2013 Sensory Physiology

individual primary afferent neurons express a single type of receptor

each neuron that expresses a particular receptor type projects to a specific glomerulus within the main olfactory bulb (MOB), establishing an organizational map at the level of the second order neurons

• i.e., dark and light green ORNs are scattered randomly throughout the main olfactory epithelium, but their axons segregate into different glomeruli

this indicates that olfactory information processing has some characteristics of labelled line theory

this segregation sets up a mechanism whereby odourants can be coded by the pattern of activity in the olfactory bulb

odourants can be coded based on the combination of receptors that respond (14 are shown here)

Richard Axel and Linda Buck won the 2004 Nobel prize in Medicine for unraveling the coding scheme for odourants

systematic mapping of the responses to >300 odourants (reviewed in Johnson and Leon, 2007) confirms the spatial organization of the olfactory bulb: an odourtopic map that has a similar organization to the stimulus-specific maps found in other sensory systems

these studies have also shown that lateral inhibition narrows the range of chemicals that indivdual olfactory bulb neurons respond to