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In French author Marcel Proust’s 1906 novel À la recherche du temps perdu (In Search of Lost Time), a bite of madeleine cake triggers a flood of childhood memories. Scientists call this phenomenon “Proust’s madeleine,” and it was even featured on The Sopranos. Now a study in PLOS Biology suggests these vivid memories of early childhood smells are encoded in very specific parts of the brain.

“Smells are exceptional cues for accessing autobiographical memories,” says the study’s co-senior author Nathalie Mandairon of the Lyon Neuroscience Research Center in France. Scientists suspected for decades that the phenomenon involved certain brain areas, specifically long-lived “granule” cells in the brain’s olfactory bulb, or smell center. These relatively tiny cells are created on the very first day of a child’s life and are primed to capture pleasurable smells from their first decade—which may explain why childhood memories evoked by smells can be so vivid even when they were thought to be forgotten.

Mandairon’s team surveyed more than 600 volunteers and found that most had remembered pleasant childhood experiences from the “Proust’s madeleine” phenomenon. The researchers then exposed mice to pleasing natural scents when they were about three to four weeks old, an age that roughly corresponds to early childhood in humans. Normal mice were drawn to the scents—but not mice whose granule cells had been silenced by optical fibers that the researchers implanted in the animals’ brains to switch these cells on and off.

The reaction confirmed that early smells are imprinted in the granule cells of the brain’s olfactory bulb, perhaps because these cells can make “privileged connections” with the brain areas for pleasure and reward, the study says. The human responses suggested that mainly positive memories are linked to the phenomenon.

Physical chemist Hervé This, director of France’s AgroParisTech-INRAE International Center for Molecular and Physical Gastronomy, says the study gives a “fascinating” explanation of the brain areas involved. But he would have liked to see it account for negative childhood memories as well because “unpleasantness is equally significant.” He adds that he has experienced the phenomenon himself: pâté lorrain has to be cooked for exactly one hour to match the taste from his childhood.

Another expert, however, broadly welcomes the study but thinks that the singular role of smell in memory may only be an illusion: Every sense has the power to evoke strong memories, says biophysicist Luca Turin of England’s University of Buckingham. “The only peculiarity of smell [is] that it is like a password and needs to be exact,” he adds.

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