To study the sense of smell is to sign on for a challenge. The olfactory bulbs comprise an elaborate network of cell types and connections, and olfaction begins with input from odor receptors expressed by sensory neurons in the nose: about 400 different receptor types in humans, 1,000 in mice. Each receptor can typically respond to several different odorants. Compared to the visual system, which has just three color receptors—for red, green, and blue—olfaction is complex.
Furthermore, the stimuli themselves are complex. A seemingly simple aroma like fresh strawberry may comprise multiple odorants, each activating different receptors. And should you waft the enticing scent under the nose of a mouse, how do you control precisely when it inhales those odor molecules, and when the neural receptors are activated? “It’s a notorious problem to control stimulus for the olfactory system,” says Rainer Friedrich, a professor at the Friedrich Miescher Institute for ...
