The Role of the Parabrachial Nucleus in TasteProcessing and Feeding

摘要

The parabrachial nucleus (PBN) was identified as a taste relay in rodents in 1971. Earlyrecordings suggested that the PBN transmitted a faithful representation of taste ac-tivity from the nucleus of the solitary tract (NTS). However, its role assumed greatersignificance as its subnuclei were shown to deal with different aspects of taste, visceralsensations, hedonics, and conditioned aversions. The discovery of parallel projectionsfrom PBN to the thalamus and to ventral forebrain, and evidence that the former carried -sensory information while the latter signaled hedonics, conferred on PBN a central rolein guiding feeding. Thus, it was surprising to discover that the PBN is not a taste relay inprimates. So arose a distinction between rodents, in which parallel processing of tasteand hedonic information is the rule, and primates, where serial processing through thecortex precedes a hedonic assessment. Where does the integration of taste and hedonicsoccur, and how does this affect feeding? Neurons in both NTS and PBN of rodents aremodified by changing physiological conditions. That altered activity parallels and per-haps directs the rodent's feeding behavior. Information from primate NTS implies nosuch modification. These interactions are reserved for orbitofrontal cortex and ventralforebrain. The implication is that in rodents, hindbrain alterations not only control thereflexes associated with taste, but also direct food selection through the PBN—ventralforebrain projections. In primates, the apparatus is in place for an independent cog-nitive analysis unaltered by physiological state, upon which a hedonic assessment issubsequently overlaid.