Memories of childhood scents associated with joy are encoded by neurons generated shortly after birth

A new study published in PLOS Biology reveals that neurons generated shortly after birth in the brain's olfactory bulb granule-cell layer are responsible for encoding childhood memories of scents associated with joy. Researchers surveyed 647 human participants about significant childhood odors, finding that positive emotions like happiness and pleasantness were most strongly associated with these memories, which often originated in early life and evoked vivid, emotionally powerful recollections.

In a mouse model, juvenile mice exposed to an attractive odor in an enriched, playful environment showed a preference for that scent in adulthood compared to mice exposed to the same odor in normal housing. This memory preference relied on increased functional connectivity in the brain's reward system, and specific neurons born during the first day of life in the olfactory bulb granule-cell layer were found to be particularly activated by the odor associated with positive emotions.

Silencing these neurons using optogenetics reduced the preference for the odor, indicating their crucial role in the early recall of childhood smell memories. However, by 6 months of age, the memory faded unless periodically re-exposed to the scent, suggesting that long-lasting odor memories may rely on reorganization of the brain's functional networks, shifting from the reward system to the olfactory-limbic system.