Zap! Magnet Study Offers Fresh Insights Into How Memory Works

Dec 1, 2016
Originally published on December 1, 2016 11:13 pm

Forget where you just left your car keys? A magnetic pulse might help you remember.

Some dormant memories can be revived by delivering a pulse of magnetic energy to the right brain cells, researchers report Thursday in the journal Science.

The finding is part of a study that suggests the brain's "working memory" system is far less volatile than scientists once thought.

"This changes how we think about the structure of working memory and the processes that support it," says Nathan Rose, a neurocognitive psychologist studying memory at the University of Notre Dame and one of the authors of the research.

Working memory, he explains, is what allows the brain to retain a new piece of information even when our attention is temporarily directed elsewhere.

Say you're at a cocktail party, for example. You meet two people, learn their names, and start a conversation. As you talk, the conversation shifts to just one of those people.

"But you don't want to forget who the other person is, in case the conversation shifts back," Rose says. And, usually, you don't forget, because your brain has been keeping the name in working memory — ready to use at a moment's notice.

Since the 1950s, the dominant theory about working memory has been that it required continuous activity in the brain cells associated with a particular item, like someone's name. If the activity level dropped, the memory was gone forever, scientists figured.

But Rose and a team of researchers weren't so sure. So they did a series of experiments.

In one, people watched a screen while researchers monitored the activity in their brains.

"We presented two items — like a face and a word," Rose says. The participants were told they needed to remember both.

That caused a distinct pattern of activity in two groups of brain cells: one that was keeping track of the face and another that was keeping track of the word.

But then, Rose says, the researchers had people focus on just one of the items they'd seen. And when they did that, the brain activity associated with the other item disappeared.

"It was almost as if the item had been forgotten," Rose says.

But it wasn't forgotten. When prompted, the participants were able to retrieve their memory of the item. And that caused the associated brain cells to start firing again.

Then the researchers provided an even more dramatic demonstration. They used transcranial magnetic stimulation (via an electromagnetic coil held to the forehead) to deliver a pulse of energy to the brain.

"And when we did that, we saw a brief reactivation of the unattended memory item, as if it was brought back into focal attention," Rose says. The technique only worked, though, if people believed they would need to remember the item at some later time.

This ability to revive a thought with a magnetic pulse quickly became known as "the Frankenstein effect" among scientists in the lab, Rose says.

The results offer strong evidence that brain cells don't have to remain active to sustain a working memory, Rose says. But he's concerned that the public will assume magnetic stimulation can help them recover memories.

"Boy, wouldn't that be great?" he says. "But I think we're a ways away from that."

What's closer, though, is a better understanding of how short-term memory works.

The study strongly suggests that working memories can be stored by changing the connections among neurons, says Joel Voss, a brain scientist at Northwestern University who was not involved in the research

"If you imagine that a particular set of connections can represent a memory, then that set of connections could be reconfigured," he says. "And it could stay in that configuration, even if the neurons aren't persistently active."

Scientists believe that's how long-term memories are stored. And if some short-term memories also use this mechanism, it could explain how they can become long-term memories.

"In order for a long-term memory to happen there has to be some physical trace of that memory," he says. And that's exactly what the study seems to have found.

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ARI SHAPIRO, HOST:

Now here's a story for anyone who's forgotten where they just left their car keys. It's possible to revive this sort of memory by zapping the brain with a magnetic pulse. That finding is part of a new study that challenges the traditional view of how the brain keeps short-term memories. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: The study involves a type of memory known as working memory, and it's not just for car keys. Nathan Rose, a psychologist at Notre Dame, explains working memory this way. He says, imagine you're at a cocktail party.

NATHAN ROSE: You have two people that you meet, and you learn the names of both people.

HAMILTON: Then the conversation shifts, and you find yourself focusing on just one of those people.

ROSE: All the while, you don't want to forget who the other person is in case the conversation shifts back.

HAMILTON: If you do manage to remember the other name, it's because you've placed it in working memory. Rose says the question is, how?

ROSE: How does the brain accomplish this task of keeping this information active while you're focused on other ongoing activities?

HAMILTON: For decades, scientists thought the trick required continuous activity in the brain cells associated with a particular memory. If the activity level dropped, the memory was gone forever. But Rose and a team of researchers weren't so sure, so they did a series of experiments.

In one, people were asked to remember two items while researchers monitored the activity in their brains. When the people focused on one of the items, brain activity associated with the other item disappeared.

ROSE: Almost as if the item has been forgotten.

HAMILTON: But it wasn't forgotten, and the researchers showed this in a dramatic way. They delivered a magnetic pulse to the areas of the brain that were supposed to keep track of the item being ignored.

ROSE: And when we did that, we saw a brief reactivation of the unattended memory item as if it was brought back into focal attention.

HAMILTON: The pulse zapped the memory back to life like some creature in a horror film.

ROSE: My buddy, when I first showed it to him - he dubbed it the Frankenstein effect.

HAMILTON: And it wasn't just something the scientists saw on a screen. When people got zapped, it helped them remember the item they'd been ignoring. Rose says the study, which appears in the journal Science, offers strong evidence that brain cells don't have to remain active to sustain a fresh memory. But he's concerned that the public will read too much into the results with magnetic pulses.

ROSE: I imagine that the response that we'll get is that this may be a way to stimulate the brain to recover memories. And, boy, wouldn't that be great? But I think we're a ways away from that.

HAMILTON: Joel Voss, a brain scientist at Northwestern University, says this research is important because we know so little about memory.

JOEL VOSS: Honestly, we're in the Dark Ages (laughter). There are more questions than there are answers.

HAMILTON: Voss says this study does provide some answers about how working memories are stored in the brain.

VOSS: It indicates that holding an item in working memory or short-term memory causes a dynamic reconfiguration of the structural connections between neurons.

HAMILTON: In other words, it's not just neurons firing continuously. There's an underlying change in the way the neurons are wired together. Voss says that means working or short-term memories appear to be a lot like long-term memories, which are also thought to be stored in the connections between neurons. And he says that could explain how a short-term memory like the name of someone you just met becomes a long-term memory.

VOSS: In order for a long-term memory to happen, there has to be some physical trace of that memory.

HAMILTON: Which is exactly what this study appears to have found. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.