THE ESSENTIAL
- Research has shown that on average we are able to hold up to four different items in our working memory.
- Earl K. Miller’s lab is planning new experiments to determine if their computer models appropriately match neural data from real brains.
- In these next experiments, rather than a single image, the animals will have to keep several things in mind.
Between the moment you read the Wi-Fi password on a coffee table and the moment you return to your laptop to enter it, you have to keep it in mind for a short time. If you’ve ever wondered how your brain does this, it’s thanks to something called working memory, which researchers have been struggling to explain for decades.
This Tuesday, December 27, neuroscientists at the Picower Institute for Learning and Memory, one of three neuroscience study groups at MIT (Massachusetts Institute of Technology), have published a summary of their research in the journal PLOS Computational Biology. This work provides a better understanding of the functioning of working memory.
2 competing theories to explain working memory
The researchers first took measurements of brain cell activity in an animal performing a task that activated its working memory. An image appeared in front of him, before disappearing and then reappearing a second later accompanied by a new image. He had to watch the original to win a small reward. The key moment is this intermediate second, called “delay period”, during which the image must be kept in mind, which activates the working memory. At that time, neural activity increases a lot when the brain sees the image the first time, then increases again during the memory test.
The neuroscientists then compared these measurements with computer models of neural networks representing the two major theories that explain the mechanism of memorizing short-term information. The results strongly favored the more recent theory that a network of neurons stores information by making short-lived changes in their synapses (the contact region between two neurons where information exchanges). This contradicts the other, older, major competing theory that memory is maintained by neurons remaining persistently active (like an idling engine).
“Working memory is as complex and dynamic as our thoughts”
While both models allowed information to be kept in mind, only versions that allowed synapses to transiently change connections (a process called “short-term synaptic plasticity”) produced patterns of neural activity that mimicked what was actually observed in real brains when working memory was activated.
The idea that brain cells retain their memories by always being “alive” is perhaps simpler, acknowledged in a communiqué the study’s lead author, Earl K. Miller, but it doesn’t represent what nature does and can’t produce the same sophisticated flexibility of the brain when exercising short-term memory. “If working memory were just sustained activity, it would be as simple as a light switch. But working memory is as complex and dynamic as our thoughts”he points out.