ROBERT SIEGEL, HOST:
We're going to delve now into the connections in our minds. Think about when you've run into an old friend, say, at a store or a train station. Your brain creates a memory of the experience, and that memory forever links the person you saw with that place. Well, researchers say that they have been able to watch this sort of association being formed in the brain. NPR's Jon Hamilton has the story.
JON HAMILTON, BYLINE: More than a decade ago, scientists discovered that in one area of the brain, there are special neurons that respond only to a particular person, like the actress Jennifer Aniston. Matias Ison of the University of Leicester in the U.K. says more recently scientists realized that some of these neurons could respond to two people but only if those people were connected somehow.
MATIAS ISON: A neuron that was responding to Jennifer Aniston was also responding to pictures of Lisa Kudrow that was, basically, Phoebe in the TV series "Friends."
HAMILTON: The two actresses were often on screen together, so it made sense that the brain would create a link between them. And Ison thought those special neurons in the medial temporal lobe might be that link. To find out, he and a team of researchers did an experiment. It involved 14 epilepsy patients who had electrodes temporarily implanted in their brains to identify the source of their seizures. That allowed Ison's team to monitor individual brain cells in the medial temporal lobe. First the team identified neurons that respond to pictures of a specific person, like Jennifer Aniston. Then, Ison says, they identified different neurons that responded to pictures of a particular place.
ISON: The Eiffel Tower, the Leaning Tower of Pisa, the Hollywood Sign, the White House - pictures that people will recognize easily.
HAMILTON: Ison says the next step was to form a new association between a person and a place.
ISON: We did that by creating these fake images of - let's say of Jennifer Aniston at the Eiffel Tower.
HAMILTON: When people saw these fake images, it was like running into an old friend at the train station. The experience created a new memory linking the person and the place. And Itzhak Fried of the University of California Los Angeles says that caused neurons in the medial temporal lobe to change their behavior. For example, he says, take a neuron that had responded only to Jennifer Aniston.
ITZHAK FRIED: When the association is created, suddenly the cell very rapidly changes its firing properties and now will start responding also to the Eiffel Tower.
HAMILTON: Fried says this sort of change helps explain how the brain creates memories of experiences which may involve not only people in places but emotions and sensations and lots of other information. And he says when we recall an experience, these special neurons may help us reassemble all the relevant information. Fried says the study may also help explain what's going wrong in the medial temporal lobe of people who have trouble forming new memories.
FRIED: We know in situations like Alzheimer, you know, one of the very first changes that you see is in this very area.
HAMILTON: And Fried says if those changes affect the neurons that help make associations, it would explain why people with Alzheimer's can't remember things like where they parked their car.
FRIED: I have to create an association between my car and that particular place, right? The association is not created, then I will not be able to find my car.
HAMILTON: The study also backs the idea that memories can be formed very quickly says Michael Kahana, a professor of psychology at the University of Pennsylvania. He was not involved in the research.
MICHAEL KAHANA: Even a single, brief exposure to any information changes the human brain. And that's something that if you think about it, it must be true. But it's not something that we often recognize.
HAMILTON: Even though science has now shown that just one glimpse of Jennifer Aniston at the Eiffel Tower can change a human brain. The new research appears in the journal Neuron. Jon Hamilton, NPR News.
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