Smell Perception Uses Combinatorial Coding

This animated video demonstrates current thinking about combinatorial coding in the nose. Odors are represented by different shaped objects floating in the air. Odors interact with olfactory sensory neurons that express different odorant receptors that are color-coded in the animation. Note that the blue odorant activates only three of the four different types of olfactory sensory neurons. Interestingly, different neurons respond differently to the same odor, showing strong, medium, and weak activation. Action potentials that result after odorant receptor activation propagate down the axon of each olfactory neuron and lead to differential activation of olfactory glomeruli in the olfactory bulb. Inhibitory interneurons will modulate this signal and transmit a filtered signal to higher brain centers.

Three-dimensional animation by Joe Alexander, Information Technology, The Rockefeller University, 2006.