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PubMed1996

Orbitofrontal cortex neurons: role in olfactory and visual association learning.

1. The orbitofrontal cortex is implicated in the rapid learning of new associations between visual stimuli and primary reinforcers such as taste. It is also the site of convergence of information from olfactory, gustatory, and visual modalities. To investigate the neuronal mechanisms underlying the formation of odor-taste associations, we made recordings from olfactory neurons in the orbitofrontal cortex during the performance of an olfactory discrimination task and its reversal in macaques. 2. It was found that 68% of odor-responsive neurons modified their responses after the changes in the taste reward associations of the odorants. Full reversal of the neuronal responses was seen in 25% of these neurons. Extinction of the differential neuronal responses after task reversal was seen in 43% of these neurons. 3. For comparison, visually responsive orbitofrontal neurons were tested during reversal of a visual discrimination task. Seventy-one percent of these visual cells showed rapid full reversal of the visual stimulus to which they responded, when the association of the visual with taste was reversed in the reversal task. 4. These demonstrate that of many orbitofrontal cortex olfactory neurons on the taste with which the odor is associated. 5. This modification is likely to be important for setting the motivational value of olfactory for feeding and other rewarded behavior. However, it is less complete, and much slower, than the modifications found or orbit frontal visual during visual-taste reversal. This relative inflexibility of olfactory responses is consistent with the need for some stability is odor-taste associations to facilitate the formation and perception of flavors.

Acoustic Stimulation↗
PubMed2002

[Gustatory disturbance associated with putaminal hemorrhage].

48-year-old left-handed man experienced a sudden loss of taste, followed by dysarthria and dysphagia. Taste threshold examined by a small filter-paper disc method was severely elevated on both sides of the tongue. Brain CT revealed right putaminal hemorrhage that measured 9.3 ml in volume. In addition, brain MRI showed multiple cerebral infarcts bilaterally in the basal ganglia, and the corona radiata, and on the right side of the middle pontine tegmentum. His dysarthria and dysphagia seemed to be caused by interruption of bilateral cortico-bulbar tracts, and resolved within two weeks when edema around the hemorrhage regressed. The gustatory disturbance that persisted may be caused by the interruption of central gustatory pathways at the pons on one side, and subcortically close to the insular cortex on the other side.

Cerebral Infarction↗
PubMed1990

Development of the lateral and medial limbic cortices in the rat in relation to cortical phylogeny.

[3H]Thymidine autoradiography was used to investigate neurogenesis of the lateral limbic cortex and morphogenesis of the medial and lateral limbic cortices in adult and embryonic rat brains. Ontogenetic patterns in the limbic cortex are unique because some neurogenetic gradients are linked to those in neocortex, others are linked to those in paleocortex. These findings are related to hypotheses of cortical phylogeny. The experimental animals used for neurogenesis were the offspring of pregnant females injected with [3H]thymidine on 2 consecutive days: Embryonic Day (E) 13-E14, E14-E15, ...E21-E22, respectively. On Postnatal Day (P)60, the proportion of neurons originating during 24-h periods were quantified at nine anteroposterior levels and one sagittal level. Similar to neocortex, deep cells are generated earlier than superficial cells throughout the lateral limbic cortex: layer VI mainly on E14-15, layer V on E15-E16, and layers IV-II on E16-E18. There is a ventral/older to dorsal/younger neurogenetic gradient between the ventral agranular insular, dorsal agranular insular, and gustatory cortical areas and between ventral and dorsal orbital areas beneath the frontal pole. Similar to paleocortex below the rhinal sulcus, limbic cortex in the rhinal sulcus has a "sandwich" gradient: the older posterior agranular insular area is sandwiched by anterior and posterior younger areas (ventral agranular insular and perirhinal). To study morphogenesis, pregnant females were given single injections of [3H]thymidine during gestation and embryos were removed in successive 24-h intervals (sequential-survival). Neurogenesis finishes first in ventral limbic areas, later in dorsal limbic areas, and latest in neocortical areas. The cortical plate in the region of the medial and lateral limbic cortices does not have a separate subplate layer as is found in the region of the neocortex. Instead, layer VI in the limbic cortices has unusually older cells that are generated simultaneously with subplate cells.

Animals↗
PubMed2005

Medullary taste responses are modulated by the bed nucleus of the stria terminalis.

Previous studies have shown a modulatory influence of limbic forebrain areas, such as the central nucleus of the amygdala and lateral hypothalamus, on the activity of taste-responsive cells in the nucleus of the solitary tract (NST). The bed nucleus of the stria terminalis (BST), which receives gustatory afferent information, also sends descending axons to the NST. The present studies were designed to investigate the role of the BST in the modulation of NST gustatory activity. Extracellular action potentials were recorded from 101 taste-responsive cells in the NST of urethane-anesthetized hamsters and analyzed for a change in excitability following bilateral electrical stimulation of the BST. The response of NST taste cells to stimulation of the BST was predominately inhibitory. Orthodromic inhibitory responses were observed in 29 of 101 (28.7%) NST taste-responsive cells, with four cells inhibited bilaterally. An increase in excitability was observed in seven of the 101 (6.9%) NST taste cells. Of the 34 cells showing these responses, 25 were modulated by the ipsilateral BST and 15 by the contralateral; four were inhibited bilaterally and two inhibited ipsilaterally and excited contralaterally. The duration of inhibitory responses (mean = 177.9 ms) was significantly longer than that of excitatory responses (35.4 ms). Application of subthreshold electrical stimulation to the BST during taste trials inhibited or excited the taste responses of every BST-responsive NST cell tested with this protocol. NST neurons that were most responsive to sucrose, NaCl, citric acid or quinine hydrochloride were all affected by BST stimulation, although citric acid-best cells were significantly more often modulated and NaCl-best less often modulated than expected by chance. These results combine with excitatory and inhibitory modulation of NST neurons by the insular cortex, lateral hypothalamus and central nucleus of the amygdala to demonstrate extensive centrifugal modulation of brainstem gustatory neurons.

Animals↗
PubMed2001

Callosal connections of the cortical taste area in rats.

The granular and dysgranular insular subregions of the cortical taste area in rats are shown to connect anatomically with the homotopical regions in the opposite hemisphere through the corpus callosum. Cells of callosal efferents and terminals of callosal fibers were found in almost all cortical layers. The findings clarify the current understanding of the morphological substrate of callosal interactions in the gustatory system.

Animals↗
PubMed1976

Dependence of reward contingent positive variation (RCPV) and cortical synchronization on visual input in the cat.

Cats trained to press a lever for milk reward display high amplitude low frequency electrocorticographic post-reinforcement synchronization (PRS) associated with epicortical steady potential shift, termed Reward Contingent Positive Variation (RCPV), over the parieto-occipital cortex. Previously, it was found that the PRS-RCPV phenomenon depends on unpatterned light input devoid of any conceivable information or conditional property. Although training in the dark most likely eliminated the "novelty" factor and the resulting orienting reaction to "light off" as a cause of PRS-RCPV suppression, a possibility could not be excluded that the absence of light had a negatively reinforcing property preventing the emergence of PRS-RCPV. Hence, in the present study an experimental paradigm was used in which "light off" and/or "tone on" cues signalled the availability of reward, the "light off" periods extending through the consummatory response. Seven out of 9 cats, despite 2-4 months of daily training, and 85% correct timing of bar press performance, never showed a PRS-RCPV response (one animal showed only sporadic and poorly developed patterns.) However, when the light was turned on during consumption, in 85% of such tests a fully developed PRS-RCPV emerged in a stimulus-bound manner. One animal was an exception and showed PRS-RCPV both in the absence and presence of light. It was concluded that light input plays a crucial role in the emergence of the PRS-RCPV phenomenon and therefore also participates in the integration of gustatory input.

Animals↗
PubMed1982

Insula of the old world monkey. III: Efferent cortical output and comments on function.

The insula sends neural efferents to cortical areas from which it receives reciprocal afferent projections. A collective consideration of afferents and efferents indicates that the insula has connections with principal sensory areas in the olfactory, gustatory, somesthetic (SI and SII), and auditory (AI and AII) modalities. There are additional connections with association areas for the visual (TEm), auditory (supratemporal plane), and somesthetic (posterior parietal cortex) modalities; with paramotor cortex (area 6 and perhaps MII); with polymodal association cortex; and with a wide range of paralimbic areas in the orbital, temporopolar, and cingulate areas. The topographic distribution of these connections suggests that the posterodorsal insula is specialized for auditory-somesthetic-skeletomotor function whereas the anteroventral insula is related to olfactory-gustatory-autonomic function. Most of the insula, especially its anteroventral portions, have extensive interconnections with limbic structures. Through its connections with the amygdala, the insula provides a pathway for somatosensory, auditory, gustatory, olfactory, and visceral sensations to reach the limbic system. The cortical areas connected with the granular sector of the insula are also granular in architecture whereas virtually all the connections of the agranular insula arise from allocortical, agranular, or dysgranular areas. Thus, there is a correspondence between the architecture of insular sectors and the areas with which they have connections. The insula is heavily interconnected with temporopolar and lateral orbital areas. Furthermore, many cortical connections of the lateral orbital cortex are quite similar to those of the insula. These common connectivity patterns support the conclusion, based on architectonic observations, that the insulo-orbito-temporopolar component of the paralimbic brain should be considered as an integrated unit of cerebral organization.

Animals↗
PubMed2006

Eye closure in darkness animates olfactory and gustatory cortical areas.

In two previous fMRI studies, it was reported that eyes-open and eyes-closed conditions in darkness had differential effects on brain activity, and typical patterns of cortical activity were identified. Without external stimulation, ocular motor and attentional systems were activated when the eyes were open. On the contrary, the visual, somatosensory, vestibular, and auditory systems were activated when the eyes were closed. In this study, we investigated whether cortical areas related to the olfactory and gustatory system are also animated by eye closure without any other external stimulation. In a first fMRI experiment (n = 22), we identified cortical areas including the piriform cortex activated by olfactory stimulation. In a second experiment (n = 12) subjects lying in darkness in the MRI scanner alternately opened and closed their eyes. In accordance to previous studies, we found activation clusters bilaterally in visual, somatosensory, vestibular and auditory cortical areas for the contrast eyes-closed vs. eyes-open. In addition, we were able to show that cortical areas related to the olfactory and gustatory system were also animated by eye closure. These results support the hypothesis that there are two different states of mental activity: with the eyes closed, an "interoceptive" state characterized by imagination and multisensory activity and with the eyes open, an "exteroceptive" state characterized by attention and ocular motor activity. Our study also suggests that the chosen baseline condition may have a considerable impact on activation patterns and on the interpretation of brain activation studies. This needs to be considered for studies of the olfactory and gustatory system.

Attention↗
PubMed2004

Rostral agranular insular cortex and pain areas of the central nervous system: a tract-tracing study in the rat.

The rostral agranular insular cortex (RAIC) has recently been identified as a site where local changes in GABA and dopamine levels, or application of opioids, can alter nociceptive thresholds in awake animals. The connections of the cortex dorsal to the rhinal fissure that includes the RAIC have been examined previously, with emphasis on visceral and gustatory functions but not nociception. Here we examined the afferent and efferent connections of the RAIC with sites implicated in nociceptive processing. Sensory information from the thalamus reaches the RAIC via the submedius and central lateral nuclei and the parvicellular part of the ventral posterior nucleus. The RAIC has extensive reciprocal cortico-cortical connections with the orbital, infralimbic, and anterior cingulate cortices and with the contralateral RAIC. The amygdala, particularly the basal complex, and the nucleus accumbens are important targets of RAIC efferent fibers. Other connections include projections to lateral hypothalamus, dorsal raphe, periaqueductal gray matter, pericerulear region, rostroventral medulla, and parabrachial nuclei. The connectivity of the RAIC suggests it is involved in multiple aspects of pain behavior. Projections to the RAIC from medial thalamic nuclei are associated with motivational/affective components of pain. RAIC projections to mesolimbic/mesocortical ventral forebrain circuits are likely to participate in the sensorimotor integration of nociceptive processing, while its brainstem projections are most likely to contribute to descending pain inhibitory control.

Animals↗
PubMed2005

Somatosensory and pain responses to stimulation of the second somatosensory area (SII) in humans. A comparison with SI and insular responses.

Somatosensory and pain responses to direct intracerebral stimulations of the SII area were obtained in 14 patients referred for epilepsy surgery. Stimulations were delivered using transopercular electrodes exploring the parietal opercular cortex (SII area), the suprasylvian parietal cortex (SI area) and the insular cortex. SII responses were compared to those from adjacent SI and insular cortex. In the three areas we elicited mostly somatosensory responses, including paresthesiae, temperature and pain sensations. The rate of painful sensations (10%) was similar in SII and in the insula, while no painful sensation was evoked in SI. A few non-somatosensory responses were evoked by SII stimulation. Conversely various types of non-somatosensory responses (auditory, vegetative, vestibular, olfacto-gustatory, etc.) were evoked only by insular stimulation, confirming that SII, like SI, are mostly devoted to the processing of somatosensory inputs whereas the insular cortex is a polymodal area. We also found differences in size and lateralization of skin projection fields of evoked sensations between the three studied areas, showing a spatial resolution of the somatotopic map in SII intermediate between those found in SI and insula. This study shows the existence of three distinct somatosensory maps in the suprasylvian, opercular and insular regions, and separate pain representations in SII and insular cortex.

Adult↗
PubMed1989

Oral cavity representation at the frontal operculum of macaque monkeys.

Receptive properties of neurons at areas 3 and 1-2, and the gustatory area (area G) in the frontal operculum (Fop) and the neighboring areas were investigated in the cerebral cortex of Macaca irus and Macaca fuscata by applying mechanical and taste stimulation to the oral cavity and lips. Tactile neurons with different receptive properties were noted in areas 3, 1-2 and G. Areas 3 and G were packed with tongue neurons, though a considerable number of palate neurons were also found in area G, while area 1-2 was involved in representation of the tongue, palate, periodontia and lips. Both the anterior and posterior parts of the tongue were represented on these areas, and of the palate, the posterior part (the soft palate) was largely represented. The anterior and posterior periodontia were represented, without separation. Various tissues were represented with different laterality: Periodontia and the lips were most frequently represented bilaterally or contralaterally, but the tongue and palate often ipsilaterally. In area 6, the insula and other areas surrounding areas 3, 1-2 and G, tactile neurons were also found to have receptive fields on the lips, tongue, palate or periodontium, and the receptive fields on the tongue or palate were mainly bilateral. On the other hand, most of the taste neurons were located in area G and some in area 1-2 and the insula. The present study demonstrated that in macaque monkeys, tactile sensation of the oral cavity is represented on areas 3, 1-2 and G in the Fop as well as on the surrounding areas (e.g., area 6 and the insula), and taste sensation on areas G and 1-2 and the insula.

Animals↗
PubMed2007

C-fos expression in the rat brain following lithium chloride-induced illness.

The present study examined c-Fos expression in selected brain areas consequent to administration of lithium chloride, the typical illness-inducing agent used in laboratory studies of conditioned taste aversion. The results replicated previous findings of significant c-Fos expression in the parabrachial nucleus, the central nucleus of the amygdala and the basolateral amygdala. New findings indicate significant lithium-induced c-Fos in the gustatory region of the thalamus and the bed nucleus of the stria terminalis but not in the insular cortex. The results are discussed with respect to the neural substrates of conditioned taste aversion.

Animals↗