How doe a mammal know what a smell is, and more importantly, how does a mammal learn new smells?

Recent research suggests that different kinds of neurons reorganize in novel ways in response to olfactory signals to produce an olfactory memory.

Below is a video made by the research team that explains this. If that video does not render correctly for you, click here to see it on the original page.

From the press release:

The human brain has the ability to recognise and process a very wide range of sensory stimuli, from which it builds a mental representation. But do these representations change over time? Can we learn to classify and interpret stimuli more e ectively? Neuroscientists at the University of Geneva (UNIGE) have been trying to answer these questions by studying the olfactory system of mammals. They have succeeded in identifying the complementary role played by two dis- tinct kinds of neurons in processing olfactory information and the different brain reorganisation that occurs depending on the context. After having previously demonstrated the possibility to boost the capacity to distinguish similar smells by regulating the inhibition of certain neural networks, the scientists now explain why the brain has to make use of di erent sorts of cells to form, maintain and res- hape the representations of odours. In fact, it is their very combination that enables us to recognise and distinguish similar smells. Find out more about the research outcomes in the journal Neuron.

I have not read the paper, but this looks seriously interesting. It addresses, among other things, the question of how much olfactory sense (sens-ability?) is built in (genetic) vs. learned, and how that learning happens.