If you’ve ever walked into a room and couldn’t remember why you went there in the first place, or had trouble recalling a name or word you just said, this story is for you. Scientists previously thought forgetting things like that meant these thoughts left your short-term working memory, but a now a study says your brain is just at rest, in a sleeping, latent state, until it’s reactivated.
“Earlier experiments showed 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. By incorporating new testing, Dr. Postle and his team have revealed just where the neural trace of that word is held until it can be cued up again.
This research serves as an amendment on how scientists previously thought memory worked. Psychologists believed that short-term memory disappeared the moment you stopped thinking of something, and that long-term memory permanently rewired neural connection. This study adds the idea that behind-the-scenes thoughts are warehoused in the brain and represent a third type of memory. It also introduces the concept that short-term working memory isn’t stored in one place, but rather is spread throughout the brain depending on what someone is recalling.
“Although there is a lot of activity in the prefrontal cortex, there is little evidence that this activation corresponds to the short-term storage of information,” said Postle. “We are taught that this is the way that short-term memory works, that information is shuttled into the prefrontal cortex and it stays in an active mode until it is shuttled into long-term memory storage in the hippocampus. Our work suggests a different scenario.”
How The Study Worked
While study participants were shown two items from a set of three (a face, a word and a pattern of dot motion) on a computer screen, scientists used an encephalogram (EEG) to record their brain activity. First they were asked to remember both items; then, after the items disappeared from the computer screen, a cue indicated which of the two would be the first to be tested.
Researchers were able to uncover what happens when the second uncued item was waiting in working memory. With the subject’s attention focused on the first item, scientists thought there would be a weaker signal for the uncued item in the EEG, but instead the signal vanished completely. However, participants could still recall it later, which means the uncued item remained “silently” in the working memory and was not represented by continuous neural activity.
Postle believes this data proves that working memory resides in patterns of connectivity between neurons and may not require sustained, elevated brain activity.
“Our findings have important implications for understanding working memory,” said Nathan S. Rose, PhD, assistant professor of Psychology at the University of Notre Dame in Indiana, the first author on the Science paper. Rose carried out the work when he was at the University of Wisconsin-Madison. “Our findings introduce a potential avenue for reactivating and strengthening representations that underlie many classes of high-level cognition.”