In everyday life, people often search their memory for specific information: “Where did I leave the car keys?” “Did I really turn the oven off?” Other times they actively reminisce about the past: “Remember that crazy night out last week?” Not all recall is a choice, however; some forms of memory are involuntary. Perhaps the most famous example is a scene from French novelist Marcel Proust's In Search of Lost Time (also called Remembrance of Things Past). As the narrator drinks some tea and eats a small, plump sponge cake known as a madeleine, the taste brings up a memory of eating the same treat at his aunt's house when he was young.

Researchers are beginning to study a related form of memory called mind pops, fragments of knowledge, such as words, images or melodies, that drop suddenly and unexpectedly into consciousness. Unlike the Proustian example, mind pops, a term coined by University of California, San Diego, emeritus professor George Mandler, seem completely irrelevant to the moments in time and thought into which they intrude. They are more often words or phrases than images or sounds, and they usually happen when someone is in the middle of a habitual activity that does not demand much concentration. (For example: you are doing the dishes when the word “orangutan” springs into your mind for no obvious reason.) Most notably, identifying a trigger for a mind pop in the surrounding environment or even in previous thoughts is extremely difficult—they seem to come out of nowhere.

Psychologists are discovering that mind pops are not truly random—they are linked to our experiences and knowledge of the world, albeit with hidden threads. Research on mind pops is preliminary, but so far studies suggest that the phenomenon is genuine and common. Some people notice their mind pops much more often than others, and frequent mind popping could quicken problem solving and boost creativity. Yet in some people's minds—such as those with schizophrenia—mind pops might evolve from benign phenomena into unsettling hallucinations.

Lia Kvavilashvili, a psychologist at the University of Hertfordshire in England, and Mandler propose that mind pops are often explained by a kind of long-term priming. Priming describes one way that memory behaves: every new piece of information changes how the mind later responds to related information. “Most of the information we encounter on a daily basis activates certain representations in the mind,” Kvavilashvili explains. “If you go past a fish-and-chips shop, not only the concept of fish may get activated but lots of things related to fish, and they may stay activated for a certain amount of time—for hours or even days. Later on, other things in the environment may trigger these already active concepts, which have the feeling of coming out of nowhere.” This phenomenon can boost creativity because, she says, “if many different concepts remain activated in your mind, you can make connections more efficiently than if activation disappears right away.”

Recently Kvavilashvili and her colleagues published a study looking at a possible dark side of mind pops. The researchers wondered just how similar everyday involuntary recall is to intrusive thoughts and hallucinations observed in mental disorders such as depression, post-traumatic stress disorder and obsessive-compulsive disorder. The results, which appear in an April issue of Psychiatry Research, suggest that mind pops are more common among the mentally ill than among the healthy, but it is far too soon to definitely link the sudden memories to hallucinations.

Kvavilashvili has been working on more studies about the phenomenon, in particular one on musical mind pops and their relation to songs that continually replay in people's heads. “The study of mind popping is still in its infancy,” she notes. “I got curious about them because they seemed so random, but these mind pops are genuine fragments of knowledge about the world. What it shows us is that our subconscious often knows the meaning of an experience, even if consciously we don't.”