1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

401 Poster Central Taste and Chemosensory BehaviorENSEMBLE RESPONSES OF GUSTATORY CORTICALNEURONS ACCURATELY PREDICT TASTANT IDENTITYJones L.M. 1 , Fontanini A. 1 , Katz D.B. 1 1 Brandeis University, Waltham,MAGustatory neurons respond to tastants with patterns of spikes that arehighly variable—both throughout the time course of a single responseand across repeated deliveries of the same stimulus. Yet currentanalyses of coding in the gustatory system rely heavily on time and trialaveraging. Here we investigate cortical processing of taste stimuli usingHidden Markov Modeling (HMM), an analysis method that does notaverage over time or trial, but instead classifies responses in individualtrials as progressions through different neural states. We recorded extracellularactivity from small ensembles of well isolated neurons (6-12simultaneously) in the gustatory cortex of awake rats while the 4 basictastes were delivered via intra-oral cannulae. We found that theensembles reliably transition through a taste-specific series of states(defined by the firing rates of each neuron). This allowed us to predicttastant identity from single trial responses and compare thesepredictions to those computed using a method based on averaged firingrates. HMM predictions were consistently more accurate than theaverage-based method (10 of 12 sessions). Examination of HMMsolutions revealed the source of their high-quality performance: theexact timing of the progression through a taste-specific set of statesvaried from trial to trial, such that some of the information available insingle trials using HMM was lost in the across-trial averages. Thisindicates that the gustatory cortex may utilize specifically timedchanges in firing patterns of neural ensembles to process tasteinformation. Supported by 1 R01 DC006666 to DBK.403 Poster Central Taste and Chemosensory BehaviorANTICIPATORY CORTICAL ACTIVITY IN A TASTEDISCRIMINATION TASKGutierrez R.M. 1 , Nicolelis M.A. 1 , Simon S.A. 2 1 Neurobiology, DukeUniversity, Durham, NC; 2 Anesthesiology, Duke University, Durham,NCPreviously we have shown that when freely licking rats know whattastant will be delivered, their anticipatory cortical activity candistinguish among them Gutierrez et.al. J Neurophysiol 95:119–133(2006). Here we explore whether such discrimination would be presentwhen the animal does not know which tastant will be delivered. Thiswas accomplished by recording the activity of neuronal ensembles inthe OFC, insula and nucleus accumbens while rats performed a tastediscrimination task. For this task, rats were trained to lick an empty tube(10 times) in order to randomly receive NaCl (positive cue) thatsignaled the availability of a reward (sucrose) or MSG (negative cue)that signaled the delivery of quinine. Importantly, taste cues (NaCl,MSG) and outcomes (sucrose, quinine) were delivered in identical, butindependent compartments and rats initiated licking in a similar way inboth compartments. The anticipatory activity in the “cue” compartmentwas similar, meaning that when rats do not know what tastant will bedelivered, there is not any anticipatory activity related to the identity ofthe tastant. However, in the "outcome" compartment, we founddifferences in the anticipatory activity of the expectation of sucrose orquinine. Of the three cortical areas explored, we found a greaterpercentage of neurons in the nucleus accumbens that increased firingrate in the "outcome" compared to "cue" compartment. In summary adistributed number of cells in the brain anticipate behavioral outcomesonly when the rat knows what reward is coming. Supported by NIHDC-01065 and Philip Morris USA Inc. and Philip Morris International402 Poster Central Taste and Chemosensory BehaviorGUSTATORY CORTEX ENCODES MULTIPLE FEATURESDURING AN INTENSITY DISCRIMINATION TASKMacDonald C.J. 1 , Nicolelis M.A. 2 , Simon S.A. 2 1 Psychological andBrain Sciences, Duke University, Durham, NC; 2 Neurobiology, DukeUniversity, Durham, NCPrevious work on taste intensity processing in gustatory cortex (GC)of awake animals relied on integrated neural activity without taking intoaccount the behavior of the animal. To this end, we used chronic multielectroderecordings in the behaving rat to characterize GC activityduring a NaCl intensity-discrimination task. In this task, the rat lickedon a “sample” lick spout positioned in the center of the chamber walland could receive 20 µL of 30 or 120 mM NaCl (perceptual anchors)during a trial after each of two successive licks. These anchors wererewarded with water after correctly licking on one of two “choice” lickspouts positioned to the left or right of the sample spout, whichcategorizes the concentration as “High” (120 mM) or “Low” (30 mM).Intermediate NaCl concentrations were also delivered during theexperiment but were not rewarded. The probability of categorizingNaCl as “High” increased with NaCl concentration. We identified twosub-populations of neurons whose firing rate monotonically increasedor decreased within one lick in response to concentration. We alsoidentified several additional neuron “types” including licking and watersensitive neurons in addition to neurons that changed activity at definedpoints during the behavioral sequence that makes up a single trial. Insummary, these data show that the GC contains many different neuronaltypes that mediate different aspects of taste-guided behavior. This studywas supported by grants DC-01065 and Philip Morris USA and PhilipMorris International.404 Poster Central Taste and Chemosensory BehaviorGENDER DIFFERENCES IN ACTIVATION WITHIN THE OFCIN RESPONSE TO TASTE STIMULI WITH POSITIVE ORNEGATIVE VALANCE ARE RELATED TO HUNGER ANDSATIETYHaase L.B. 1 , Cerf-Ducastel B. 1 , Kemmotsu N. 1 , Green E. 1 , Jacobson A. 1 ,Miller M. 1 , Murphy C. 1 1 Psychology, San Diego State University, SanDiego, CAPrevious research supports the hypothesis that valance specific brainactivation related to positive and negative taste stimuli involves theorbital frontal cortex (OFC). The physiological states of hunger orsatiety influence behavior relating to the reward value of taste stimuli.This study employed fMRI to investigate cortical activation in responseto taste stimuli that are high and low in reward value when the subjectwas hungry or sated. A region of interest (ROI) analysis was conductedto test the hypothesis that gender differences in activation within theOFC to positive (sucrose) and negative (caffeine) stimuli are affected byhunger and satiety. Subjects rated the pleasantness of stimuli using thegLMS, (Bartoshuk et al., 2004) while stimuli were presented to themouth as 0.3ml boluses in distilled water. Imaging was conducted on a3T GE scanner. Image analysis was conducted using AFNI (Cox, 1996).Fit coefficients were subjected to ANOVA to compare the degree ofactivation in ROIs. Activation within the OFC in response to sucrose inthe hunger condition is greater for females than males. In contrast,activation in response to caffeine is greater in the sated condition forfemales than for males. These findings suggest that gender differencesin activation within the OFC in response to valence specific stimuli arerelated to hunger and satiety. Supported by NIH grants RO1AG04085to C.M and RO3DC05134 to B.C.D. We thank Dr. Giedrius Buracasand Dr. Lisa Eyler for their fMRI expertise.101