Taste as a factor in the management of nutrition.

The sense of taste lies at the interface between the external and internal milieux, at the point at which the animal must decide which chemicals from the environment to incorporate into itself. Accordingly, taste is organized along a neural dimension of nutrients versus toxins, which corresponds to a behavioral dimension of acceptance versus rejection, and to a hedonic dimension of appetitive versus aversive qualities. Reflexive responses, cognitive analyses, and hedonic reactions appear to be managed at different levels of the nervous system. At the first central relay, the nucleus of the solitary tract, somatic reflexes for acceptance or rejection, and autonomic reflexes anticipating digestion are orchestrated. At the second, the parabrachial nucleus of the rodent, associative mechanisms important to the development of conditioned aversions and sodium appetite are manifested. In the thalamic taste relay, gustatory memories associated with non-visceral events may be formed. Primary taste cortex appears to be the site for a cognitive evaluation of gustatory quality and intensity. Finally, a hedonic assessment of the chemical may be made in secondary taste cortex and in the ventral forebrain sites to which it projects. With this assessment comes integration of the gustatory signal with those from other senses, perhaps to create a perception of flavor. Therefore, a sequence that begins with an analysis of the molecular structure of a chemical in the mouth serves to incorporate that gustatory component into an appreciation of flavor, and to participate in the control of motivational processes that guide dietary selection.