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Tuesday, May 11, 2004

Brain Day, Part 1: Smell 

Today's a big neuroscience day for me, so I'm writing it in bits. Enjoy!!

People generally believe that they don't have as good a sense of smell as other animals. And scientists have long agreed, based on research indicating that we have fewer olfactory receptors than other mammals (350 functional genes versus 1100 for mice). But, in a paper published today, a researcher examines these data, as well as many other items, and concludes that we may be better than we think:

While other mammals have more receptors than we do, they also have bigger noses which contain complex filtration systems, presumably evolved to protect against the dirt and contaminant laden ground they life close to. As primates became more and more bipedal, this was no longer necessary, and so selective pressure no longer maintained this feature. It was more advantageous to have eyes closer together for real stereoscopic vision. Now, with no filtering apparatus blocking a portion of the smell molasses inhaled, we can get by with fewer receptors. In tests, humans performed better at detecting long-chain aldehydes than dogs, but worse at short-chain. Which makes sense: long-chain molecules are more likely to get caught by the dogs' filters, short ones not as much.

Humans also have more developed cognitive abilities to analyze smells: what our receptors get is easier for us to interpret than for dogs.

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