Taste is a vital sensory process that facilitates the ingestion of nutritive substances and the avoidance of toxins. It is not surprising, then, that the perception of taste stimuli is highly informed by the homeostatic state of the organism (Jacobs et al., 1988; Morton et al., 2006) as well as prior experiences with appetitive and aversive stimuli (Chang and Scott, 1984; McCaughey et al., 1997). Physiological processing of taste stimuli begins with transduction at the level of taste receptor cells distributed throughout the oropharyngeal cavity and extends across a network of central neural structures. The sensory domain of the taste system can be divided into a finite number of qualities or modalities, defined as a group of chemicals that produce similar taste sensations and which are psychophysically independent of other taste qualities. Historically, psychophysicists defined four basic taste qualities: sweet, sour, bitter, and salty. Recently, however, the designation of a fifth quality, umami (savory), has been supported by genetic and physiological data from peripheral taste cells (e.g., Zhao et al., 2003). The designation of discrete taste modalities rests on physiological evidence from every level of the nervous system and bears important functional implications for the homeostatic and hedonic mediation of nutrient intake and toxin avoidance.