What you just thought may be ‘sleeping’

If you’ve ever forgotten why you just entered a room, you know how fickle memory can be. One moment it’s obvious why you walked down the hall, and the next moment you’re standing there befuddled.

Here today, gone in a millisecond. At least that’s how we used to think about short-term, or working, memory. But a study just published in the journal Science tells a different story. A recent idea or word that you’re trying to recall has not, in fact, gone AWOL, as we previously thought. According to new brain-decoding techniques, it’s just sleeping.

“Earlier experiments show that a neural representation of a word disappeared,” said the study’s lead author, Brad Postle, a professor of psychology and psychiatry at the University of Wisconsin-Madison. But by using a trio of cutting-edge techniques, Dr. Postle and his team have revealed just where the neural trace of that word is held until it can be cued up again.

Their study amends the long-standing view of how memory works. Until now, psychologists thought that short-term memory evaporates when you stop thinking about something, while long-term memory permanently rewires neural connections. The new research reveals a neural signature for a third type of memory: behind-the-scenes thoughts that are warehoused in the brain.

In the study’s four experiments, a total of 65 students viewed a pair of images—some combination of a word, a face or a cloud of moving dots—on a screen. During a 10-second period, the students were prompted to think about one of the two images they had seen. After a brief delay, they had to confirm whether a picture they saw matched one of the first two images.

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