Human World

Memories emerge from corners of the mind to do battle

Stanford researchers mapping brain function in real time have found that visual memories can compete with each other, especially if words get in the way. They’ve published their memory competition findings in the March 21, 2011, issue of the Proceedings of the National Academy of Sciences (PNAS).

The first author on the study, Brice Kuhl (now at Yale), and colleagues tracked brain function using an imaging technique called functional magnetic resonance imaging (fMRI). As the imaging part tells you, they could effectively create images of brain function as people were busy thinking about pictures and words. The pictures were either faces or places. With each picture, the study participants saw an unrelated noun above the image and text below it telling them what the picture was. We’ve provided you an example of our own below, using Charles Darwin and the Matterhorn.

While the volunteers looked at the pictures, the researchers got images of their brain activity using the fMRI technology. We process different kinds of visuals along different brain pathways. The scientists could tell by the image type alone if a participant was looking at a face (Darwin) or at a place (the Matterhorn). First, they showed everyone the first round of combined images and nouns. Then, the volunteers had a quick test to see how well they could associate an image and its noun.

After the test, the participants had another round of images with nouns to view. Some nouns showed up again. If they’d been linked with a face in the first round, they were linked to a place in the second round, and vice versa, as we’ve done with “blanket” and the Matterhorn below. The volunteers also got to see a few new noun-image pairings. During all of this viewing, researchers recorded the information about which parts of the brain were active.

Then came the second test session. This time, there were the new nouns and the recycled nouns. Regardless of whether the noun was old or new, the volunteers had to try to recall the last image associated with it.

And that’s where memories started battling it out. Remember that some nouns showed up twice: once with a face (blanket + Darwin) and then with a place (blanket + Matterhorn). The scientists could tell from the fMRI results that with these two choices linked in memory with a recycled noun, the brain areas showed a bit of confusion. Some face-related areas lit up, but so did some place-related areas. The visual memories of each seemed to be competing with each other. Even when a participant remembered which image came second with the recycled noun (the Matterhorn!), the fMRI showed this overlap and confusion.

What does that mean for us? It may mean something you’ve long suspected. When we try to remember things, other possibly similar experiences step in and interfere. Our brains engage in a battle of memory to see which one will take center stage as the starring recollection. The outcome can be confusion in our memories of places and faces. Brice Kuhl and the other Stanford researchers publishing in this PNAS study haven’t solved the problem of what to do about memory competition, but they certainly have taken advantage of fMRI to show that it exists.

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March 31, 2011
Human World

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Emily Willingham

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