Corticothalamic Connections Research Articles

Corticothalamic connections of paralimbic regions in the rhesus monkey.

This study addressed the issue of whether paralimbic regions of the cerebral cortex share common thalamic projections. The corticothalamic connections of the paralimbic regions of the orbital frontal, medial prefrontal, cingulate, parahippocampal, and temporal polar cortices were studied with the autoradiographic method in the rhesus monkey. The results revealed that the orbital frontal, medial prefrontal, and temporal polar proisocortices have substantial projections to both the dorsomedial and medial pulvinar nuclei, whereas the anterior cingulate proisocortex (area 24) projects exclusively to the dorsomedial nucleus. These proisocortical areas also have thalamic connections with the intralaminar and midline nuclei. The cortical areas between the proisocortical regions on the one hand and the isocortical areas on the other, that is, the posterior cingulate region (area 23) and the posterior parahippocampal gyrus (areas TF and TH), project predominantly to the dorsal portion of the medial pulvinar nucleus, the anterior nuclear group (AV, AM), and the lateral dorsal (LD) nucleus. Additionally, the posterior cingulate and medial parahippocampal gyri (area TH) have projections to the lateral posterior (LP) nucleus. Thus, it appears that the proisocortical areas, which are characterized by a predominance of infragranular layers and an absence of layer IV, have common thalamic relationships. Likewise, the intermediate paralimbic areas between the proisocortex and isocortical regions, which also have a predominance of infragranular layers but in addition have evidence of a fourth layer, project to the medial pulvinar and to the so-called limbic nuclei, AV, AM, LD, as well as a modality-specific nucleus, LP.

Chapter 26: Some extra-striate corticothalamic connections in macaque monkeys

This chapter describes some corticothalamic connections of the middle temporal (MT) area and the neighbouring, MT-recipient, visual region situated in the fundus and upper bank of superior temporal sulcus (STS) of the macaque monkey. These connections turned out to be part of a parallel network reciprocally linking sensory structures to cortical and subcortical formations that, from anatomical and electrophysiological investigations, appear to be involved in the neural control of directionally oriented eye movements, as well as in the orientation of visual attention. In the macaque monkey, the caudal half of the STS is an important cortical station of the extrageniculo-striate visual system in which discrete visual areas have been identified. Among these, the MT area is reputed to play a key role in visual motion analysis because of the property of its neurons to selectively respond to the direction and speed of moving visual stimuli. Areas surrounding MT are less defined as to their anatomical limits, connections, and functions. The pieces of evidence highlighted in this chapter suggest that the extrageniculo-striate corticothalamic system involving the superior temporal cortex is an intimate part of a complex network of functional units.

Patterns of reciprocity in auditory thalamocortical and corticothalamic connections: study with horseradish peroxidase and autoradiographic methods in the rat medial geniculate body.

The patterns of reciprocity between retrogradely labeled thalamocortical cells of origin and anterogradely projecting corticothalamic axon terminals were studied in the subdivisions of the adult rat medial geniculate body following auditory cortical injections of mixtures of horseradish peroxidase and [3H]leucine. The labeling produced by each method was examined independently, both qualitatively and quantitatively, in adjacent series of tetramethylbenzidine-processed sections and in autoradiographs after 24-96 hour survivals. The distribution and number of labeled cells and axon terminals were assessed separately for each method and compared systematically throughout the rostro-caudal extent of the medial geniculate complex. The principal finding was that zones containing many retrogradely labeled neuronal somata are not completely coextensive with areas of heavy terminal labeling within the medial geniculate body, although there is a gross congruence of thalamocortical-corticothalamic projections. Conversely, we found many zones of autoradiographic silver grains without retrogradely labeled somata in the adjacent sections; in general, the autoradiographic zones of non-reciprocity were more extensive and marked than were retrograde zones of non-reciprocity. The rat medial geniculate complex could be subdivided on the basis of its neuronal organization, cytoarchitecture, fiber architecture, and thalamocortical and corticothalamic connections into three major parts: the ventral, dorsal, and medial divisions. This pattern of organization was comparable, though not identical, to that of the corresponding subdivisions in the cat medial geniculate body (Winer: Adv. Anat. Embryol. Cell Biol. 86:1-98, '85). While the retrograde labeling appeared to mark many of the different types of neurons in each of the three divisions, there were distinct local and quantitative and qualitative differences in the distribution of autoradiographic terminal labeling. The ventral division received the heaviest cortical input, the medial division the least labeling, while the dorsal division was intermediate. Thus, corticogeniculate projections to the ventral division often produced values 20-100 times above background (absolute values: 2,001-10,000 silver grains/14,400 micron2; background: less than 100 silver grains/14,400 micron2); the same projection to the dorsal division usually resulted in grain counts no more than 5-20 times above background (501-2,000/14,400 micron2), while in the medial division the number of silver grains rarely exceeded two to five times the background (201-500/14,400 micron2).(ABSTRACT TRUNCATED AT 400 WORDS)

Corticothalamic connections of the posterior parietal cortex in the rhesus monkey.

Corticothalamic connections of posterior parietal regions were studied in the rhesus monkey by using the autoradiographic technique. Our observations indicate that the rostral superior parietal lobule (SPL) is connected with the ventroposterolateral (VPL) thalamic nucleus. In addition, whereas the rostral SPL is connected with the ventrolateral (VL) and lateral posterior (LP) thalamic nuclei, the rostral IPL has connections with the ventroposteroinferior (VPI), ventroposteromedial parvicellular (VPMpc), and suprageniculate (SG) nuclei as well as the VL nucleus. The caudal SPL and the midportion of IPL show projections mainly to the lateral posterior (LP) and oral pulvinar (PO) nuclei, respectively. These areas also have minor projections to the medial pulvinar (PM) nucleus. Finally, the medial SPL and the caudal IPL project heavily to the PM nucleus, dorsally and ventrally, respectively. In addition, the medial SPL has some connections with the LP nucleus, whereas the caudal IPL has projections to the lateral dorsal (LD) nucleus. Furthermore, the caudal and medial SPL and the caudal IPL regions have additional projections to the reticular and intralaminar nuclei-the caudal SPL predominantly to the reticular, and the caudal IPL mainly to the intralaminar nuclei. These results indicate that the rostral-to-caudal flow of cortical connectivity within the superior and inferior parietal lobules is paralleled by a rostral-to-caudal progression of thalamic connectivity. That is, rostral parietal association cortices project primarily to modality-specific thalamic nuclei, whereas more caudal regions project most strongly to associative thalamic nuclei.

Corticothalamic connections from the second somatosensory area and neighboring regions in the lateral sulcus of macaque monkeys

Corticothalamic connections were shown between the second somatosensory area in primates and the ventroposterior nuclei of the thalamus. These projections were topographically arranged with those from the hindlimb portions of SII traced to the most lateral and posterior parts of the ventroposterior lateral nucleus (VPLc) and those from the forelimb located medially within VPLc. The densest labeling was found ventrally in VPLc and dorsally within ventroposterior inferior n. (VPI) only after injections of the forelimb. A more scattered, dorsal distribution of labeling was seen in the rest of VPLc from injections involving more proximal parts of the body representation in SII.

Connections between the thalamus and the somatosensory areas of the anterior ectosylvian gyrus in the cat

The thalamocortical and corticothalamic connections of the second somatic sensory area (SII) and adjacent cortical areas in the cat were studied with anterograde and retrograde tracers. Injections consisted of horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA) or a mixture of equal parts of tritiated leucine and proline. The cortical regions to be injected were electrophysiologically studied with microelectrodes to determine the localization of the selected components of the body representation in SII. The distribution of recording points was correlated in each case with the extent of the injection mass in the cortex. Distributions of retrograde and anterograde labeling in the thalamus were reconstructed from serial coronal sections. The results from cases with injections of tracers exclusively confined to separate parts of the body map in SII indicated a fairly precise topographical organization of projections from the ventrobasal complex (VB) to SII. The labeled cells and fibers were located within a series of lamella-like rods that curved throughout the dorsoventral and rostrocaudal axis of VB. The position and extent of these lamellae shifted from medial and ventral, in the medial subdivision of ventral posterior lateral nucleus (VPLm) for radial forelimb digit zones of SII, to dorsal, posterior, and lateral, in the lateral subdivision of ventral posterior lateral nucleus (VPL1) for proximal leg and trunk regions in SII. For every injected area in SII the densest clustering of labeled cells and fibers was usually more posteriorly represented in VB. The distribution in these dense zones of labeling often extended through the central core of VB. SII projecting neurons were also consistently noted in the extreme rostral portion of the medial subdivision of the posterior nuclei (Pom) that lies dorsal to VB. Corticothalamic and thalamocortical connections for SII were entirely reciprocal. Injections of tracers into cortical areas surrounding SII labeled other parts of the posterior complex but failed to label any part of VB except when the injection mass also diffused into SII. Injections into the somatic sensory cortex located lateral to SII, within the lips and depth of the upper bank of the anterior ectosylvian sulcus (AES), heavily labeled the central and posterior portions of Pom. Substantial labeling was noted in the lateral (Pol) and intermediate (Poi) divisions of Po only when the injections involved some part of the auditory areas located immediately posterior to SII. This region included the anterior auditory area that occupies the most posterior part of the AEG and both banks of the immediately adjoining AES. The magnocellular nucleus of the medial geniculate (MGmc) was labeled only when some part of the auditory cortex was injected. The suprageniculate nucleus (SG) was labeled from the insula and lower bank of the AES. These results indicated that the medial (rostral and caudal Pom) and lateral components (Poi, Pol, MGmc) of the posterior complex have separate cortical projection zones to somatic sensory and auditory cortical regions, respectively. SIV and the lateral extent of area 5a located in the medial bank of the anterior suprasylvian sulcus sent projections to the deep layers of the superior colliculus and the ventrolateral periaqueductal gray. No cortico-tectal projections were seen from SII.

Participation of corticothalamic cells in penicillin-induced generalized spike and wave discharges

Single unit extracellular recordings were performed in the cortex of awake painlessly immobilized unanesthetized cats during generalized spike and wave discharges (SW) induced by i.m. penicillin. Corticothalamic cells were identified in cortical areas 3a and 4γ by stimulating n. ventralis lateralis (VL) and in cortical areas 5 and 7 by stimulating n. lateralis posterior (LP). Twelve of 24 neurons antidromically invaded from VL were also pyramidal tract cells. Two of 11 neurons antidromically invaded from LP also displayed orthodromic responses. Corticothalamic cells fired bursts of action potentials in association with the ‘spike’ whereas a period of inhibition was associated with the ‘wave’ of the SW complex. The data suggest that in this experimental model the appearance of SW in the thalamus is due to secondary activation of thalamic neurons by volleys arising from the cortex and mediated through corticothalamic connections.

The effect of mirthfulness upon amount of discordant right-left occipital EEG alpha

A total of 68 subjects participated in two experiments that tested the effect of exposure to comedy upon amount of discordant right-left occipital EEG alpha. Data from both showed less discordant alpha in the “laughers” and more in the “nonlaughers” at the end of exposure to a filmed comedy, as contrasted by no such group difference before treatment. Experiment 2 clarified that the production of discordant alpha in the right hemisphere was significant to this group difference, that this effect was specific to comedy treatment (nondiscriminative effects of exposure to a neutral film), and that a reversed group difference in amount of discordant right hemisphere alpha occurred after instructed hypoventilation (nondiscriminative effect of hyperventilation; counterbalanced order of all four treatments). The results were discussed in relation to (a) recent findings on right-left hemisphere characteristics of depressed individuals, (b) the significance of motivational states, (c) a link between cerebral blood flow and EEG indicators of activation, (d) ventilatory effects upon cortical activation, (e) personality differences inherent in tolerance for CO2-blood concentration, and (f) recent findings on corticothalamic connections.

The thalamocortical and corticothalamic connections of AI, AII, and the anterior auditory field (AAF) in the cat: evidence for two largely segregated systems of connections.

AbstractThe thalamocortical and corticothalamic connections of the three cortical auditory fields—first (AI), second (AII), and anterior (AAF)—were defined using anterograde and retrograde tracing techniques. Microinjections of tracers were placed at one or two different physiologically identified loci after these fields had been mapped using microelectrode recording techniques. This approach ensured that the injections were well within the borders of each field that was studied. By making injections at different positions in the cochleotopic representations in A1 and AAF the systematic topographies of the connections between these cortical fields and the medial geniculate body subdivisions were determined.The thalamocortical and corticothalamic reciprocal projections of single loci in AI were from and to single columns passing rostrocaudally through the deep dorsal nucleus (Dd) and medial division (M) of the medial geniculate body (MGB) and from and to folded sheets of labelled neurons passing rostrocaudally through pars lateralis (VI) and pars ovoidea (Vo) of the ventral division. The connections of AI with VI and Vo were very strong. There were also thalamocortical and corticothalamic connections between the lateral division of the posterior group of thalamus (Pol) and single loci in AI.The thalamocortical and corticothalamic reciprocal connections of AAF with the auditory thalamus were similar to the A1 connections with the exception that the connections with the ventral division of the MGB were relatively weaker and, in the case of the thalamocortical projection, more discontinuous.AII loci are thalamocortically and corticothalamically connected with the caudal dorsal nucleus (Dc), the ventral lateral nucleus (VL), and the medial division (M).The topography of all connections of AAF and A1 with the MGB varied systematically and was consistent with a cochleotopic organization of connections between the MGB and the two cortical fields.Since the thalamocortical and corticothalamic connections of these three cortical fields are reciprocal, we were able to compare directly their connections in individual cats by introducing anterograde tracer in one field and retrograde tracer in another. While AI and AAF were connected to the same subdivisions of the MGB and had the same systematic topography of connections, the connections of AII and AI (or AAF) were largely segregated (with the only overlap occurring in M). Results of injections introduced into other cortical fields in this study and the results of previous studies by other investigators (Rose and Woolsey, '58; Graybiel, '73; Casseday et al., '76; Winer et al., '77) are consistent with the interpretation that there are two largely segregated connectional systems between the auditory thalamus and cortex: a “cochleotopic system” that includes AI and AAF and a “diffuse system” that includes AII.Small injections of anterograde tracers at higher‐frequency representational sites in AI or AAF, or of retrograde tracer in AI, produced a discontinuous, periodic pattern of dense and light labelling in VI. Reconstructions showed that these discontinuities of label, in three dimensions, formed parallel columns oriented rostrocaudally.

Unitary responses of the hypothalamic nuclei to stimulation of the frontobasal neocortex

Unitary responses in the hypothalamic nuclei to stimulation of the frontobasal zones of the cortex (proreal, orbito-insular, and basal temporal regions) were studied. Cortico-thalamic connections were found to possess definite topical organization: the orbito-frontal zones of the cortex have a more marked effect on unit activity of the hypothalamic nuclei than the basal temporal cortex. Antidromic activation, during stimulation of a particular region of the cortex, of neurons excited orthodromically by stimulation of another cortical structure, enables a number of neuronal circuits functioning within the forebrain to be distinguished. The first circuit includes the orbital gyrus, preoptic zone, and proreal gyrus. The second circuit has the same cortical components as the first, but its relay in the hypothalamus takes place in the region of the mamillary bodies. The third circuit is represented by the basal temporal cortex, lateral hypothalamus, and prefrontal cortex.

Thalamic projections of somatosensory cortical areas

The results of morphological investigations of degenerated fibers show that the first somatosensory cortical area is connected by descending cortico-thalamic fibers with the posterior ventral nucleus of the thalamus. The second somatosensory area is connected simultaneously with the caudal part of the posterior ventral nucleus and with the posterior group of thalamic nuclei. These cortico-thalamic connections are distributed on a somatotopic principle.

Corticothalamic connections of suprasylvian cortex in monkey

Cortical lesions were made along the superior border of the sylvian fissure in 11 squirrel and four macaque monkeys. The course of degenerating fibers in the thalamus was determined by utilizing the Nauta and Fink-Heimer I techniques. The principal projection sites of suprasylvian cortex were found to be the nuclei ventralis posterior medialis, ventralis posterior lateralis, ventralis posterior inferior, pulvinaris oralis, and pulvinaris medialis. Lesser amounts of terminal degeneration occurred in the nuclei reticularis, ventralis lateralis, lateralis posterior, the intralaminar nuclei, and the posterior and pretectal areas of the thalamus. The connections of the suprasylvian cortex that corresponds to somatosensory area II with a phylogenetically new thalamic nucleus, the pulvinaris oralis, suggests a specialization of SII functions in the monkey.

An anatomical study of the efferent connections of the thalamic reticular nucleus.

A neuro-anatomical investigation into the thalamic reticular nucleus and its connections was made in the albino rat, using the method of retrograde degeneration and the Nauta-Gygax method. The results correspond to the description given by Scheibel and Scheibel and indicate connections of the neurons of the reticular which the principal thalamic nuclei and the rostral part of the intralaminar thalamic nuclei. A topographical arrangement of the efferent connections of the reticular nucleus is demonstrated. The projection of the reticular nucleus upon the thalamus duplicates the cortico-thalamic connections.

The corticothalamic projection from the pericruciate and coronal gyri in the cat. An experimental study with silver-impregnation methods

The corticothalamic projections from the pericruciate and coronal gyri in adult cats have been studied with the silver-impregnation method of Nauta. The efferent fibers from these cortical areas follow three different routes before they reach their area of termination in the ipsilateral thalamus. The majority of corticothalamic fibers course in nucleus reticularis thalami (R) and the external medullary lamina and enter different thalamic nuclei at successively caudal levels. Other corticofugal fibers leave the internal capsule at rostral levels, pierce R and course through various rostral thalamic nuclei before they terminate at more caudal diencephalic levels. By a third and more circuitous route, fibers leave the cerebral peduncle at the meso-diencephalic junction and course in a dorsorostral direction towards posteroinferior and medial thalamic structures. The postcruciate gyrus sends fibers to the following thalamic nuclei: reticularis (R), ventralis lateralis (VL), ventralis posterolateralis (VPL), posterior group (PO), centrum medianum (CM), parafascicularis (Pf) and paracentralis (Pc). In addition to the above-mentioned nuclei, the precruciate gyrus projects to ventralis anterior (VA), ventralis medialis (VM) and the lateral part of caudal medialis dorsalis (MD). The coronal gyrus projects upon R, VA, VL, PO, CM, Pf, Pc, lateral part of caudal MD, centralis lateralis (CL), ventralis posteromedialis (VPM), the parvocellular part of VPM (VPMpc) and ventralis posteroinferior (VPI). Fibers from medial and lateral parts of the pericruciate gyri end in lateral and medial regions, respectively, of VPL. Fibers from the coronal gyrus end in VPM. This topographical organization of the corticothalamic fibers is also seen to a minor extent in R, VL and PO. Most efferent fibers to VL from the precruciate gyrus, however, project diffusely upon a zone which extends throughout the rostrocaudal extent of VL medial to the VB complex. Many corticofugal fibers to VL and the VB complex from the pericruciate and coronal gyri are of thick caliber, those to the former nucleus being on an average somewhat thinner than those to the latter. The fibers to CM, Pf, Pc and MD are quite thin. The problem of retrograde fiber degeneration in thalamocortical axons following cortical lesions is discussed. The advantages and limitations of the Nauta method have been discussed in light of recent electron microscope studies on degeneration processes in the nervous system. The importance of varying the survival time in experimental degeneration studies is emphasized. The findings are finally discussed in the context of earlier reports with respect to the anatomy and physiology of corticothalamic connections.

A re-evaluation of the cytoarchitecture of the ventral nuclear complex of the cat's thalamus on the basis of corticothalamic connections

Summary A short description has been given of the thalamic nuclei which receive afferent connections from the frontal cerebral cortex and the first and second somatic sensory cortical areas in the cat. The findings reported correspond largely to previous observations on the topography of the thalamus. However, studies on corticothalamic connections have proved to be of value in delimiting some thalamic structures more accurately. The areas of termination of corticothalamic fibres in VPM and VPL from face and limb areas, respectively, of the cerebral cortex are separated by a thick myelinated fibre bundle. Furthermore, a thin fibre bundle separates the 2 parts of VPL which receive afferent fibres from hind- and forelimb areas of the sensorimotor cortical areas. Marked differences in cytoarchitecture help to separate VPMpc and VPI from VPM. However, these nuclei appear to receive afferent connections from largely identical cortical areas. The posterior group of nuclei (PO) is distinct from the ventral group by differences in cytoarchitecture and particulars in the corticothalamic connections. In PO are included the caudal end of VPL1, rostral MGmc and ventral part of caudal LP. It is emphasized that a profound knowledge of fibre connections combined with the use of other methods such as the Golgi technique, histochemistry and electron microscopy, is needed in order to obtain a complete and rational comprehension of thalamic topography.

Corticothalamic connections in the projection system of the pelvic nerve

Corticothalamic connections in the projection system of the pelvic nerve

Cortico-thalamic connections in the cat as revealed by "physiological neuronography".

Cortico-thalamic connections in the cat as revealed by "physiological neuronography".