Prefrontal cortex is commonly defined as cortex which receives afferents from the thalamic mediodorsal nucleus (MD). The extent of opossum prefrontal cortex was mapped with anterograde and retrograde axonal transport methods. The prefrontal field was found to include not only cortex on the lateral convexity of the frontal lobe as reported in earlier studies, but, in addition, cortex within the rhinal fissure and cortex on the rostral medial wall of the hemisphere. The organization of the thalamic input to the medial wall was analyzed in some detail and compared with that of the rat. The reason for this emphasis stemmed from earlier observations which suggested that a lateral, nonolfactory segment of MD, prominent in the rat and other species, may not be present in opossum MD. In the rat, the lateral segment, which constitutes approximately one‐third of MD, projects to a relatively large expanse of rostral medial cortex which is also projected upon by the anteromedial nucleus. The main projection field of the lateral one‐third of opossum MD is to cortex on the lateral convexity of the frontal lobe which has no input from the anteromedial nucleus and has no counterpart in the rat. Only the most lateral edge of opossum MD projects to medial cortex, to a very small field, which is also projected upon by the anteromedial nucleus. In other respects, the organization of the rostral medial cortex is similar in rat and opossum. These results suggest that, rather than being absent, an equivalent of a nonolfactory segment may be present in opossum MD but is markedly reduced in size, compared to that in rat and other species.

Electrical stimulation of prefrontal cortex in anesthetized rabbits evoked small (< 10%) changes in heart rate. In contrast, stimulation of the thalamic mediodorsal nucleus (MD) elicited decreases in heart rate proportional to the stimulating current. The maximal peak reductions in heart rate evoked by higher current intensities were 85% from prestimulus levels. The bradycardiac response had a short latency after stimulus onset (< 1 s, peak within 5 s), and the heart rate usually returned to baseline within 30 s after stimulation. Vagal cholinergic innervation of the heart was suggested as the final effector pathway since bilateral vagotomy or administration of atropine (sulfate or methyl nitrate, 0.15–0.4 mg/kg, i.v.) virtually abolished the rapid bradycardiac responses. Administration of a β-adrenergic receptor blocker (propranolol, 3 mg/kg, i.v.) was without effect on the heart rate response. The effective medial thalamic area for evoking a response was localized to MD, the thalamic midline nuclei between both MDs and a region continuous with, but posterior to MD (e.g. parafascicular nucleus). A descending effector pathway from the thalamus was implicated since complete bilateral ablation of prefrontal cortex did not reduce the stimulus-produced bradycardia evoked from MD. Similar large bradycardiac responses were obtained in an unanesthetized preparation to both MD stimulation and to sensory stimuli, suggesting a possible physiological correlate for these intracranially-evoked heart rate changes.

Some sources of olfactory input to the opossum mediodorsal thalamic nucleus (MD) were identified by retrograde horserdish peroxidase and anterograde autoradiographic methods. One major source originated from the olfactorytubercle and a narrow strip of piriform cortex bordering the tubercle. The tubercle‐MD projection exhibited a definite spatial organization and included all except the most medial part of MD. The fact that the projection reached the most lateral and ventral extent of MD abutting the intralaminar complex suggests that the entire opossum MD may correspond to only the medial, magnocellular division in the primate and that the equivalents of both the parvocellular and paralamellar divisions may be absent.

Conclusions from lesion studies on the subcortical efferent connections of the thalamic mediodorsal nucleus have been varied and conflicting. In this autoradiographic study, tritiated proline was injected into the mediodorsal nucleus and adjacent midline nuclear areas (intermediodorsal nucleus and paraventricular nucleus of the thalamus) of 18 rabbits. Terminal labeling from injections that included parts of the paraventricular nucleus was seen in the following ipsilateral areas: central amygdaloid nucleus, lateral septum, a restricted portion of the nucleus of the stria terminalis, entorhinal cortex and the entire extent of the medial (periventricular) hypothalamus. Injections that encroached into the intermediodorsal nucleus produced ipsilateral labeling in most of the nucleus accumbens, layers II and III of the olfactory tubercle, the magnocellular portion of the posterolateral basal amygdaloid nucleus and the caudate nucleus. Injections restricted to the mediodorsal nucleus produced labeling only in the ipsilateral caudate nucleus.

The cortical projection of the thalamic mediodorsal nuclear complex (MD) in the rabbit was mapped with retrograde horseradish peroxidase and anterograde tritiated proline techniques. The projection field occupied the entire medial wall rostral to a mid corpus callosal level, wrapped around the frontal pole onto the lateral convexity and tailed off caudally on the dorsal bank of the rhinal sulcus. The projection of the lateral approximately one-half of MD, the half which does not receive olfactory input, was confined to medial cortex supplying all but the most rostral region. This projection field of lateral MD was precisely organized in two dimensions with the most lateral part projecting most caudally and the most dorsal part projecting most ventrally. A representation for the third, anterior-posterior (A-P), dimension was not evident since any cortical point within the field was supplied by a cylinder of cells extending the entire A-P extent of lateral MD. The medial half of MD, which does receive olfactory input, projected to the remaining rostral medial cortex, the lateral convexity and rhinal sulcal region. The inverse dorsoventral relationship was partially preserved and an overlapping A-P gradient was present with sulcal projections originating more caudally in medial MD and the rostral medial projection originating more rostrally.

Discharges of single cells in the thalamic mediodorsal nucleus (MD) of the opossum were recorded during electrical stimulation of the lateral olfactory tract. Responsive sites were histologically localized throughout the entire mediolateral extent of MD. In both rabbit and squirrel monkey responses are confined to the medial half of MD. Thus the lateral non-olfactory nuclear subdivision, common to both rabbit and squirrel monkey, was not found in the opossum. Firing patterns of cells were similar to those observed in rabbit and squirrel monkey. They commonly consisted of an early spike or burst of spikes, followed by a period of inactivity and then, in many cells, by a later period of response or of resumed spontaneous activity. The results indicate that olfactory input is characteristic of MD in a diverse sample of mammals but that topographic organization of the input is distinctly different in the opossum.

The thalamic mediodorsal nucleus (MD) of the squirrel monkey was explored with microelectrodes for units responsive to electrical stimulation of the olfactory bulb. All responsive units were localized throughout the magnocellular subdivision of MD, most (88%) ipsilateral to the stimulated bulb. Other parts of MD were unresponsive. Latencies to the first poststimulus spike ranged from 4 to 50 msec with a median value of 14 msec. In preparations with both frontal poles ablated eliminating the possibility of stimulus spread to orbitofrontal cortical neurons and subsequent anti- or orthodromic activation of Mc cells, the shortest response latency was 6 msec. Thus relatively direct and extensive connections exist between the olfactory bulb and one cytoarchitectonic subdivision of this prominent ‘association’ nucleus in a microsmatic primate.

The central gustatory pathways will be discussed in a progression, beginning with the first order terminations in the medulla oblongata, through the second order relay in the thalamus, and to the terminal projections in the cerebral cortex. The analysis of these central projections will be confined to the rat, cat, and primate. In each section consideration is first given to studies related to the localization of the gustatory projections and then, where data is available, to the characteristics of single and multiunit taste responses to adequate stimulation. An attempt has been made to maintain the historical transition of ideas within each section. Finally, some of the particular methodological problems associated with the gustatory system are outlined.

The involvement of the dorsal part of the caudal medulla in both the transmission and modulation of pain is supported by recent electrophysiological and anatomical data. In this review, we analyse the features of a well-delimited area within the caudal-most aspect of the medulla, the subnucleus reticularis dorsalis (SRD) which plays a specific role in processing cutaneous and visceral nociceptive inputs. From a general viewpoint, the reciprocal connections between the caudal medulla and spinal cord suggest that this area is an important link in feedback loops which regulate spinal outflow. Moreover, the existence of SRD-thalamic connections put a new light on the role of spino-reticulo-thalamic circuits in pain transmission.

Extracellular discharges were recorded from single neurons located in the ventrobasal thalamus of anesthetized squirrel monkeys. Units with receptive fields on glabrous skin of hand and foot were studied. Only one type of neuron was found that responded to temperature change. These units also responded to mechanical stimuli (T + M units). This finding contrasted with a previous investigation of tongue thalamic thermal projections where units specifically responsive to thermal stimuli were seen in addition to T + M units. This difference was discussed.

Cortex buried within the sylvian fissure of deeply anesthetized squirrel monkeys was probed with steel microelectrodes to record slow wave responses evoked by electrical stimulation of the three nerves innervating the tongue. A responsive locus was located in the most anterior opercular-insular cortex. Only stimulation of the two ipsilateral taste nerves (the chorda tympani and the lingual-tonsilar branch of the glossopharyngeal) was effective. Electrical stimulation of the contralateral taste nerves, the contra- and ipsilateral lingual nerves and mechanical stimulation of the tongue evoked no responses in this region.

The distribution of surface positive cortical potentials evoked by electrical stimulation of the three nerves innervating the tongue was mapped in deeply anesthetized squirrel monkeys. All projections were bilateral. In terms of extent of cortex activated, and the amplitude and latency of responses, the major projection of the two taste nerves (the chorda tympani and the lingual-tonsilar branch of the glossopharyngeal) was ipsilateral. The lingual nerve projections were bilaterally more symmetrical, but the shortest latencies were generated by contralateral stimulation. These laterality relationships were also found at the thalamic relay. All responses described in this report were confined to the appropriate part of the somatotopic pattern of somatic sensory area I, in the ipsi- and bilateral tactile representation of the intraoral structures. Complete bilateral ablation of the tongue nerve projection areas did not impair taste discrimination and did not cause retrograde degeneration of thalamic taste neurons. A subsequent study revealed a second taste nerve projection on opercular-insular cortex which, if included in the lesion, did result in complete degeneration of the thalamic taste relay. It was concluded that the taste system has only sustaining projections to S I of the squirrel monkey.

Neural mechanisms of taste.B Oakley, and R M BenjaminB Oakley, and R M BenjaminPublished Online:01 Apr 1966https://doi.org/10.1152/physrev.1966.46.2.173MoreSectionsPDF (6 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByGeniculate Ganglion Neurons are Multimodal and Variable in Receptive Field CharacteristicsNeuroscience, Vol. 367Characteristics of periodontal mechanoreceptors reinnervated after freezing the inferior alveolar nerveBrain Research, Vol. 536, No. 1-2Electron microscopic study of the effect of capsaicin on the mouse chorda tympani nervesArchives of Oral Biology, Vol. 35, No. 11The reinnervation of the tongue and salivary glands after lingual nerve injuries in catsBrain Research, Vol. 483, No. 2The origin of substance P in the rat submandibular gland and its major ductBrain Research, Vol. 252, No. 2The nature of the substance P-containing nerve fibres in taste papillae of the rat tongueNeuroscience, Vol. 7, No. 12Flavor enhances the antidipsogenic effect of naloxonePhysiology & Behavior, Vol. 28, No. 1Parabrachial area as mediator of bradycardia in rabbitsJournal of the Autonomic Nervous System, Vol. 4, No. 3Off-response in frog taste nerve and cell after stimulation of the tongue with bitter solutionsComparative Biochemistry and Physiology Part A: Physiology, Vol. 61, No. 2The seventh cranial nerve of the rat. Visualization of efferent and afferent pathways by cobalt precipitationBrain Research, Vol. 121, No. 1Intraventricular ethanol and ethanol intake: A behavioral and radiographic studyPharmacology Biochemistry and Behavior, Vol. 3, No. 3On the specification of taste neurons in the rat tongueBrain Research, Vol. 75, No. 1Interaction of neural systems which control body waterBrain Research, Vol. 49, No. 2Taste phenomena and drug effects on thirst-induced fluid consumption by ratsNeuropharmacology, Vol. 11, No. 2Temperature acclimation in the nervous system of the brown bullhead (Ictalurus nebulosus)Comparative Biochemistry and Physiology Part A: Physiology, Vol. 40, No. 3Taste preference following cross-innervation of rat fungiform taste budsPhysiology & Behavior, Vol. 4, No. 6Combined effects of testosterone and motor, sensory, or gustatory nerve reinnervation on the regeneration of taste budsExperimental Neurology, Vol. 24, No. 2Rôle of nerve and epithelium in the regulation of alkaline phosphatase activity in gustatory papillaeExperimental Neurology, Vol. 23, No. 1Changes in phosphatase enzymes following denervation of the vallate papilla of the ratExperimental Neurology, Vol. 22, No. 1Hypogeusia and taste preference behavior in the ratLife Sciences, Vol. 6, No. 7 More from this issue > Volume 46Issue 2April 1966Pages 173-211 Copyright & PermissionsCopyright © 1966 by American Physiological Societyhttps://doi.org/10.1152/physrev.1966.46.2.173PubMed5325968History Published online 1 April 1966 Published in print 1 April 1966 Metrics

Journal of Comparative NeurologyVolume 111, Issue 2 p. 231-259 Article Cortical and thalamic areas involved in taste discrimination in the albino rat Robert M. Benjamin, Robert M. Benjamin Laboratory of Neurophysiology, Department of Physiology, University of Wisconsin Medical School, Madison, WisconsinSearch for more papers by this authorKonrad Akert, Konrad Akert Laboratory of Neurophysiology, Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin Aided by grants from the National Institute of Neurological Diseases and Blindness, N.I.H., U.S.P.H.S. (B–732), and from the Research Committee of the University of Wisconsin out of funds provided by the Wisconsin Research Foundation.Search for more papers by this author Robert M. Benjamin, Robert M. Benjamin Laboratory of Neurophysiology, Department of Physiology, University of Wisconsin Medical School, Madison, WisconsinSearch for more papers by this authorKonrad Akert, Konrad Akert Laboratory of Neurophysiology, Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin Aided by grants from the National Institute of Neurological Diseases and Blindness, N.I.H., U.S.P.H.S. (B–732), and from the Research Committee of the University of Wisconsin out of funds provided by the Wisconsin Research Foundation.Search for more papers by this author First published: April 1959 https://doi.org/10.1002/cne.901110203Citations: 95 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume111, Issue2April 1959Pages 231-259 RelatedInformation

"The quinine thresholds as measured by the one-bottle, 1-hr. method are significantly higher than the two-bottle, 24-hr. thresholds. Ablation of the cortical receptive area for the IXth and chorda tympani nerves, which increases the two-bottle, 24-hr. thresholds, has no effect on the one-bottle, 1-hr. thresholds." (PsycINFO Database Record (c) 2006 APA, all rights reserved)

ArticlesCORTICAL LOCALIZATION OF TASTE IN ALBINO RATRobert M. Benjamin, and Carl PfaffmannRobert M. Benjamin, and Carl PfaffmannPublished Online:01 Jan 1955https://doi.org/10.1152/jn.1955.18.1.56MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByThalamo-insular pathway conveying orofacial muscle proprioception in the ratNeuroscience, Vol. 365Taste area in granular and dysgranular insular cortices in the rat identified by stimulation of the entire oral cavityNeuroscience Research, Vol. 9, No. 3Partial recovery of gustatory function after neurol tissue transplantation to the lesioned gustatory neocortexBrain Research Bulletin, Vol. 20, No. 5On a neural mechanism for cortical processing of taste quality in the ratBrain Research, Vol. 400, No. 2Blood glucose level affects perceived sweetness intensity in ratsPhysiology & Behavior, Vol. 41, No. 5Gustatory cortex in the rat. I. Physiological properties and cytoarchitectureBrain Research, Vol. 379, No. 2Feeding and tasteProgress in Neurobiology, Vol. 27, No. 4Two distinct projection areas from tongue nerves in the frontal operculum of macaque monkeys as revealed with evoked potential mappingNeuroscience Research, Vol. 2, No. 6Neocortical involvement in the acquisition and retention of learned alcohol aversions in ratsAlcohol, Vol. 2, No. 4Neuropeptides are present in projection neurones at all levels in visceral and taste pathways: from periphery to sensory cortexBrain Research, Vol. 299, No. 2Special senses are really special: Evidence for a reciprocal, bilateral pathway between insular cortex and nucleus parabrachialisBrain Research Bulletin, Vol. 8, No. 5Direct connectivity between pontine taste areas and gustatory neocortex in ratBrain Research, Vol. 234, No. 1Insular cortex projection to the nucleus of the solitary tract and brainstem visceromotor regions in the mouseBrain Research Bulletin, Vol. 8, No. 2Corticofugal effects on the activity of thalamic taste cellsBrain Research, Vol. 193, No. 1Topographical arrangement of thalamic neurons projecting to the orbital gyrus in the catExperimental Neurology, Vol. 67, No. 3Hypothalamic convergence of external and internal stimulation leading to early ingestive and metabolic responsesBrain Research Bulletin, Vol. 5Odorant responses in taste neurons of the rat NTSBrain Research, Vol. 135, No. 2Cortical responses to electrical and gustatory stimuli in the rabbitBrain Research, Vol. 94, No. 3Projections of thalamic gustatory and lingual areas in the ratBrain Research, Vol. 92, No. 1The pontine taste area in the ratBrain Research, Vol. 91, No. 1Cortical-thalamic relationships in the ratExperimental Neurology, Vol. 47, No. 3Cortical and subcortical components of the conditioned saccharin aversionPhysiology & Behavior, Vol. 11, No. 4A solution to the problem of cerebral cortical localization of taste in the catExperimental Neurology, Vol. 37, No. 3Summated cerebral responses to taste stimuli in ratPhysiology & Behavior, Vol. 9, No. 5Involvement of gustatory neocortex in the learning of taste aversionsPhysiology & Behavior, Vol. 9, No. 4Thalamocortical relations in gustationBrain Research, Vol. 36, No. 2Cortical representation of the ipsilateral chorda tympani nerve in the catBrain Research, Vol. 16, No. 2Projection of taste nerve afferents to anterior opercular- insular cortex in squirrel monkey (Saimiri sciureus)Brain Research, Vol. 7, No. 2 More from this issue > Volume 18Issue 1January 1955Pages 56-64 https://doi.org/10.1152/jn.1955.18.1.56PubMed13222157History Published online 1 January 1955 Published in print 1 January 1955 Metrics

[This corrects the article DOI: 10.1016/j.heliyon.2022.e10890.].