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PubMed1982

Insular cortex projection to the nucleus of the solitary tract and brainstem visceromotor regions in the mouse.

Anterograde transport of horseradish peroxidase (HRP) and HRP conjugated to wheat germ agglutinin (WGA-HRP) demonstrated a substantial, bilateral projection from insular cortex to the nucleus of the solitary tract (NTS) in the mouse. Injections that labeled the projection were restricted to the cortical sector homologous to taste-visceral cortex in the rat and label was antero- and retrogradely transported to several subcortical structures along ascending taste-visceral pathways. Multiple, small injections in this cortical region labeled fibers and terminals throughout the rostro-caudal extent of NTS. Small, single injection showed that the projection is topologically organized: Rostral points along the cortical strip project to rostral parts of NTS, intermediate points to the intermediate levels of NTS and caudal parts of the cortical field to caudal parts of NTS. In NTS the primary cranial nerve afferents distribute along a rostral to caudal gradient with the VII nerve rostral, the IX intermediate and the Xth caudal [2, 6, 37]. The present results indicate that the cortical sensory representation of these cranial nerve afferents reflects their topographic distribution in NTS. This suggests that there is an organized anatomical substrate by which the cerebral cortex may selectively influence the central processing of both gustatory and visceral afferent information in the primary CNS relay for these modalities. This insulofugal pathway also terminates in parts of NTS and additional medullary areas that contain preganglionic parasympathetic motoneurons. This appears to be the first anatomical demonstration of a projection from any part of the cerebral cortex to parasympathetic motor nuclei. The pathway provides a substantial direct channel by which higher cortical activity may modulate parasympathetic function.

Animals↗
PubMed1998

Aversive gustatory stimulation activates limbic circuits in humans.

Animal studies implicate the amygdala and its connections in the recognition of aversive stimuli. A recent PET study demonstrated that the human amygdala and left orbitofrontal cortex show substantial increases in regional cerebral blood flow (rCBF) during exposure to aversive odourants. To examine if aversive gustatory stimuli similarly activate these regions, nine healthy women tasted an aversive saline solution, pure water and chocolate while rCBF was measured with PET. The aversive saline condition, when contrasted with the water condition, increased activity in the right amygdala, left anterior orbitofrontal cortex, medial thalamus, pregenual and dorsal anterior cingulate, and the right hippocampus. The right amygdala, left orbitofrontal cortex and pregenual cingulate remained significantly activated when saline was compared with chocolate. The present results indicate that the amygdala and orbitofrontal cortex respond to aversive stimuli in both the olfactory and gustatory modalities, and highlight the role of the pregenual cingulate in negative emotional processing.

Adult↗
PubMed2000

Incomplete gustatory lateralization as shown by analysis of taste discrimination after callosotomy.

The lateral organization of the gustatory pathway in man is incompletely understood. Majority of the studies support an uncrossed projection from each side of the tongue to the cortex, but reports of an opposite crossed organization continue to appear in the neurological literature. We studied the lateral organization of the gustatory pathway in normal controls, a man with a complete callosal agenesis, and a man with a complete section of the corpus callosum, a right anterior-frontal lesion, and language in the left hemisphere. Sapid solutions were applied to one or the other side of the tongue, and subjects reported the taste of the stimulus either verbally or by manually pointing to the name of the taste. There were no differences in accuracy and reaction time between the right and left hemitongues of the controls and the genetically acallosal observer. By contrast, the callosotomy subject showed a constant marked advantage of the left hemitongue over the right for both accuracy and speed of response, though performance with right stimuli was clearly above chance. The left advantage can be attributed to the left hemisphere being favored by the essentially verbal nature of the task, or to the presence of a lesion in cortical gustatory areas in the right hemisphere, or to both factors. Whichever of these hypotheses turns out to be correct, the results unequivocally reject the notion of an exclusively crossed organization of the gustatory pathway from the tongue to the cortex, and favor the notion of a bilaterally distributed organization of this pathway with a marked predominance of the uncrossed over the crossed component.

Adult↗
PubMed1996

Hunger and satiety modify the responses of olfactory and visual neurons in the primate orbitofrontal cortex.

1. The primate orbitofrontal cortex is the site of convergence of information from primary taste and primary olfactory cortical regions. In addition, it receives projections from temporal lobe visual areas concerned with the representation of objects such as foods. Previous work has shown that the responses of gustatory neurons in the secondary taste area within the orbitofrontal cortex are modulated by hunger and satiety, in that they stop responding to the taste of a food on which an animal has been fed to behavioral satiation, yet may continue to respond to the taste of other foods. 2. This study demonstrates a similar modulation of the responses of olfactory and visual orbitofrontal cortex neurons after feeding to satiety. Seven of nine olfactory neurons that were responsive to the odors of foods, such as blackcurrant juice, were found to decrease their responses to the odor of the satiating food in a selective and statistically significant manner. 3. It also was found for eight of nine neurons that had selective responses to the sight of food, that they demonstrated a sensory-specific reduction in their visual responses to foods after satiation. 4. The responses of orbitofrontal cortex neurons selective for foods in more than one modality also were analyzed before and after feeding to satiation. Satiety often affected the responses of these multimodal neurons across all modalities, but a sensory-specific effect was not always demonstrable for both modalities. 5. These findings show that the olfactory and visual representations of food, as well as the taste representation of food, in the primate orbitofrontal cortex are modulated by hunger. Usually a component related to sensory-specific satiety can be demonstrated. The findings link at least part of the processing of olfactory and visual information in this brain region to the control of feeding-related behavior.

Analysis of Variance↗
PubMed1984

Thalamic connections of the insula in the rhesus monkey and comments on the paralimbic connectivity of the medial pulvinar nucleus.

Thalamic connections of the insula in the rhesus monkey were studied with axonal transport methods. Tritiated amino acid injections limited to the insula revealed autoradiographic label in the principal and parvicellular components of the ventroposterior medial nucleus, the ventroposterior inferior nucleus, the oral and medial pulvinar nuclei, the nucleus reuniens, the parvicellular and magnocellular components of the medial dorsal nucleus, the centromedian-parafasicularis nuclei, and the reticular nucleus. In additional animals, tritiated amino acids and horseradish perioxidase injections were made within different regions of the insula. Although the injection sites in these additional cases may have included minor extensions into claustrum and adjacent structures, several tentative conclusions emerged with respect to the antero-posterior gradient in insulothalamic connectivity. The anterior insula appears to have a more extensive relationship with the ventroposterior medial complex, the medial dorsal nucleus, the centromedian-parafasicularis nuclei and with some midline nuclei. In contrast, the posterior insula is more extensively connected with the ventroposterior inferior nucleus, the oral and medial pulvinar nuclei, and the suprageniculate nucleus. The patterns of insulothalamic connections support conclusions derived from observations on the cortical connectivity of the primate insular cortex indicating that the anterior insula is related to olfactory, gustatory, and viscero-autonomic behavior, whereas the posterior insula is related to auditory-somesthetic-skeletomotor function (Mesulam and Mufson, '82b). The medial pulvinar nucleus has extensive connections with many paralimbic cortical regions including the insula as well as with high order polymodal association cortex. These findings suggest that the medial pulvinar may provide a region for the convergence of multisensory association input with limbic information.

Animals↗
PubMed1988

Visceral cortex: integration of the mucosal senses with limbic information in the rat agranular insular cortex.

The organization of the subcortical and cortical connections of the rat agranular insular cortex was examined. Retrogradely transported dyes were used to map the agranular insular cortex efferents to brainstem visceral nuclei (the nucleus of the solitary tract and the parabrachial nucleus), to gustatory-visceral and limbic thalamic nuclei (medial ventrobasal and mediodorsal thalamus, respectively), and to association cortex (medial prefrontal and contralateral agranular insular cortex). The results revealed that a specific area within the ipsilateral agranular insular cortex projected to all of the subcortical and cortical areas listed above. This area of overlap in the agranular insular cortex stretched from the level of the genu of the corpus callosum rostrally to the crossing of the anterior commissure caudally. Anterograde projections from the medial ventrobasal and mediodorsal thalamus and from the olfactory bulb to the agranular insular cortex were mapped with wheat germ agglutinin conjugated to horseradish peroxidase. The terminal cortical projections from these areas were generally separate, except in an area where they overlap immediately medial to the rhinal fissure in the agranular insular cortex. This overlap area matched the area in the agranular insular cortex where there was an overlap of cortical efferent cells projecting to the brainstem, thalamus, and association cortex, as revealed in the retrograde tracing studies. We refer to this region of convergence in the agranular insular cortex as the visceral cortex, and suggest its involvement in the efficient integration of specific visceral sensory stimuli with correlated limbic or motivational consequences. The visceral cortex may help regulate the organism's visceral response to stress.

Animals↗
PubMed1999

Taste in the monkey cortex.

The sense of taste in humans differs substantially from that of rodents, from which a preponderance of gustatory electrophysiology derives. To establish a more appropriate neural model for human gustation, we recorded the activity of single neurons in the primary taste cortex in 11 alert cynomolgus macaques. Taste cells composed 6% of all neurons encountered. Another 24% responded during mouth and jaw movements, and 4% were sensitive to tactile stimulation of the mouth. Smaller numbers responded during olfactory or visual stimulation, or when the monkey extended his tongue. Taste cells could be divided into four statistically independent groups, corresponding to those most responsive to glucose (38%), NaCl (34%), quinine (22%), or HCI (5%). The location of a taste cell did not predict its response profile, i.e., there was no clear topographic organization of taste sensitivity. We established neural thresholds and intensity-response functions to the basic stimuli and determined that-with the exception of HCl, to which the macaque is relatively insensitive-they were similar to those reported by human subjects. We then turned to the coding of taste quality, as inferred in macaques from the patterns of neural activity elicited by each of greater than 100 stimuli. The results proved generally faithful to human reports of the perceived qualities of these same tastants. Finally, an investigation of taste mixtures revealed a degree of mixture suppression and interaction among basic qualities similar to those reported by humans. We conclude that the alert macaque offers a reliable neural model for human gustation.

Animals↗
PubMed2004

Reduced cortical noradrenergic neurotransmission is associated with increased neophobia and impaired spatial memory in aged rats.

In the present study, young (5-month-old (mo)) and aged (24 mo) adult male Fischer-344 (F344) rats were assigned to experimental groups based upon their performance of a reference memory task in the Morris water maze and reactivity to a novel palatable taste in a gustatory neophobia task. Levels of norepinephrine (NE) and its metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) were assayed via high performance liquid chromatography (HPLC) in brain regions associated with the locus coeruleus (LC)-hippocampus-cortex system and A1/A2-hypothalamic system. Binding of ligands specific for alpha-1, alpha-2, beta-1, and beta-2 receptors was assessed in hippocampus and cortex with receptor autoradiography. Impaired acquisition and retention of the water maze task and gustatory neophobia in aged rats was primarily associated with decreased NE activity in cingulate cortex (CC) as indicated by a significant reduction in the MHPG/NE ratio coupled with increased NE content. No significant changes in adrenergic receptor binding were detected in any region sampled. The results suggest that an aging-related reduction in cortical NE neurotransmission is associated with the expression of increased neophobia and deficits in spatial learning and memory performance occurring with advanced age in rats.

Adrenergic alpha-Agonists↗
PubMed2001

Functional magnetic resonance imaging of odor identification: the effect of aging.

BACKGROUND: Sense of smell declines with age and impairment in olfaction has been observed in some neurodegenerative disorders such as Alzheimer's disease. Functional neuroimaging techniques enable researchers to observe brain regions activated by olfactory stimuli. METHODS: We gave three mainly olfactory-mediated odors (limonene, methylsalicylate, and eugenol) to six young and six elderly subjects and observed the areas activated by using blood oxygen level dependent contrast functional magnetic resonance imaging. RESULTS: The group mapping of young subjects showed extensive activation in the orbitofrontal cortex, commonly believed to be the olfactory cortex, some limbic areas (the hippocampus and the thalamus), regions involved with gustatory sensation (the anterior insula and the inferior postcentral gyrus), superior and inferior temporal gyri, and cerebellum. In the elderly group, only the left inferior temporal gyrus and the primary visual cortex reached accepted significance levels. CONCLUSIONS: We have therefore confirmed previous reports of brain regions involved in olfactory processing in young volunteers and demonstrated decreased activation in elderly volunteers.

Adult↗
PubMed1995

Afferent connections of the caudolateral orbitofrontal cortex taste area of the primate.

A cortical taste region has recently been identified in the caudolateral orbitofrontal cortex of the macaque. The afferents to this region were investigated by means of retrograde tracing, using six injections of wheatgerm-conjugated horseradish peroxidase. The area of taste cortex was first identified physiologically in all the monkeys used in this anatomical study. The four injections into the middle and posterior part of this region resulted in large numbers of labelled cell bodies in the insular-opercular primary taste cortex. Following the two more anterior injections, label was found predominantly in the caudal part of the cardolateral orbitofrontal cortex itself. None of the injections resulted in labelled cells in the gustatory thalamic nucleus ventralis posterior medialis, pars parvocellularis, although all injections resulted in label of the mediodorsal nucleus of the thalamus. Afferents were also seen from more anterior parts of the orbitofrontal taste cortex, which may represent backprojections from subsequent taste areas. These results suggest that the caudolateral orbitofrontal cortex contains a higher-order taste cortex.

Amygdala↗
PubMed1989

Information processing in the taste system of primates.

1. Analysis of the activity of single neurones in the gustatory pathways in primates (cynomolgus monkeys) shows that the tuning of neurones to the four prototypical stimuli 1.0 mol l-1 glucose, 1.0 mol l-1 NaCl, 0.001 mol l-1 quinine-HCl and 0.01 mol l-1 HCl becomes sharper as information progresses through the taste system from the first central relay in the brainstem, the nucleus of the solitary tract, via the thalamus to the primary taste cortex in the frontal operculum and insula to reach a secondary cortical taste area in the caudolateral orbitofrontal cortex. 2. Feeding monkeys to satiety with glucose has no effect on the gustatory responses of neurones in the nucleus of the solitary tract, the frontal opercular taste cortex or the insular taste cortex, but decreases the magnitude of the neuronal responses of orbitofrontal cortex taste neurones which respond to glucose to zero. 3. The responses of orbitofrontal cortex taste neurones decrease to foods on which the monkey is fed to satiety, but continue to foods which have not just been eaten, that is, they reflect sensory-specific satiety, the phenomenon in which the pleasantness of the taste of a food and its acceptability, but not those of of other foods, is decreased by eating that food to satiety. 4. It has been found that the orbitofrontal cortex taste area or areas receives inputs from different modalities: single neurones with unimodal responses to taste (47%), olfactory (12%) and visual (10%) stimuli are found in close proximity to each other. Moreover, some single neurones show multimodal convergence, responding, for example, to taste and visual inputs (17%), taste and olfactory inputs (10%), and olfactory and visual inputs (4%). Some of these multimodal single neurones have corresponding sensitivities in the two modalities: they respond best to sweet tastes (e.g. 1 mol l-1 glucose), and respond more in a visual discrimination task to the visual stimulus which signifies sweet fruit juice than to that which signifies saline; or they respond to sweet taste and, in an olfactory discrimination task, to fruit juice odour. These results suggest that multimodal representations are formed in the orbitofrontal cortex secondary and related taste areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Gustatory neural coding in the amygdala of the alert macaque monkey.

1. Neurons in the amygdala are implicated in mediating hedonic appreciation, emotional expression, and conditioning, particularly as these relate to feeding. The amygdala receives projections from the primary taste cortex in monkeys, offering a route by which it could gain access to the gustatory information required to guide feeding behavior. We recorded the activity of 35 neurons in the amygdala of alert rhesus macaques in response to a range of gustatory intensities and qualities to characterize taste-evoked activity in this area. 2. The stimulus array comprised 26 chemicals, including four concentrations of each of the four basic taste stimuli, a series of other sugars, salts, and acids, monosodium glutamate, and orange juice. 3. Neurons responsive to taste stimulation could be found in a 76-mm3 region of the amygdala, centered 9.1 mm lateral to the midline, 14.9 mm anterior to the interaural line, and 25.7 mm below the surface of the dura. They composed 7.2% (35/484) of the cells tested for gustatory sensitivity in the amygdala. 4. The mean spontaneous activity of taste cells was 8.2 +/- 2.3 (SE) spikes per second. This rather high level provided an opportunity for reductions from spontaneous rate that was used regularly in the amygdala. When these negative response rates were included, the mean breadth-of-tuning coefficient of this sample of taste cells was 0.82. There was no strong evidence for gustatory neuron types, nor were functionally similar cells located together in a chemotopic arrangement. 5. Responses across 1.5 log units of stimulus concentration were nearly flat, with increasing excitation in some neurons largely offset by increasing inhibition in others. Taking the absolute value of the evoked activity, concentration-response functions rose monotonically to all basic stimuli except HCl, but were not sufficiently steep to account for human psychophysical data. The neural response to HCl did not rise with stimulus concentration within the range used. 6. Neural patterns representing the taste qualities of the basic stimuli were less sharply separated in the amygdala than at lower-order gustatory relays. Glucose elicited activity patterns that were most distinct from those of the nonsweet chemicals; those associated with NaCl were next most distinct. There was no clear separation between the patterns generated by chemicals that humans describe as sour and bitter. Monosodium glutamate evoked responses that did not correlate well with those of any basic stimulus, implying that its quality cannot be subsumed under the four basic tastes.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1993

A quantitative study of the differentiation of microglial cells in the developing cerebral cortex in rats.

The distribution of various morphological forms of microglia stained with lectin in different regions of postnatal rat brain was examined in 2 planes of section, coronal and sagittal. In the coronal sections (mediolateral plane) taken at the level of the optic chiasma, the lectin-labelled cells were examined in the gustatory (GU), lateral somatosensory (LSS), medial somatosensory (MSS), motor (MO) and cingulate (CI) cortex. In the sagittal sections (rostrocaudal plane), the lectin-labelled cells in the medial orbital (MOA), motor (MO) and primary visual area (PVA) were studied. The cells in the motor area in coronal plane were further analysed with reference to their distribution in each of the laminae (layers). Based on the variation of their external morphology which represents different degrees of differentiation, all lectin-labelled microglial cells of the above-mentioned regions in newborn (P0) and rats aged 4 d (P4) and 8 d (P8) postnatum were classified and quantified. In the mediolateral plane of any given age group, the most differentiated ramified cells were located in GU except in P8 rats where the cells were also concentrated in CI. Of the 3 regions in the rostrocaudal plane the majority of the more differentiated ramified cells at P0 were found in the PVA but were the major cell type in MO in P4 and P8 rats. For the distribution of cells in MO, the most differentiated cells were located in the intermediate zones. It was concluded from this study that microglial cells in the developing cerebrum showed a gradient of differentiation in relation to different regions of the cerebral cortex but this appeared to vary with age. Thus in the mediolateral plane in P0 and P4 rats, the gradient extended from GU to CI in a lateromedial fashion but in P8, in the direction towards MSS from GU and CI. In the sagittal section, the gradient was directed caudorostrally in P0 rats. In P4 and P8 rats, however, the gradient was from MO to both poles (MOA, PVA). In the motor cortex, the gradient was from the intermediate zone towards the superficial and deep laminae. The gradient of differentiation of microglia may be related to the growth of the respective regions in the cerebral hemisphere but inherent genetic factors were also considered.

Animals↗
PubMed1999

Conditioned enhancement of antibody production is disrupted by insular cortex and amygdala but not hippocampal lesions.

Pavlovian conditioning procedures can be used to activate the immune system. A reliable conditioned increase of antibody production can be obtained in rats that have previously received a gustative or odor stimulus as the conditioned stimulus paired with an antigen, by exposing the animals to the conditioned stimulus alone. We showed evidence that an excitotoxic lesion bilaterally applied into the insular cortex or the amygdala, but not into the dorsal hippocampus, impaired the acquisition of both odor and gustatory conditioned immune enhancement. We found no effects of lesions on normal antibody production. These results suggest that the amygdala and the insular cortex are involved in the neural-immune interactions that mediate conditioned immunity.

Amygdala↗
PubMed2000

The anatomical connections of the macaque monkey orbitofrontal cortex. A review.

The orbitofrontal cortex (OfC) is a heterogeneous prefrontal sector selectively connected with a wide constellation of other prefrontal, limbic, sensory and premotor areas. Among the limbic cortical connections, the ones with the hippocampus and parahippocampal cortex are particularly salient. Sensory cortices connected with the OfC include areas involved in olfactory, gustatory, somatosensory, auditory and visual processing. Subcortical structures with prominent OfC connections include the amygdala, numerous thalamic nuclei, the striatum, hypothalamus, periaqueductal gray matter, and biochemically specific cell groups in the basal forebrain and brainstem. Architectonic and connectional evidence supports parcellation of the OfC. The rostrally placed isocortical sector is mainly connected with isocortical areas, including sensory areas of the auditory, somatic and visual modalities, whereas the caudal non-isocortical sector is principally connected with non-isocortical areas, and, in the sensory domain, with olfactory and gustatory areas. The connections of the isocortical and non-isocortical orbital sectors with the amygdala, thalamus, striatum, hypothalamus and periaqueductal gray matter are also specific. The medial sector of the OfC is selectively connected with the hippocampus, posterior parahippocampal cortex, posterior cingulate and retrosplenial areas, and area prostriata, while the lateral orbitofrontal sector is the most heavily connected with sensory areas of the gustatory, somatic and visual modalities, with premotor regions, and with the amygdala.

Animals↗
PubMed2000

Cortical activation induced by intraoral stimulation with water in humans.

Studies of gustatory processing frequently utilize water as a control stimulus. However, the neural representations of intraoral stimulation with water have received little attention. We report a series of positron emission tomography studies involving intraoral stimulation with deionized distilled water. Attempting to taste water produced large, bilateral activations in insular, opercular, Rolandic and cerebellar cortices relative to resting with eyes closed or 'smelling' odorless air. The magnitude and volume of activation was substantially reduced when tasting water was contrasted with voluntary swallowing. This indicates that much of the activity induced by water reflects intraoral somatosensory or motor processing. Nevertheless, portions of the insula, operculum, post-central gyrus and cerebellum remained significantly activated in the contrast between 'tasting' water and swallowing. This activity appears to represent a specific neural correlate of fluid stimulation, and may reflect aspects of trigeminal, gustatory or thermal coding. These findings emphasize the large volume of cortex dedicated to intraoral processing, and highlight the importance of controlling for nongustatory factors in studies of gustation.

Administration, Oral↗
PubMed1999

Human cortical gustatory areas: a review of functional neuroimaging data.

In an effort to define human cortical gustatory areas we reviewed functional neuroimaging data for which coordinates standardized in Talairach proportional space were available. We observed a wide distribution of peaks within the insula and parietal and frontal opercula, suggesting multiple gustatory regions within this cortical area. Multiple peaks also emerged in the orbitofrontal cortex. However, only two peaks, both in the right hemisphere, were observed in the caudolateral orbitofrontal cortex, the region likely homologous to the secondary taste area described in monkeys. Overall significantly more peaks originated from the right hemisphere suggesting asymmetrical cortical representation of taste favoring the right hemisphere.

Brain Mapping↗