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.