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 parameter 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 somatosen-sory, 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-tempo-ropolar component of the paralimbic brain should be considered as an integrated unit of cerebral organization.     

Selective deficit of mental visual imagery with intact primary visual cortex and visual perception

There is a vigorous debate as to whether visual perception and imagery share the same neuronal networks, whether the primary visual cortex is necessarily involved in visual imagery, and whether visual imagery functions are lateralized in the brain. Two patients with brain damage from closed head injury were submitted to tests of mental imagery in the visual, tactile, auditory, gustatory, olfactory and motor domains, as well as to an extensive testing of cognitive functions. A computerized mapping procedure was used to localize the site and to assess the extent of the lesions. One patient showed pure visual mental imagery deficits in the absence of imagery deficits in other sensory domains as well as in the motor domain, while the other patient showed both visual and tactile imagery deficits. Perceptual, language, and memory deficits were conspicuously absent. Computerized analysis of the lesions showed a massive involvement of the left temporal lobe in both patients and a bilateral parietal lesion in one patient. In both patients the calcarine cortex with the primary visual area was bilaterally intact. Our study indicates that: (i) visual imagery deficits can occur independently from deficits of visual perception; (ii) visual imagery deficits can occur when the primary visual cortex is intact and (iii) the left temporal lobe plays an important role in visual mental imagery.     

Multisensory Convergence in the Orbital and Ventrolateral Prefrontal Cortex

The prefrontal cortex can be divided into at least five distinct networks or systems, which have preferential intrinsic connections with other areas in the same system and distinct connections with other parts of the brain. Of these, the orbital network and the ventrolateral prefrontal cortex both receive multimodal sensory inputs and appear to function as regions for integration of this information, with an important role in the assessment of sensory objects or stimuli. The orbital network receives prominent olfactory, taste, and visceral inputs, as well as visual and somatosensory inputs; it is probably especially important for assessment of food. The ventrolateral prefrontal region does not receive olfactory or taste visceral inputs but does receive the same visual and somatosensory inputs, as well as auditory inputs. It may serve a role in the assessment of nonfood objects.     

Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex

Flavor perception requires the neural integration of olfactory, gustatory and, possibly, visceral afferent information. Presently, it is not known where, or how this integration takes place in the brain. Neuroanatomical data presented here suggest that pathways subserving these sensory modalities converge in mouse insular cortex after surprisingly few synaptic relays. Orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to label main olfactory bulb (MOB) efferents. A projection into layer I of insular cortex was present in every case. Bulb transections were made to provoke anterograde degeneration and EM analysis confirmed that the olfactory projection to insular cortex was a terminal pathway. WGA-HRP injections in the MOB-recipient zone of insular cortex resulted in ortho and retrograde labeling of ascending and descending gustatory-visceral afferent pathways. It is concluded that in the mouse, there is a remarkably direct convergence of olfactory and gustatory-visceral sensory pathways in insular cortex. Together with the descending connections from insular cortex to the amygdala and to brainstem autonomic structures, it is possible that the cortical integration of olfactory and gustatory-visceral information could modulate mechanisms involved in food selection and autonomic reactions relating to the chemical senses. Basic mechanisms subserving flavor perception might be usefully modelled in mouse insular cortex.     

Orosensory and Homeostatic Functions of the Insular Taste Cortex

The gustatory aspect of the insular cortex is part of the brain circuit that controls ingestive behaviors based on chemosensory inputs. However, the sensory properties of foods are not restricted to taste and should also include salient features such as odor, texture, temperature, and appearance. Therefore, it is reasonable to hypothesize that specialized circuits within the central taste pathways must be involved in representing several other oral sensory modalities in addition to taste. In this review, we evaluate current evidence indicating that the insular gustatory cortex functions as an integrative circuit, with taste-responsive regions also showing heightened sensitivity to olfactory, somatosensory, and even visual stimulation. We also review evidence for modulation of taste-responsive insular areas by changes in physiological state, with taste-elicited neuronal responses varying according to the nutritional state of the organism. We then examine experimental support for a functional map within the insular cortex that might reflect the various sensory and homeostatic roles associated with this region. Finally, we evaluate the potential role of the taste insular cortex in weight-gain susceptibility. Taken together, the current experimental evidence favors the view that the insular gustatory cortex functions as an orosensory integrative system that not only enables the formation of complex flavor representations but also mediates their modulation by the internal state of the body, playing therefore a central role in food intake regulation.     

Hearing shapes our perception of time: temporal discrimination of tactile stimuli in deaf people

Confronted with the loss of one type of sensory input, we compensate using information conveyed by other senses. However, losing one type of sensory information at specific developmental times may lead to deficits across all sensory modalities. We addressed the effect of auditory deprivation on the development of tactile abilities, taking into account changes occurring at the behavioral and cortical level. Congenitally deaf and hearing individuals performed two tactile tasks, the first requiring the discrimination of the temporal duration of touches and the second requiring the discrimination of their spatial length. Compared with hearing individuals, deaf individuals were impaired only in tactile temporal processing. To explore the neural substrate of this difference, we ran a TMS experiment. In deaf individuals, the auditory association cortex was involved in temporal and spatial tactile processing, with the same chronometry as the primary somatosensory cortex. In hearing participants, the involvement of auditory association cortex occurred at a later stage and selectively for temporal discrimination. The different chronometry in the recruitment of the auditory cortex in deaf individuals correlated with the tactile temporal impairment. Thus, early hearing experience seems to be crucial to develop an efficient temporal processing across modalities, suggesting that plasticity does not necessarily result in behavioral compensation.     

The insula (Island of Reil) and its role in auditory processing: Literature review

The insular cortex is a complex structure which contains areas that subserve visceral sensory, motor, vestibular, and somatosensory functions. The role of the insular cortex in auditory processing was poorly understood until recently. However, recent case studies indicate that bilateral damage to the insulae may result in total auditory agnosia. Functional imaging studies demonstrate that the insulae participate in several key auditory processes, such as allocating auditory attention and tuning in to novel auditory stimuli, temporal processing, phonological processing and visual–auditory integration. These studies do not clarify the issue of further specialisation within the insular cortex, e.g. whether the posterior insulae are primarily sensory areas, while the anterior insulae serve mainly as integration/association auditory areas, two hypotheses that would be compatible with the cytoarchitectonic structure and connectivity of the insulae. The functional characterisation of the insulae remains incomplete, underlining the need for further studies.     

Cortical and subcortical projections to primary visual cortex in anophthalmic,enucleated and sighted mice

The purpose of this study was to identify and compare the afferent projections to the primary visual cortex in intact and enucleated C57BL/6 mice and in ZRDCT/An anophthalmic mice. Early loss of sensory‐driven activity in blind subjects can lead to activations of the primary visual cortex by haptic or auditory stimuli. This intermodal activation following the onset of blindness is believed to arise through either unmasking of already present cortical connections, sprouting of novel cortical connections or enhancement of intermodal cortical connections. Studies in humans have similarly demonstrated heteromodal activation of visual cortex following relatively short periods of blindfolding. This suggests that the primary visual cortex in normal sighted subjects receives afferents, either from multisensory association cortices or from primary sensory cortices dedicated to other modalities. Here cortical afferents to the primary visual cortex were investigated to determine whether the visual cortex receives sensory input from other modalities, and whether differences exist in the quantity and/or the structure of projections found in sighted, enucleated and anophthalmic mice. This study demonstrates extensive direct connections between the primary visual cortex and auditory and somatosensory areas, as well as with motor and association cortices in all three animal groups. This suggests that information from different sensory modalities can be integrated at early cortical stages and that visual cortex activations following visual deprivations can partly be explained by already present intermodal corticocortical connections.     

Neural substrates of tactile object recognition: an fMRI study

A functional magnetic resonance imaging (fMRI) study was conducted during which seven subjects carried out naturalistic tactile object recognition (TOR) of real objects. Activation maps, conjunctions across subjects, were compared between tasks involving TOR of common real objects, palpation of "nonsense" objects, and rest. The tactile tasks involved similar motor and sensory stimulation, allowing higher tactile recognition processes to be isolated. Compared to nonsense object palpation, the most prominent activation evoked by TOR was in secondary somatosensory areas in the parietal operculum (SII) and insula, confirming a modality-specific path for TOR. Prominent activation was also present in medial and lateral secondary motor cortices, but not in primary motor areas, supporting the high level of sensory and motor integration characteristic of object recognition in the tactile modality. Activation in a lateral occipitotemporal area associated previously with visual object recognition may support cross-modal collateral activation. Finally, activation in medial temporal and prefrontal areas may reflect a common final pathway of modality-independent object recognition. This study suggests that TOR involves a complex network including parietal and insular somatosensory association cortices, as well as occipitotemporal visual areas, prefrontal, and medial temporal supramodal areas, and medial and lateral secondary motor cortices. It confirms the involvement of somatosensory association areas in the recognition component of TOR, and the existence of a ventrolateral somatosensory pathway for TOR in intact subjects. It challenges the results of previous studies that emphasize the role of visual cortex rather than somatosensory association cortices in higher-level somatosensory cognition.     

Cortical connections of the second somatosensory area and the parietal ventral area in macaque monkeys

To gain insight into how cortical fields process somatic inputs and ultimately contribute to complex abilities such as tactile object perception, we examined the pattern of connections of two areas in the lateral sulcus of macaque monkeys: the second somatosensory area (S2), and the parietal ventral area (PV). Neuroanatomical tracers were injected into electrophysiologically and/or architectonically defined locations, and labeled cell bodies were identified in cortex ipsilateral and contralateral to the injection site. Transported tracer was related to architectonically defined boundaries so that the full complement of connections of S2 and PV could be appreciated. Our results indicate that S2 is densely interconnected with the primary somatosensory area (3b), PV, and area 7b of the ipsilateral hemisphere, and with S2, 7b, and 3b in the opposite hemisphere. PV is interconnected with areas 3b and 7b, with the parietal rostroventral area, premotor cortex, posterior parietal cortex, and with the medial auditory belt areas. Contralateral connections were restricted to PV in the opposite hemisphere. These data indicate that S2 and PV have unique and overlapping patterns of connections, and that they comprise part of a network that processes both cutaneous and proprioceptive inputs necessary for tactile discrimination and recognition. Although more data are needed, these patterns of interconnections of cortical fields and thalamic nuclei suggest that the somatosensory system may not be segregated into two separate streams of information processing, as has been hypothesized for the visual system. Rather, some fields may be involved in a variety of functions that require motor and sensory integration.     

Complementary circuits connecting the orbital and medial prefrontal networks with the temporal, insular, and opercular cortex in the macaque monkey

The origin and termination of axonal connections between the orbital and medial prefrontal cortex (OMPFC) and the temporal, insular, and opercular cortex have been analyzed with anterograde and retrograde axonal tracers, injected in the OMPFC or temporal cortex. The results show that there are two distinct, complementary, and reciprocal neural systems, related to the previously defined "orbital" and "medial" prefrontal networks. The orbital prefrontal network, which includes areas in the central and lateral part of the orbital cortex, is connected with vision-related areas in the inferior temporal cortex (especially area TEav) and the fundus and ventral bank of the superior temporal sulcus (STSf/v), and with somatic sensory-related areas in the frontal operculum (OPf) and dysgranular insular area (Id). No connections were found between the orbital network and auditory areas. The orbital network is also connected with taste and olfactory cortical areas and the perirhinal cortex and appears to be involved in assessment of sensory objects, especially food. The medial prefrontal network includes areas on the medial surface of the frontal lobe, medial orbital areas, and two caudolateral orbital areas. It is connected with the rostral superior temporal gyrus (STGr) and the dorsal bank of the superior temporal sulcus (STSd). This region is rostral to the auditory parabelt areas, and there are only relatively light connections between the auditory areas and the medial network. This system, which is also connected with the entorhinal, parahippocampal, and cingulate/retrosplenial cortex, may be involved in emotion and other self-referential processes.     

Neural inputs into the temporopolar cortex of the rhesus monkey

Temporopolar cortex (TP) can be subdivided into agranular, dysgranular, and granular components. The telencephalic input into the temporopolar cortex arises from the orbitofrontal and medial frontal regions, modality-specific visual and auditory association areas, paralimbic regions, the piriform olfactory cortex, the hippocampus, the amygdala, the claustrum, and the basal forebrain. Afferents from limbic and paralimbic regions are directed mostly to the agranular and dysgranular sectors of the temporal pole, whereas afferents from isocortical association areas are distributed predominantly within the granular sector. The temporopolar cortex provides a site for the potential convergence of sensory and limbic inputs. Auditory inputs predominate in the dorsolateral part of the temporopolar cortex whereas visual inputs become prominent only in the ventral portions of this region. Olfactory inputs are directed mostly to the medial parts of the temporal pole. These medial parts also receive more extensive projections from the amygdaloid nuclei.     

Cortical and subcortical, including sensory-related, afferents to the thalamic mediodorsal nucleus of the cat

Cortical and subcortical afferents to the cat's thalamic mediodorsal nucleus (MD) were investigated using the method of retrograde transport of horseradish peroxidase (HRP). HRP was applied using vertical or oblique approaches and either a microsyringe or implanted pipettes filled with HRP-powder. A wide variety of cortical afferents to MD was detected: Aside from afferents from the cat's classical prefrontal cortex (gyri proreus, rectus, frontalis), from adjacent areas of the premotor and cingulate cortex and from portions of the insular cortex, afferents were found from cortical areas related to the processing of somatosensory, gustatory, auditory and visual information and from portions of the parietal and temporal association cortex. A considerable number of afferents arose from the diagonal band of Broca and a small number from the precommissural septum, periamygdaloid , prepiriform , entorhinal, subicular and amygdalar regions. The preoptic region and hypothalamic areas contained some labeled cells. All brains, with the exception of one with a very small dorsomedial injection, contained labeled cells in the mamillary bodies. The reticular nuclear complex and the ventral lateral geniculate nucleus were the main sources of afferents on the thalamic level. In the brain stem the substantia nigra, the ventral tegmental area, the deep layers of the superior colliculus, pretectal and tegmental regions contained labeled cells. These results show that MD receives afferents from a large variety of structures. Among them are several cortical as well as subcortical regions related to the processing of sensory and motor information. Taken together, these connections and the numerous afferents to MD from regions related to emotional and motivational behavior confirm the view that MD has to be termed association nucleus.     

The fiber connections of the temporal lobe with emphasis on the rhesus monkey

The temporal lobe has three functionally distinct areas which have minimal interconnections within the lobe, but extensive connections with other parts of the brain. The superior temporal gyrus contains primary and association auditory areas. Inferotemporal cortex is exclusively a visual association area. The temporal pole is involved in social behavior. In addition, the superior temporal sulcus functions as a sensory integration area. From a review of the literature, a schema is proposed for organizing the reciprocal connections of the three functional areas into a series of loops which follow both cortical and subcortical routes. The afferent and efferent connections of the temporal lobe, phylogenesis, and deficits from lesions are discussed.     

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.     

Sensory and premotor connections of the orbital and medial prefrontal cortex of macaque monkeys

Sensory and premotor inputs to the orbital and medial prefrontal cortex (OMPFC) were studied with retrograde axonal tracers. Restricted areas of the lateral and posterior orbital cortex had specific connections with visual-, somatosensory-, olfactory-, gustatory-, and visceral-related structures. More medial areas received few direct sensory inputs. Within the lateral and posterior orbital cortex, area 121 received a substantial projection from visual areas in the inferior temporal cortex (TE). Area 12m received somatosensory input from face, digit, or forelimb regions in the opercular part of area 1–2, in area 7b, in the second somatosensory area (SII), and in the anterior infraparietal area (AIP). Areas 13m and 131 also received a projection from the opercular part of areas 1–2 and 3b. The posteromedial and lateral agranular insular areas (Iapm and Ial, respectively) received fibers from the ventral part of the parvicellular division of the ventroposterior medial nucleus of the thalamus (VPMpc) that may represent a visceral afferent system. The dorsal part of VPMpc projected to the adjacent gustatory cortex. These restricted inputs from several sensory modalities and the convergent corticocortical connections to orbital areas 13l and 13m suggest a network related to feeding. The OMPFC was also connected to premotor cortex in ventral area 6 (areas 6va and 6vb), in cingulate area 24c, and probably in the supplementary eye field. Area 6va projected to area 12m, whereas a region of area 6vb projected to area 131. The region of the supplementary eye field projected to areas 121, 120, and 12r. Area lal received fibers from area 24c. Lighter and more diffuse projections also reached wider areas of the OMPFC. For example, injections in several orbital areas labeled a few cells scattered through the anterior part of area TE and the superior temporalrus. There was also a projection to the intermediate agranular insular area (Iai) and to areas 13a and 12o from the apparently multimodal areas in the superior temporal sulcus and gyrus. © 1995 Wiley-Liss, Inc.     

Cortical projections to the superior colliculus in grey squirrels (Sciurus carolinensis)

The superior colliculus is an important midbrain structure involved with integrating information from varying sensory modalities and sending motor signals to produce orienting movements towards environmental stimuli. Because of this role, the superior colliculus receives a multitude of sensory inputs from a wide variety of subcortical and cortical structures. Proportionately, the superior colliculus of grey squirrels is among the largest in size of all studied mammals, suggesting the importance of this structure in the behavioural characteristics of grey squirrels. Yet, our understanding of the connections of the superior colliculus in grey squirrels is lacking, especially with respect to possible cortical influences. In this study, we placed anatomical tracer injections within the medial aspect of the superior colliculus of five grey squirrels (Sciurus carolinensis) and analysed the areal distribution of corticotectal projecting cells in flattened cortex. V1 projections to the superior colliculus were studied in two additional animals. Our results indicate that the superior colliculus receives cortical projections from visual, higher order somatosensory, and higher order auditory regions, as well as limbic, retrosplenial and anterior cingulate cortex. Few, if any, corticotectal projections originate from primary motor, primary somatosensory or parietal cortical regions. This distribution of inputs is similar to the distribution of inputs described in other rodents such as rats and mice, yet the lack of inputs from primary somatosensory and motor cortex is features of corticotectal inputs more similar to those observed in tree shrews and primates, possibly reflecting a behavioural shift from somatosensory (vibrissae) to visual navigation.     

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.     

感觉刺激疗法在昏迷促醒治疗中的应用

感觉刺激疗法（sensory stimulation program,SSP）是应用一种或多种的感觉刺激,来促进昏迷患者苏醒的一种治疗方法;包括听觉刺激、视觉刺激、嗅觉刺激、味觉刺激、触觉刺激和体位刺激等,目前多用于外伤性昏迷（traumatic brain injury,TBI）。本文旨在评述SSP的特点和临床应用现状,为临床医生和患者家属提供更为确切有效的信息。