1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

305 Symposium Approaching Taste and Olfaction at theSystems LevelTHE INTEGRATION OF MULTIPLE SENSORY MODALITIESAND THE CREATION OF FLAVORBreslin P.A. 1 1 Monell Chemical Senses Center, Philadelphia, PAThe central neural creation of flavor from stimulation originatingwithin the upper airways represents what is arguably the single mostprofoundly multi-modal sensory integration of which the brain iscapable. Inputs from the upper airways reflect taste (salt, sweet, bitter,sour and savory), olfaction (and it myriad qualities), static tactilesensations (touch, pressure, stretch), dynamic tactile sensations(vibration, astringency, creaminess, viscocity, coating), thermalsensations (warm, cool, hot, cold), nociception (stinging, burning,prickling, itching), proprioception (bolus texture, resistance, chewiness,brittleness, crunchiness), and auditory input (via the sounds arising inthe oral cavity and bone conduction when foods are manipulated andchewed). Flavor may be conceived of or defined as the congruentintegration of all these inputs into a single perceptual gestalt that isprojected to originate within the mouth. Some of these differentphysical inputs may interact at the receptor cell or primary afferent levelsuch as thermal-taste or tactile-taste interactions. Higher in the CNSthere are brain areas that appear to process and relay inputs from all ofthese modalities such as the insula/operculum, orbitofrontal cortex, andamygdala. How these diverse systems are integrated, under whatconditions, and the role of attention and learning in these pathways arethe focus of an ever-growing and fascinating body of research.306 Symposium Approaching Taste and Olfaction at theSystems LevelLEARNING TO SMELL: CORTICAL PLASTICITY AND ODORPERCEPTIONWilson D.A. 1 1 Zoology, University of Oklahoma, Norman, OKOlfactory perception involves at least two distinct processes. First,most odors are composed of several to hundreds of volatile molecules.However, under most conditions odor perception is synthetic, withlimited access to the underlying features of complex mixtures. Thus,multi-component odorant mixtures can be perceived as unique odorobjects through experience-dependent mechanisms hypothesized to besimilar to object perception in vision. Second, odors are almostinvariably experienced against odorous backgrounds from which theforeground odor must be extracted from the background through ananalytical (as opposed to synthetic) process (figure-ground separation).Work in our lab has been examining piriform cortical contributions toboth of these processes. Here I will focus on the process of olfactoryfigure-ground separation. Neurons within the piriform cortex showrapid, odor-specific adaptation, despite relatively maintained input fromolfactory bulb mitral/tufted cells. This cortical adaptation is mediated bypre-synaptic metabotropic glutamate receptors that induce an activitydependentdepression of afferent synapses. Pharmacologicalmanipulations show that cortical adaptation contributes to backgroundodor adaptation and short-term behavioral odor habituation.Behaviorally, rats are able to filter background odors and identify atarget odor presented against that background. Similarly, piriformcortical neurons adapt to background odors, and respond to novel targetodors presented against that background as if the target odors werepresented alone. These findings present a specific cortical mechanism toallow perception of odors in odorous backgrounds. Supported by NIH& NSF.307 Symposium Approaching Taste and Olfaction at theSystems LevelNEURAL POPULATION CODING OF SATIETY STATESDe Araujo I. 1 1 Neurobiology, Duke University, Durham, NCVoluntary feeding involves behavioral states associated with mealinitiation (hunger) and termination (satiety). In this activity multiplebrain regions act in concert to regulate the onset of these behaviors.Previous electrophysiological investigations revealed that singleneurons located in primate brain areas such as lateral hypothalamus(LH) and orbital frontal cortex (OFC) decrease their firing rate levels asanimals transition from hunger to satiety. Similar responses wereobserved in human functional neuroimaging studies. We will presentrecent data obtained from hungry rats that have bundles ofmicroelctrodes implanted in their LH, OFC , insular cortex (IC) andamygdala (AM) that freely lick to satiety. These data show that singleunits mostly encode for specific hunger states within a feeding cycle(hunger–satiety-hunger), while neuronal population activity reflects theoverall motivational (hunger/satiety) state across several cycles bycombining information from its constituent units. This population codeseems to be distributed across LH-IC-OFC-AM circuits of both lean andobese/diabetic rats. We suggest that this distributed code underlies thecontrol of voluntary feeding behavior under different metabolic states.This work was supported by grants DC-01065 and Philip Morris USAand Philip Morris International.308 Symposium Approaching Taste and Olfaction at theSystems LevelHEDONIC ASPECTS OF CHEMICAL STIMULI:CORTICOLIMBIC CIRCUITS THAT MEDIATE REWARDAND CHOICE.Balleine B. 1 1 Psychology, University of California, Los Angeles, LosAngeles, CAThat chemical stimuli can exert powerful effects on behavior is dueboth to evolutionary pressures and to learning; i.e. the formation ofassociations with biologically potent events such as nutrients, fluids,illness and so on. Associations of this kind modify the affective valenceand, hence, the preference for specific flavors and tastes but they arealso the basis for changes in the hedonic response to these stimuli.Current evidence suggests that this latter aspect is a product ofcontiguous emotion feedback elicited by the stimulus through a systemof sensory-motivational and affective connections, and that itdetermines the assignment of reward value to a particular stimulus.Thus, for example, shifts in motivational state do not reduce the rewardvalue that animals´ assign to taste stimuli until the effect of the shift instate is experienced through direct consummatory contact with the taste.Sensory-specific satiety is a particularly potent means of producingselective changes in the reward value of stimulus events as indexed bychanges in the performance of actions that gain access to those events.Evidence from rodents will be presented suggested that these changesare mediated by a corticolimbic circuits involving particularlyconnections between gustatory insular cortex, basolateral amygdala andthe nucleus accumbens.77