One nostril knows what the other learns: Olfactory plasticity

About 30% of the adult human population does not perceive an odour when sniffing the steroid androstenone (5-α-androst-16-en-3-one), but will become sensitive to its smell after repeated exposure to the compound 1 , 2 , 3 . Here we investigate the origin of the plasticity that governs this acquired ability by repeatedly exposing one nostril of non-detecting subjects to androstenone and then testing the unexposed nostril. We find that the exposed nostril and the naive nostril can both learn to recognize the smell, effectively doubling detection accuracy. As the two olfactory epithelia are not connected at the peripheral level, our results indicate that learning occurs in the brain by a mechanism that shares information from both nostrils.