“Smell is having a moment”

Reading: The biology of smell is a mystery — AI is helping to solve it, Nature, 3 Sept 2024.

For light, the human eye has two types of receptor cell; for smell, there are 400. How the signals from these receptors combine to trigger a particular perception is unclear. Plus, the receptor proteins themselves are hard to work with, so what they look like and how they function has mostly been guesswork.

And the best guesses today:

The nose has millions of olfactory neurons, and each typically expresses just one type of odorant receptor (OR). […] Each of these receptor types might recognize one or more odorants — and each odorant might be recognized by more than one receptor. Together, the roughly 400 human ORs can respond to a trillion different chemicals.

Related to this, the Odor2Action group is interesting. They are trying to answer the question of how animal brains translate odour infomation to changes in their behaviors.

I’ve been to a couple of talks on the hardware you need to do any kind of smell work. It’s way beyond anything I understand:

Uploaded image — Slide from a talk at the University of Sussex A-Life seminar sometime this century.

Addition, 9 October 2024: olfactory cortex cells “recognize not only odors, such as bananas and black licorice—but also images and words associated with those smells, according to single-neuron recordings from 17 people.”