Postnatal refinement of functional odor maps on the surface of the mouse olfactory bulb

Newborn mice rely on olfactory information for survival, but the nature of odor representation in the neonatal olfactory bulb is not well understood. I compared the spatial pattern of odor-evoked responses in 1 to 11 week old mice by imaging the dorsal surface of olfactory bulbs. By using a large panel (~100) of chemically diverse odorants I was able to assign functional tags to individual glomeruli and identify them reliably across different animals. The relative positions of functionally unique glomeruli were equally precise at all ages examined (1 week to adulthood), arguing for a uniform expansion of glomerular territory over development. Several features of odor maps in pups were different from those in adults. First, fewer glomeruli were activated by odors in 1 to 3 week-old mice than in adults. Second, duplicate glomeruli with the same functional signatures were found in pups almost twice as frequently as in adults. Third, less than 40% of pup glomeruli were functionally similar to adult glomeruli – this proportion increased between 6 and 30 days after birth. Finally, fewer pup glomeruli could be reliably identified across multiple