Learning from spiny lobsters about chemosensory coding of mixtures

Studies of the peripheral olfactory system of the Caribbean spiny lobster Panulirus argus and related decapod crustaceans have helped us understand mechanisms of coding of mixtures, some of which are discussed in this review. Although the number of cells in the lobster's olfactory system is much lower than in vertebrate olfactory systems, it is a highly complex system. The receptor neurons (RNs) of this olfactory system are complex processors that cannot be categorized into discrete cell types, but rather have a diversity of response profiles. Each RN can have different types of receptor proteins, second messengers, and/or ion channels, which undoubtedly contributes to the functional diversity of these neurons and makes them complex peripheral integrators. The RNs probably encode information about the quality of mixtures as a distributed or population code, providing a basis for behavioral discrimination of natural food stimuli. Analysis of distributed codes for a series of blend ratios of binary mixtures reveals that the qualities of individual compounds are probably not lost when mixed. Such peripheral processing allows spiny lobsters to perceive complex odors as a set of elemental cues if the salience of the components is sufficiently high.