You see a woman on the street who looks familiar — but you can't remember how you know her. Your brain cannot attach any previous experiences to this person. Hours later, you suddenly recall the party at a friend's house where you met her, and you realize who she is.
In a new study in mice, researchers have discovered the place in the brain that is responsible for both types of familiarity — vague (模糊的) recognition and complete recollection. Both, moreover, are represented by two distinct neural (神经系统的) codes.
The brain's signature for strangers turns out to be simpler than the one used for old friends — which makes sense, says study co-author Steven Siegelbaum, given the vastly different memory requirements for the two relationships. "Where you were, what you were doing, when you were doing it, who else was there — the memory of a familiar individual is a much richer memory," Siegelbaum says. "If you're meeting a stranger, there's nothing to recollect."
The action occurs in a small sliver (小块) of a brain region called the hippocampus, known for its importance in forming memories. The sliver in question, known as CA2, seems to specialize in a certain kind of memory used to recall relationships. "The new work really emphasizes the importance of this brain area to social processing, at least in mice," says Serena Dudek, a neuroscientist at the National Institute of Environmental Health Sciences, who was not involved in the study.
CA2 is unlikely to act alone in this process because it connects to other brain regions that also play roles in social learning, memory and behavior, Dudek says. But if the findings in mice apply to humans, the work could help researchers uncover the roots of social difficulties in people.
From there, researchers might find ways to improve social memory. "How many different disorders of memory are there?" Siegelbaum says. "Do they all involve the same type of changes in neural processing, or are there more specific changes that are associated with different forms of disease?" Having a better way to classify these changes may lead to more targeted treatments, he adds.
