The brain's long-term memory allows us to hold onto experiences long after we initially encountered them. But short-term memory is a more fleeting and mysterious phenomenon, allowing us to hang onto a thought only until we're distracted by something else.
While the basics of how the brain creates long-term memories is decently well understood - it's basically just a question of encoding data in the brain so that it can be recalled later - short-term memory is harder to understand. After all, the whole point of short-term memory is that nothing is being recorded, at least not for more than about twenty to thirty seconds. Researchers at the Max Planck Institute for Biological Cybernetics - which is one of the more awesome things a Max Planck Institute can be for - decided to get to the bottom of this mystery.
Previous research has shown that structures in the frontal region of the brain are involved in short-term memory, whereas visual information is processed in areas found in the back of the brain. That's tricky, because the subjects of short-term memories are often things you just saw - in other words, visual information. Those two distant parts of the brain need to be able to work together for our brains to hold onto visual information in the short-term.
To figure out how all this works, the researchers showed some images to monkeys while recording electrical activity in both of these key regions of their brains. After being initially shown one picture, the monkeys would be shown another after a short break, and they had to use their short-term memory to figure out whether they were looking at the same picture or a different one.
Here's where things get interesting - the electrical activity revealed strong oscillations in a particular set of frequencies known as the theta-band. What's more, the frequencies coming from the two separate regions of the brain actually synchronized together when the monkeys tried to recall information from their short-term memory. The level of synchronization varied, but the more lined up the two sets of frequencies were, the better the monkeys were at remembering what they had seen. In a statement, first author Stefanie Liebe describes this phenomenon:
"It is as if you have two revolving doors in each of the two areas. During working memory, they get in sync, thereby allowing information to pass through them much more efficiently than if they were out of sync."
It's a really intriguing result, as it helps show how distant regions of the brain can communicate to perform complex acts at breakneck speed. It's pretty amazing to think of a pair of electrical currents whose frequencies are constantly spinning in and out of sync in our brains every time we try to remember something we were looking at five seconds ago.