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PubMed1998

Forebrain contribution to the induction of a brainstem correlate of conditioned taste aversion. II. Insular (gustatory) cortex.

The induction of c-Fos-like immunoreactivity (c-FLI) in the intermediate division of the nucleus of the solitary tract (iNTS) has been shown to be a cellular correlate of the behavioral expression of a conditioned taste aversion (CTA). To further define neuroanatomical structures and pathways that contribute to this cellular response and to CTA learning in general, electrolytic lesions of insular (gustatory) cortex (IC) were combined with immunostaining for c-FLI. Rats were given either unilateral or bilateral electrolytic lesions of insular cortex or 'sham' operations. Following surgery, 'paired' animals were given a single conditioning trial consisting of intraoral infusion of 5-ml 0.15% sodium-saccharin followed by injection with LiCl (0.15 M, 20 ml/kg, i.p.) while 'unpaired' controls received a non-contingent saccharin-LiCl presentation. Rats with bilateral lesions showed no behavioral evidence of having acquired a CTA. Increases in c-FLI in iNTS were evident, but reduced, relative to 'sham' animals. Rats with unilateral-lesions displayed a CTA by rejecting the saccharin, although increases in c-FLI on the side of the iNTS ipsilateral to the lesion were reduced relative to that seen in 'sham' animals. A comparison of these results with those obtained after amygdala lesions supports the conclusion that amygdala and insular cortex are necessary, but not sufficient, for the behavioral expression of a CTA.

Animals↗
PubMed2004

7 to 12 Hz activity in rat gustatory cortex reflects disengagement from a fluid self-administration task.

The 7 to 12 Hz rhythm is a high-voltage oscillatory phenomenon recorded in many rat neocortical regions, largely analogous to the rodent and human somatosensory mu rhythm. Central to any interpretation of the functional significance of this pattern is the analysis of the behavioral context associated with it. Much of the debate on the function of mu, variously believed to represent either an environment-oriented or -isolated state, has relied primarily on its association with quiet immobility. In this report, we describe the relationship between the 7 to 12 Hz rhythm and a more complex behavioral setting, in which we were able to dissociated task orientation from disengagement. We trained head-restrained, water-restricted rats to perform a simple variant of a timed fluid self-administration task, while recording local field potentials from gustatory cortex (GC). Rats progressed through two behavioral states that were clearly distinguishable on the basis of lever-pressing regimes: a task-oriented state and a second state that reflected disengagement from the task. Concurrent GC neural recordings revealed bilaterally coherent oscillations in the 7 to 12 Hz range associated solely with the latter state. Consistent with published recordings of mu rhythm from somatosensory cortex, these rhythmic episodes were endogenously quenched when the rats prepared to lever-press; this inhibition of rhythmic episodes lasted through fluid delivery and consumption, making it clear that GC rhythms are not related to gustatory processing itself. By showing a direct relationship between the 7 to 12 Hz rhythm and disengagement from a task, these data provide strong and novel evidence that this gustatory rhythm in rats is associated with withdrawal from experimental contingencies.

Action Potentials↗
PubMed1994

Gustatory cortex of primates: anatomy and physiology.

Clinical and physiological studies of patients with ageusia or gustatory hallucination suggest that the primary gustatory area (area G) lies at the anterior insula or at the base of the central sulcus. However, physiological and anatomical studies in subhuman primates, e.g. squirrel monkeys or macaque monkeys, locate area G at the buried frontal operculum (Fop) and dorsal insula. The presence of secondary or higher gustatory areas are claimed because taste neurons are found in the precentral opercular area (PrCO) or orbitofrontal cortex in alert monkeys. Part of the anterior insula is suggested to subserve the interface between area G and the amygdala. Many physiological studies have been conducted lacking knowledge of the histological boundaries of the primary and secondary gustatory areas. Some difference has been found in the physiological properties of taste neurons in the primary and secondary gustatory areas: the primary gustatory area contains various categories of taste neurons, whereas most of the taste neurons in the secondary gustatory areas (e.g., PrCO, area 1-2) are specifically sensitive to one of the four basic tastes, and taste neurons in the orbitofrontal opercular area (OFO), another secondary gustatory area, show sensory-specific hunger as well.

Animals↗
PubMed1986

Gustatory cortex in the rat. I. Physiological properties and cytoarchitecture.

The precise cytoarchitectural localization of taste-elicited cortical responses in the rat was studied using a combination of anatomical and physiological techniques. Multi-unit responses to tongue tactile, thermal and gustatory stimuli were recorded along 97 electrode penetrations positioned parallel to the lateral convexity of the brain and marking lesions were placed at the sites of transitions in these functional properties. Lesions made at sites that received different sensory inputs were consistently located within different cytoarchitectural subdivisions. In this manner, taste cortex in the rat was localized to the agranular insular cytoarchitectural region, in contrast to its traditional assignation to granular insular cortex. Instead, tongue temperature was found to be represented in the cortical area previously termed gustatory, i.e., in ventral granular cortex where layer IV attenuates.

Afferent Pathways↗
PubMed1996

Ipsilateral connections between the gustatory cortex, amygdala and parabrachial nucleus are necessary for acquisition and retrieval of conditioned taste aversion in rats.

Acquisition and retrieval of conditioned taste aversion (CTA) is implemented by the interaction of several brain structures. In order to clarify the role of 3 important gustatory and visceral relays, gustatory neocortex (GC), amygdala (AM) and parabrachial nucleus (PB), two experimental series were carried out. In Expt. 1 reversible unilateral lesions of the PB and AM or of AM and GC were induced by 10 ng of tetrodotoxin (TTX) either in the same hemisphere or in the opposite hemispheres during CTA acquisition. It was found that contralateral TTX injections into the above structures caused a complete blockade of CTA acquisition which was not affected by ipsilateral TTX administration. In Expt. 2, retrieval of CTA acquired during unilateral blockade of the PB or AM in one hemisphere has been examined during unilateral TTX blockade of GC alone, AM alone or during combined GC and AM inactivation either in the same or in the contralateral hemispheres. A clear CTA retrieval impairment was found only when structures in the opposite hemispheres were blocked. These results indicate a complete lateralization of CTA acquisition and retrieval processes and suggest that the long-term CTA engram can be formed in each hemisphere separately without participation of the contralateral hemisphere.

Amygdala↗
PubMed2006

Empathy for positive and negative emotions in the gustatory cortex.

Anterior insula and adjacent frontal operculum (hereafter referred to as IFO) are active during exposure to tastants/odorants (particularly disgusting ones), and during the viewing of disgusted facial expressions. Together with lesion data, the IFO has thus been proposed to be crucial in processing disgust-related stimuli. Here, we examined IFO involvement in the processing of other people's gustatory emotions more generally by exposing participants to food-related disgusted, pleased and neutral facial expressions during functional magnetic resonance imaging (fMRI). We then exposed participants to pleasant, unpleasant and neutral tastants for the purpose of mapping their gustatory IFO. Finally, we associated participants' self reported empathy (measured using the Interpersonal Reactivity Index, IRI) with their IFO activation during the witnessing of others' gustatory emotions. We show that participants' empathy scores were predictive of their gustatory IFO activation while witnessing both the pleased and disgusted facial expression of others. While the IFO has been implicated in the processing of negative emotions of others and empathy for negative experiences like pain, our finding extends this concept to empathy for intense positive feelings, and provides empirical support for the view that the IFO contributes to empathy by mapping the bodily feelings of others onto the internal bodily states of the observer, in agreement with the putative interoceptive function of the IFO.

Emotions↗
PubMed1998

Functional lateralization of human gustatory cortex related to handedness disclosed by fMRI study.

Ten healthy subjects aged 20-25 including five right-handed and five left-handed according to the Dellatolas test participated in this functional magnetic resonance imaging (fMRI) study. A 3 Tesla whole-body MR scanner allowed echo planar imaging (EPI)-64 x 64 pixels, repetition time (TR) = 6 s, field of view (FOV) = 20 x 20 cm2--associated to acute anatomical localization of activated foci (256 x 256 pixels). Subjects were bilaterally stimulated with NaCl 85 mM, aspartame 2 mM, quinine hydrochloride 1 mM, glycyrrhizic acid 0.5 mM, guanosine monophosphate 1 mM and D-threonine 250 mM alternating with water. Stimuli and rinse were continuously pushed as bolus of 50 microliters every 3 s to the subject's mouth through microsyringes. We detected brain activated areas by correlation of the MR signal to an on-line perception profile recorded for each experiment and each subject with the finger-span method. We found most activations in the insula and the perisylvian region in agreement with previous electrophysiological studies on monkeys and clinical reports in humans. The superior part of the insula was bilaterally activated, in accordance with a whole-mouth stimulation. A striking lateralization related to handedness was found in a lower part of the insula. This projection in the dominant hemisphere, located in the same coronal plane as the upper insular activation, is the first evidence of a functional lateralization of brain processing involved in taste perception.

Adult↗
PubMed2004

Convergence of olfactory and gustatory connections onto the endopiriform nucleus in the rat.

Electrical and optical recordings were made from slice preparations including the piriform and gustatory cortices. Electrical stimulation of the gustatory cortex evoked a characteristic field potential in the endopiriform nucleus. A field potential was induced in the endopiriform nucleus by stimulation of the piriform cortex. Voltage-sensitive dye studies showed that stimulation of the piriform cortex induced signal propagation from the piriform cortex to endopiriform nucleus, whereas stimulation of the gustatory cortex did the same from the gustatory cortex to endopiriform nucleus via the agranular division of the insular cortex. After stimulation of the endopiriform nucleus, optical signals propagated not only to the piriform cortex but also to the gustatory cortex via the agranular division of the insular cortex. The olfactory and gustatory pathways appeared to be reciprocally connected. Unit recordings indicated that olfactory and gustatory activity converged onto a single neuron of the endopiriform nucleus. It is suggested that the cortical integration of olfactory and gustatory information could modulate mechanisms involved in food selection and emotional reactions relating to the chemical senses.

Animals↗
PubMedDate not supplied

Gustatory and olfactory contributions to alcohol consumption in rats.

To determine the relative contributions of taste and smell in the consumption of alcohol by rats, the present experiment tested normal rats (n = 14) and rats with either gustatory cortex ablations (n = 10), olfactory bulbectomies (n = 11), or combination gustatory cortex and olfactory bulb ablations (n = 12). Rats were tested under mild fluid deprivation using a two-bottle testing procedure. Thirteen concentrations of alcohol (0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, and 12%, v/v) were tested in ascending order. Results showed that at strong alcohol concentrations (7% through 11%) rats with combined gustatory cortex and olfactory bulb ablations consumed significantly more alcohol than normal control rats. Rats lacking gustatory cortex displayed a similar increased level of consumption with strong alcohol concentrations. It is suggested that the high level of consumption of strong alcohol concentrations by rats with central nervous system damage reflects an associative deficit rather than an alteration in taste or odor perception.

Alcohol Drinking↗
PubMed2004

Insular cortex lesions alter conditioned taste avoidance in rats differentially when using two methods of sucrose delivery.

The insular gustatory cortex may be essential for the evaluation of saliency and representation of the incentive values of tastes. Gustatory cortex lesions should interfere with conditioned taste avoidance according to these factors, which depend on the conditioned taste avoidance protocol used. The present study was aimed at investigating the effects of bilateral lesions of the gustatory cortex-focusing on electrolytic and excitotoxic lesions. Lesioned and sham-operated male Long-Evans rats were intoxicated using LiCl after drinking sucrose from a tube (SD) or having the same amount of sucrose fed directly into their mouths through a chronically implanted intra-oral (IO) cannula. Every aspect of the experiment was carefully counterbalanced between the experimental groups. In the control groups, the acquired avoidance towards sucrose was strongly preserved over eight extinction test days in SD rats but not in IO rats, in which a progressive decline was recorded. Electrolytic gustatory cortex lesions impaired but did not suppress conditioned taste avoidance in both protocols. Excitotoxic lesions tend to impair CTA also, but differentially according to the SD or IO protocols. Extinction of CTA was selectively impaired in the SD protocol by small lesions destroying the anterior insular cortex.

Animals↗
PubMed1992

Differential involvement of gustatory insular cortex and amygdala in the acquisition and retrieval of conditioned taste aversion in rats.

Lesion studies of the role of the gustatory insular cortex (GC) and amygdala (Am) in conditioned taste aversion (CTA) are confounded by the irreversibility of the intervention. Functional ablation methods allow more specific influencing of different phases of CTA acquisition and retrieval. Bilateral tetrodotoxin (TTX) blockade of GC (10 ng) or Am (3 ng) before or after saccharin drinking in rats with chronically implanted intracerebral cannulae showed that GC is indispensable for the initial processing of the taste stimulus but not for the association of the gustatory trace with the symptoms of LiCl poisoning. Gustatory signals can by-pass the blocked Am, the inactivation of which, however, impairs the gustatory trace-poisoning association. TTX injection into both GC and Am impairs CTA retrieval more than isolated blockade of either of these structures. It is argued that GC and Am implement processing of gustatory and visceral signals, respectively, but that formation and consolidation of the CTA engram proceeds outside forebrain, probably at the level of the brainstem.

Amygdala↗
PubMed1979

Electrophysiological analysis of retrieval of conditioned taste aversion in rats. Unit activity changes in critical brain regions.

Gustatory discrimination testing shows that rats with an overtrained conditioned taste aversion (CTA) to isotonic LiCl stop salt intake after 1 to 2 licks at the LiCl spout and move to the adjacent water spout within 0.7 s. Activity of 526 neurones from the nucleus of the solitary tract, gustatory thalamus, gustatory cortex, lateral and ventromedial thalamus, and amygdala was recorded in naive or CTA trained rats during the above gustatory discrimination. Post-stimulus histograms (PSH) triggered by water or salt licks or by spout switching were plotted for single units. Population responses of various regions were obtained by integration of the statistically significant excitatory and inhibitory intervals in the individual PSHs. Lick related changes of unit activity were orserved in 52% and 65% of neurones in control and CTA trained rats, respectively. The CTA training increased the incidence of units in which salt licking influenced the activity less than water licking. Presentation of the aversive fluid induced inhibition of unit activity in the gustatory cortex, ventromedial hypothalamus, and amygdala and excitation in the lateral hypothalamus. The changes started 100 to 150 ms after spout switching and culminated 100 ms later. Activity of the solitary tract nucleus and gustatory thalamus was affected less consistently. The results indicate that the gustatory cortex, amygdala and hypothalamus participate in CTA retrieval but a more specific identification of the electrical correlates of memory readout and of drinking control was not possible.

Action Potentials↗
PubMed1990

Aversive taste stimuli increase CGRP levels in the gustatory insular cortex of the rat.

Calcitonin gene-related peptide-like immunoreactivity (CGRP-IR) was surveyed immunohistochemically in the insular cortex of the rat, and the levels of insular cortical CGRP-IR were measured with the radioimmunoassay method following intraoral stimulation with various taste stimuli. CGRP-IR was localized in nerve fibers within the agranular and dysgranular insular cortices. The CGRP-IR levels in the rostral (gustatory) part of the insular cortex were increased significantly by strongly aversive taste stimuli such as quinine hydrochloride and conditioned taste stimuli (NaCl and sucrose) which animals had been taught to avoid. The results suggest that CGRP in the gustatory insular cortex is concerned with rejection or avoidance behaviors to aversive taste stimuli.

Animals↗