Hunger Modulates the Responses to Gustatory Stimuli of Single Neurons in the Caudolateral Orbitofrontal Cortex of the Macaque Monkey

1. In order to determine whether the responsiveness of neurons in the caudolateral orbitofrontal cortex (a secondary cortical gustatory area) is influenced by hunger, the activity evoked by prototypical taste stimuli (glucose, NaCl, HCl, and quinine hydrochloride) and fruit juice was recorded in single neurons in this cortical area before, while, and after cynomolgous macaque monkeys were fed to satiety with glucose or fruit juice. 2. It was found that the responses of the neurons to the taste of the glucose decreased to zero while the monkey ate it to satiety during the course of which his behaviour turned from avid acceptance to active rejection. 3. This modulation of responsiveness of the gustatory responses of the neurons to satiety was not due to peripheral adaptation in the gustatory system or to altered efficacy of gustatory stimulation after satiety was reached, because modulation of neuronal responsiveness by satiety was not seen at earlier stages of the gustatory system, including the nucleus of the solitary tract, the frontal opercular taste cortex, and the insular taste cortex. 4. The decreases in the responsiveness of the neurons were relatively specific to the food with which the monkey had been fed to satiety. For example, in seven experiments in which the monkey was fed glucose solution, neuronal responsiveness decreased to the taste of the glucose but not to the taste of blackcurrant juice. Conversely, in two experiments in which the monkey was fed to satiety with fruit juice, the responses of the neurons decreased to fruit juice but not to glucose. 5. These and earlier findings lead to a proposed neurophysiological mechanism for sensory-specific satiety in which the information coded by single neurons in the gustatory system becomes more specific through the processing stages consisting of the nucleus of the solitary tract, the taste thalamus, and the frontal opercular and insular taste primary taste cortices, until neuronal responses become relatively specific for the food tasted in the caudolateral orbitofrontal cortex (secondary) taste area. Then sensory-specific satiety occurs because in this caudolateral orbitofrontal cortex taste area (but not earlier in the taste system) it is a property of the synapses that repeated stimulation results in a decreased neuronal response. 6. Evidence was obtained that gustatory processing involved in thirst also becomes interfaced to motivation in the caudolateral orbitofrontal cortex taste projection area, in that neuronal responses here to water were decreased to zero while water was drunk until satiety was produced.     

Effects of hunger on the responses of neurons in the lateral hypothalamus to the sight and taste of food

Recordings were made from single neurons in the monkey lateral hypothalamus and substantia innominata which had previously been shown to respond with an increase or decrease of their firing rates when the hungry monkey tasted food, and/or when he looked at food. It was found that the responsiveness of these neurons to food decreased over the course of a meal of glucose as satiety increased. When satiety, measured by whether the monkey rejected the glucose, was complete, there was no response of the neurons to the taste and/or to the sight of glucose. The spontaneous firing rates of these cells were not affected by the transitions from hunger to satiety. This modulation of responsiveness to food of hypothalamic cells was specific to them in that it was not seen in cells in the globus pallidus which responded in relation to swallowing and mouth movements, or in cells in the visual inferotemporal cortex which responded when the monkey looked at the glucose-containing syringe. On the basis of this and other evidence it is suggested that the hypothalamic cells described here could be involved in the autonomic, the endocrine, and/or the feeding responses which occur when an animal sees or tastes food.     

Sensory-specific satiety: Food-specific reduction in responsiveness of ventral forebrain neurons after feeding in the monkey

It has been shown previously that some neurons in the lateral hypothalamus and substantia innominata respond to the sight of food, others to the taste of food, and others to the sight or taste of food, in the hungry monkey. It is shown here that feeding to satiety decreases the responses of hypothalamic neurons to the sight and/or taste of a food on which the monkey has been satiated, but leaves the responses of the same neurons to other foods on which the monkey has not been satiated relatively unchanged. This suggests that the responses of these neurons in the ventral forebrain are related to sensory-specific satiety, an important phenomenon which regulates food intake. In sensory-specific satiety, the pleasantness of the sight or taste of a food becomes less after it is eaten to satiety, whereas the pleasantness of the sight or taste of other foods which have not been eaten is much less changed; correspondingly, food intake is greater if foods which have not already been eaten to satiety are offered.     

Administration of satiety factors and gustatory responsiveness in the nucleus tractus solitarius of the rat.

The administration of certain factors associated with postprandial satiety decreases gustatory responsiveness. We compared the effects of intravenous injections of glucose, insulin, pancreatic glucagon (PG), and cholecystokinin (CCK) on multiunit activity evoked from taste responsive neurons in the nucleus tractus solitarius of rats. Glucose, insulin, and PG reliably suppressed evoked responses to lingual application of 1.0M glucose, whereas responses that followed CCK remained unchanged. A common physiological consequence of glucose, insulin, and glucagon is increased glucose availability which may impact directly on gustatory neurons or indirectly through modifications in ventral forebrain or vagal afferent activity.     

Taste neurons in the cortex of the alert cynomolgus monkey.

The activity of single neurons in the gustatory cortex of alert cynomolgus monkeys was analyzed. Taste-evoked activity in response to the four prototypical taste stimuli was recorded from a cortical gustatory area comprising the frontal operculum and adjoining anterior insula. Spontaneous activity for 364 gustatory neurons was 3.9 +/- 4.9 (mean +/- SD) spikes/s. Mean net (gross minus spontaneous) discharge rates for all gustatory neurons were: 1.0 M glucose = 4.9 +/- 11.6, 0.3 M NaCl = 3.2 +/- 7.1, M quinine HCl = 2.6 +/- 5.8, and 0.01 M HCl = 1.7 +/- 4.6. The results from intensity-response functions imply that the perception of each basic taste quality in the nonhuman primate is based on the activity of the appropriate neural subgroup rather than on the mean activity of all taste cells. Therefore a more meaningful index of the effectiveness of a stimulus may be the discharge rate it evokes from the subset of gustatory neurons for which it is the best stimulus. Glucose was the best stimulus for 142 cells (including ties), from which it elicited a mean net response of 10.3 spikes/s; NaCl was best for 107 neurons which gave a mean 8.7 spikes/s; quinine HCl evoked 6.2 spikes/s from the 74 cells that responded best to it; HCl elicited 5.9 spikes/s from the 49 neurons for which it served as best stimulus. The response characteristics of cortical taste cells indicate heterogeneous features, and significantly different patterns from those reported in other nonchemical sensory systems.     

Complex attributes of lateral hypothalamic neurons in the regulation of feeding of alert rhesus monkeys

To elucidate the roles of glucose-sensitive (GS) and glucose-insensitive (GIS) cells of the lateral hypothalamic area (LHA), single neuron activity was recorded during 1) microelectrophoretic administration of chemicals, 2) a conditioned bar press feeding task, 3) gustatory, 4) olfactory, and 5) electrical brain stimulation. GS and GIS neurons showed different firing rate changes during phases of the task, and the responses were highly influenced by the palatability of the food and the motivational (hunger or satiety) state of the animal. The two groups of cells also differed in their responsiveness to gustatory and olfactory stimuli: GS neurons were more likely to respond to tastes and odors than GIS cells. Taste- and odor-responsive GS neurons were primarily suppressed by electrophoretically applied noradrenaline and were localized ventromedially within the LHA. The chemosensitive GIS cells, being organized along a dorsolateral axis, were especially excited by dopamine. The two sets of neurons had distinct connections with associative (orbitofrontal, prefrontal) cortical areas. GS and GIS cells, thus, appear to have differential and complex attributes in the control of feeding.     

Convergence onto hamster medullary taste neurons

Research has shown that gustatory afferents innervating different areas of the oral cavity converge onto single neurons in the nucleus tractus solitarii (NTS). However, most studies of gustatory physiology have only stimulated the receptors on the anterior tongue. No information exists on the responses of hamster NTS neurons to stimulation of receptors located in other areas of the oral cavity. The present investigation compared responses of hamster NTS neurons to stimulation of receptors on the anterior tongue and posterior oral cavity, and to stimulation of both receptor populations together. Of the neurons, 64% responded to both anterior tongue and posterior oral cavity stimulation. The remaining neurons responded exclusively to stimulation of one area. Cells responsive to both fields of stimulation were found throughout the rostral NTS. Cells responding to stimulation of only one field were anatomically separate. Most neurons (69%) were more responsive to anterior tongue than posterior oral cavity stimulation. The neural responses to stimulation of both fields simultaneously were complex. Frequently, a cell's response was intermediate between those produced by stimulation of either receptor population alone. In other cases the response was the same as the larger of the two individual responses. The breadth of responsiveness to the 4 basic taste stimuli (sucrose, NaCl, HCl and quinine-HCl) was similar for both receptor populations, but the breadth of tuning of an individual cell for one field of stimulation was not correlated with its breadth of responsiveness for the other. In contrast, the breadth of tuning following stimulation of the entire oral cavity was correlated with that following stimulation of the anterior tongue.     

The effect of satiety on responses of gustatory neurons in the amygdala of alert cynomolgus macaques

An alert cynomolgus macaque was fed a sweet solution to satiety as the activity of a gustatory neuron in the amygdala was recorded to that solution and to four other taste stimuli. This experiment was conducted a total of 14 times in two monkeys. The responses of individual neurons to the satiety stimuli were suppressed by as little as 1%, and as much as 100% by the induction of satiety (mean suppression = 58%). Nine of the 14 cells responded to the satiety solution with excitation, and their responses were suppressed by a mean of 62% by satiety. Five neurons responded with inhibition, and their responses were suppressed by a mean of 50%. Responses to other taste stimuli, not associated with satiety, were affected to a lesser extent. The amygdala is a taste relay between the primary gustatory cortex, where satiety has no influence on responses to taste stimuli, and the lateral hypothalamic area where the effect of satiety is total. The data presented here indicate that the amygdala is a functional as well as anatomical intermediary between these two areas, and serves as a stage in the process through which sensory stimuli are imbued with motivational significance.     

Lateral hypothalamic modulation of oral sensory afferent activity in nucleus tractus solitarius neurons of rats

This study was designed to examine whether the sensory afferents from the anterior part of the tongue are modulated by activity of the lateral hypothalamic area (LHA) at the level of the nucleus tractus solitarius (NTS) in rats. The electrical activity of the NTS neurons was recorded extracellularly, and they were classified as gustatory, thermal, or mechanical neurons in accordance with their responsiveness to tongue stimulation by taste solutions, by warm and cool water, and by stroking the tongue surface. Sixty-two percent of the neurons were polysynaptically activated by electrical stimulation of the LHA. When a single conditioning stimulus of the LHA was applied prior to the test electrical stimulation of the tongue at various conditioning-test intervals, the activity of the gustatory neurons was facilitated by 30 to 80% of their control level for a period of approximately 20 to 150 msec. The activity of the mechanical and thermal neurons was suppressed for a 50- to 300-msec period. These results demonstrate the existence of modulatory effects from the LHA on the NTS neurons, which receive sensory information from the tongue.     

The Representation of Information About Taste and Odor in the Orbitofrontal Cortex

Complementary neurophysiological recordings in macaques and functional neuroimaging in humans show that the primary taste cortex in the rostral insula and adjoining frontal operculum provides separate and combined representations of the taste, temperature, and texture (including viscosity and fat texture) of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by learning with olfactory and visual inputs, and these neurons encode food reward in that they only respond to food when hungry and in that activations here correlate with subjective pleasantness and with individual differences in and cognitive modulation of the hedonic value of food. Information theory analysis shows a robust representation of taste in the orbitofrontal cortex, with an average mutual information of 0.45 bits for each neuron about which of six tastants (glucose, NaCl, HCl, quinine-HCl, monosodium glutamate, and water) was present, averaged across 135 gustatory neurons. The information increased with the number of neurons in the ensemble, but less than linearly, reflecting some redundancy. There was less information per neuron about which of six odors was present from orbitofrontal olfactory neurons, but the code was robust in that the information increased linearly with the number of neurons, reflecting independent information encoded by different neurons. Although some neurons were sharply tuned to individual tastants, the average encoding was quite distributed.     

Conditioned taste aversions modify neural responses in the rat nucleus tractus solitarius

Explorations of the neural substrates of conditioned taste aversions (CTAs) have focused principally on diencephalic and telencephalic structures. The nucleus tractus solitarius (NTS) is the initial gustatory relay in the rat's hindbrain. It is worthy of investigation for its part in mediating CTAs in that it is sensitive to several physiological conditions which affect feeding while also being a site of anatomical convergence for vagal afferents from the viscera and centrifugal projections from areas (hypothalamus, amygdala) implicated in emotions and hedonics. We compared single neuron responses from NTS to several taste stimuli in three groups of rats: (1) those receiving exposure to 0.0025 M sodium saccharin without physiological consequences; (2) those made ill through intraperitoneal injections of LiCl but having no obvious gustatory referent for their malaise (sensitization-pseudoconditioning controls); (3) those in which exposure to 0.0025 M sodium saccharin (the CS) was paired with LiCl-induced poisoning (the US), creating a pronounced aversion to the saccharin. According to response profiles, NTS neurons in all three groups could be divided into subsets of about 30%, which showed a sweet-sensitive profile, and 70%, which were primarily sensitive to nonsweet qualities. The major effect of the conditioning procedure was to increase responsiveness to the saccharin CS only among the sweet-sensitive subset. Moreover, the peak of activity which largely accounted for the increase occurred with a latency of 900 msec, perhaps implicating a secondary input to NTS from diencephalic or telencephalic sites. The significance of the results is that: (1) CTAs affect sensory activity at a lower order level than had heretofore been demonstrated; (2) NTS shows sensitivity to yet another physiological condition, reinforcing the involvement of the hindbrain in hedonics and sophisticated taste-related processes; (3) there is a subset of taste neurons, rather distinct according to its sensitivity profile, which is also functionally unique in its response to conditioning by a sweet CS.     

Regulating satiety in bulimia nervosa: the role of cholecystokinin

PURPOSE: Individuals with bulimia nervosa (BN) report altered perceptions in hunger, fullness, and satiety. This article reviews the role of cholecystokinin (CCK), a satiety‐producing hormone, in the regulation of binge eating in those who suffer from BN. CONCLUSION: Studies have shown that CCK is decreased in individuals with BN when compared with healthy controls. Decreased CCK functioning may contribute to impaired satiety and thus binge eating in this patient population. Depending on the macronutrient composition of food choices, CCK release can be differentially influenced. For instance, protein is a potent stimulator of a CCK response. Eating more protein‐rich meals increases the release of CCK, increasing satiety and ending a meal. PRACTICE IMPLICATIONS: Knowledge of CCK functioning and the utility of manipulating the macronutrient composition of meals may inform standard behavioral treatment strategies for those who suffer from BN.     

Cerebral processing of food-related stimuli: effects of fasting and gender

To maintain nutritional homeostasis, external food-related stimuli have to be evaluated in relation to the internal states of hunger or satiety. To examine the neural circuitry responsible for integration of internal and external determinants of human eating behaviour, brain responses to visual and complex gustatory food-related stimuli were measured using functional magnetic resonance imaging in 18 healthy non-smokers (10 women, 8 men). Each individual was studied on two occasions, the order of which was counterbalanced; after eating as usual and after 24 h fasting. Raised plasma free fatty acids and lower insulin and leptin concentrations confirmed that participants fasted as requested. When fasted, participants reported more hunger, nervousness and worse mood and rated the visual (but not gustatory) food-related stimuli as more pleasant. The effect of fasting on hunger was stronger in women than in men. No circuitry was identified as differentially responsive in fasting compared to satiety to both visual and gustatory food-related stimuli. The left insula response to the gustatory stimuli was stronger during fasting. The inferior occipito-temporal response to visual food-related stimuli also tended to be stronger during fasting. The responses in the occipito-temporal cortex to visual and in the insula to gustatory stimuli were stronger in women than in men. There was no interaction between gender and fasting. In conclusion, food reactivity in modality-specific sensory cortical areas is modulated by internal motivational states. The stronger reactivity to external food-related stimuli in women may be explored as a marker of gender-related susceptibility to eating disorders.     

Comparison of c-fos-like immunoreactivity in the brainstem following intraoral and intragastric infusions of chemical solutions in rats

To examine whether the activation of brainstem neurons during ingestion is due to orosensory afferents or post-ingestive factors, neuronal activation in response to intraoral and intragastric infusions of taste stimuli was compared in the area postrema (AP), nucleus tractus solitarius (NTS) and parabrachial nucleus (PBN) by the c-fos immunohistochemical method. An aliquot (7.5 ml) of 0.5 M sucrose, 5 mM sodium saccharin, 1 mM quinine hydrochloride and distilled water was delivered into the oral cavity or the stomach in each rat, which had been deprived of water and food overnight. Water induced little c-Fos-like immunoreactivity (c-FLI), but both intraoral and intragastric infusions of sucrose, but not non-caloric saccharin, induced strong c-FLI in the AP, caudal NTS and the external lateral subnucleus of the rostral PBN, suggesting that these areas receive general visceral inputs. Other areas in the NTS and PBN may receive gustatory inputs since more dominant c-FLI was detected by intraoral rather than intragastric infusions of the stimuli. Functional segregation of neurons reflecting qualitative and hedonic aspects of sweeteners (sucrose and saccharin) and bitter-tasting substance (quinine) was suggested in the PBN, but less evident in the NTS. These results indicate that c-fos induction in brainstem neurons during ingestion reflects gustatory inputs and postingestional factors depending on the kind of food ingested.     

Taste responses in the nucleus tractus solitarius of the chronic decerebrate rat

The ingestive behavior of decerebrate rats has been studied for some time, yet little is known of its neural substrates. While taste fibers in rats proceed from hindbrain to thalamus and ventral forebrain, these regions return centrifugal fibers to the hindbrain by which lower-order taste activity may be influenced. We examined the functional characteristics of taste neurons in the nucleus tractus solitarii (NTS) of chronic decerebrate rats in which this reciprocal communication was disrupted and compared them with those of intact controls. Nine Wistar rats were decerebrated at the supracollicular level. After a minimum of one week recovery, they were immobilized with Flaxedil, anesthetized locally and prepared for recording. The responses of 50 taste cells were isolated bilaterally from the NTS of these animals, while the activity of 50 additional neurons was recorded from 12 intact rats under the same conditions. Taste stimuli included 7 Na-Li salts, 3 sugars, HCl and citric acids, quinine HCl and NaSaccharin. Mean spontaneous activity in decerebrates was 6.5 spikes/s, 36.0% lower than the level in intact animals. Mean evoked activity was reduced by 32.6%. Analyses of the effects of stimulus quality, intensity and time course of the responses all indicated that the decrease in activity was attributable to the inability of taste cells in decerebrate rats to respond to demands for high discharge rates. This deficit could be responsible for the failure of these animals to develop conditioned taste aversions. Neurons from decerebrate preparations did, however, retain the broad sensitivity across stimuli that characterized taste cells in intact preparations. It was also typical that most neuron response profiles from decerebrates could be grouped into 3 loose clusters with peak sensitivities to acid-salt, salt or sugar. An analysis of similarities among stimulus activity profiles indicated that Na-Li salts, sugars and an acid-quinine complex represented 3 groups of stimulus quality; in intact animals, the primary distinction was between sweet and non-sweet stimuli. Moreover, the response to sodium saccharin lost its bitter component in decerebrates. These findings were in general agreement with those derived from acute decerebrate rats.     

Neuronal responses in monkey lateral hypothalamus during operant feeding behavior

Single neuron activity was recorded from monkey lateral hypothalamus to investigate neuronal events correlated with operant bar press feeding behavior. The behavioral paradigm was divided into three phase: visual (discrimination), bar press (procurement), and ingestion (consummatory). Of 669 neurons tested, 158 (24%) responded in one or more phases. During the visual phase, 106 neurons (16%) responded. Of 80 neurons that responded in the visual phase and were tested systematically, 33 (41%, 33/80) responded selectively to the sight of food or nonfood objects associated with a juice reward, but not to the sight of nonfood or objects associated with aversive saline. Neuronal activity related to discrimination was modulated by satiation and learning (i.e., acquisition and extinction). During the bar press phase, 51 neurons (7.6%) responded. These responded tonically during the early or late stage of the bar press period, but did not depend on individual bar pressing motions. During ingestion, 90 neurons (13%) responded. The ingestion response was modulated by palatability of food and satiation. Data suggest that the LHA is deeply involved in operant feeding behavior; discrimination of food, drive to get food, and perception of reward, all of which are affected by learning and internal states such as hunger and satiety.     

Effects of gustatory stimulation on brain activity during hunger and satiety in females with restricting-type anorexia nervosa: An fMRI study

Background

Previous research has demonstrated altered neuronal responses to visual stimulation with food in anorexia nervosa, varying with the motivational state of hunger or satiety. The aim of the present fMRI study was to assess hunger- and satiety-dependent alterations in the gustatory processing of stimulation with food in anorexia nervosa.

Methods

After food abstention (hunger condition) and after eating bread rolls with cheese (satiety condition), 12 females with restricting-type anorexia nervosa and 12 healthy females drank chocolate milk and water via a tube in a blocked design during image acquisition. Additionally, heart rate was registered during the measurements, and subjective ratings of hunger/satiety and of the valence of chocolate milk were assessed using a Likert scale.

Results

In participants with anorexia nervosa, drinking chocolate milk in the hunger condition induced significant activations in the right amygdala and in the left medial temporal gyrus relative to healthy controls. When contrasting neuronal responses to drinking chocolate milk during satiety with those evoked during hunger, a significant activation was found in the left insula in healthy controls, whereas in participants with anorexia nervosa, neuronal activity in the inferior temporal gyrus, covering the extrastriate body area, was observed.

Conclusions

Neuronal responses evoked by gustatory stimulation differ depending on hunger and satiety. Activations located in the amygdala and in the extrastriate body area might reflect fear of weight gain, representing one of the core symptoms of anorexia nervosa.     

Taste responses in the superior secondary gustatory nucleus of the carp, cyprinus carpio L.

Single unit discharges in the superior secondary gustatory nucleus of the carp, Cyprinus carpio L., were studied electrophysiologically in response to chemical stimulation of the external chemoreceptors of the facial skin surface.Of 36 gustatory neurons recorded, 80.6% were facilitated by taste stimuli and 19.4% were inhibited. The gustatory neurons were classified according to their responsiveness to the 4 basic taste substances and, except the inhibitory type, did not differ remarkably from the primary and secondary gustatory neurons. More inhibitory type (19.4%) neurons occurred at higher levels of the gustatory system. As in the primary and secondary levels, sodium chloride and acetic acid solutions were more effective stimuli than quinine HCl and sucrose.The ascending secondary gustatory fibers project bilaterally to the superior gustatory nucleus of the carp. About 20% of the gustatory neurons respond to stimulation of only the contralateral facial skin while 27.8% respond to stimulation of either side of the face. The latter neuron type showed very complicated responses, and were classified into ‘Uniform’, ‘Summation’, ‘Contra.Ipsi.’ and ‘Quality field’ types. The remaining 50% of the neurons respond only to stimulation on the ipsilateral side.     

Gustatory-salivary reflex: neural activity of sympathetic and parasympathetic fibers innervating the submandibular gland of the hamster

Electrophysiological experiments were performed to clarify the neural control mechanisms subserving gustatory-salivary reflex in anesthetized and decerebrate hamsters. Efferent neural activities of postganglionic sympathetic and preganglionic parasympathetic fibers, innervating the submandibular gland, were recorded when taste stimuli were infused into the oral cavity. Neural activities of primary gustatory afferents were also recorded from the chorda tympani (innervating the anterior part of the tongue) and the glossopharyngeal nerve (innervating the posterior part of the tongue). The parasympathetic fibers showed a low rate of spontaneous discharges (about 0.3 Hz), and responded tonically in an excitatory manner to taste stimulation. The magnitude of parasympathetic activity was highly correlated with the magnitude of gustatory afferent responses of the chorda tympani rather than that of the glossopharyngeal nerve. On the other hand, the sympathetic fibers showed irregular burst discharges (1.5 burst/s), and the rate of burst discharges was increased in response to high concentrations of HCl (0.03 M) or NaCl (1 M) solutions. Deafferentation experiments suggest that the parasympathetic activity is mainly influenced by gustatory information via the chorda tympani, while the sympathetic activity can be evoked by both the chorda tympani and glossopharyngeal nerve.     

Role of the central amygdaloid nucleus in shaping the discharge of gustatory neurons in the rat parabrachial nucleus

The central amygdaloid nucleus (CeA) receives projection from the parabrachial nucleus (PBN) gustatory neurons and descendingly projects to the PBN. To assess if the CeA is involved in modulating the activity of gustatory neurons in the PBN, the effects of electrical stimulation and electrolytic lesion of CeA on PBN gustatory neurons were observed. Of 60 neurons observed, 30 were classified as NaCl-best, 18 as HCl-best, 5 as Quinine HCl (QHCl)-best, and 7 as sucrose-best. During CeA stimulation, the responses to at least one effective stimulus were inhibited in most PBN neurons, with the response magnitudes to HCl and QHCl significantly decreased (P<0.01). In contrast, bilateral lesions of CeA facilitated the responses to HCl and QHCl (P<0.01). According to the best-stimulus category, the effects on the responses to HCl and QHCl were similarly subjected to these modulations either during electrical stimulation or after electrolytic lesions of CeA. Analyses of across-unit patterns indicated that the CeA stimulation increased the chemical selection of PBN taste neurons while the CeA lesions depressed the effect on the chemical selection between NaCl and QHCl. These findings suggest that the CeA may be involved in mediating feeding behavior via modulating the activity of gustatory neurons of PBN.