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Scientists at the Stowers Institute for Medical Research have a new hypothesis about how the brain processes odors. While they had previously believed in a chemotopic model in which different types of fragrances, such as amines and ketones, were received by clusters of cells next to each other, they found that when different molecules traveled into the brain, their pattern was more random.
This led them to develop a tunotopic model. In this model, glomeruli (receptors on the brain's olfactory bulb) are not designed to differentiate chemical structures of molecules, but rather are tuned to specific smells. They are grouped near other glomeruli with similar tuning capabilities and are able to acquire mutations to register new smells. Essentially, they can work together to distinguish similar smells and identify nuance, and they can also adapt to any of the hundreds of thousands of odors we come across.
C. Ron Yu, who led the study, says that this hypothesis may have implications for visual, auditory and somatosensory processing too.