
LEWIS-PEACOCK: When you're done thinking about something, you totally pack it away. Don't let it sit in the back of your head because if you do, you might thrust it accidentally into competition with what you're moving on to think about.
BENDEREV: Which brings us back to our waiter Grant Vaught. He went straight to the kitchen to find the chef and ask him about his pets.
VAUGHT: Your friend wants to know if you have a dog or a cat. I don't know why.
BENDEREV: Turns out he has neither, but what about that order for a flight of five esoteric craft beers?
VAUGHT: All right, a little flight here for us.
BENDEREV: Delivered perfectly, of course. Now, if you ask him - and I did later - Grant Vaught isn't exactly sure how he remembered the pets question and the beer or how he remembers most everything that's thrown at him every night. But it could be that he deals with all the orders, all the interruptions and all the favors asked one at a time. Chris Benderev, NPR News. Transcript provided by NPR, Copyright NPR.