It’s estimated that, on average, people have a tip-of-the-tongue moment at least once a week. Perhaps it occurs when you run into an old acquaintance whose name you can’t remember, although you know that it begins with the letter “T.” Or perhaps you struggle to recall the title of a recent movie, even though you can describe the plot in perfect detail. Researchers have located the specific brain areas that are activated during such moments, and even captured images of the mind when we are struggling to find these forgotten words.

This research topic has become surprisingly fruitful. It has allowed scientists to explore many of the most mysterious aspects of the human brain, including the relationship between the conscious and unconscious, the fragmentary nature of memory, and the mechanics of language. Others, meanwhile, are using the frustrating state to learn about the aging process, illuminating the ways in which, over time, the brain becomes less able to access its own storehouse of information.