Cerebral areas mediating visual redirection of gaze: cooling deactivation of 15 loci in the cat

In humans, damage to posterior parietal or frontal cortices often induces a severe impairment of the ability to redirect gaze to visual targets introduced into the contralateral field. In cats, unilateral deactivation of the posterior middle suprasylvian (pMS) sulcus in the posterior inferior parietal region also results in an equally severe impairment of visually mediated redirection of gaze. In this study we tested the contributions of the pMS cortex and 14 other cortical regions in mediating redirection of gaze to visual targets in 31 adult cats. Unilateral cooling deactivation of three adjacent regions along the posterior bend of the suprasylvian sulcus (posterior middle suprasylvian sulcus, posterior suprasylvian sulcus, and dorsal posterior ectosylvian gyrus at the confluence of the occipital, parietal, and temporal cortices) eliminated visually mediated redirection of gaze towards stimuli introduced into the contralateral hemifield, while the redirection of gaze toward the ipsilateral hemifield remained highly proficient. Additional cortical loci critical for visually mediated redirection of gaze include the anterior suprasylvian gyrus (lateral area 5, anterior inferior parietal cortex) and medial area 6 in the frontal region. Cooling deactivation of: 1) dorsal or 2) ventral posterior suprasylvian gyrus; 3) ventral posterior ectosylvian gyrus, 4) middle ectosylvian gyrus; 5) anterior or 6) posterior middle suprasylvian gyrus (area 7); 7) anterior middle suprasylvian sulcus; 8) medial area 5; 9) the visual portion of the anterior ectosylvian sulcus (AES); 10) or lateral area 6 were all without impact on the ability to redirect gaze. In summary, we identified a prominent field of cortex at the junction of the temporo-occipito-parietal cortices (regions pMS, dPE, PS), an anterior inferior parietal field (region 5L), and a frontal field (region 6M) that all contribute critically to the ability to redirect gaze to novel stimuli introduced into the visual field during fixation. These loci have several features in common with cortical fields in monkey and human brains that contribute to the visually guided redirection of the head and eyes.     

Thalamocortical connections of the rostral intralaminar nuclei: an autoradiographic analysis in the cat

In this study the pattern of projections from the rostral intralaminar thalamic nuclei to the cerebral cortex was examined in the cat by autoradiography. Injections of tritiated proline and leucine were placed into the central lateral, paracentral, central medial, and para-stria medullaris nuclei. After injections into the central lateral nucleus, label is present on the lateral side within the presylvian sulcus, in most of the suprasylvian gyrus, including the adjacent lateral and suprasylvian sulci, and in the posterior corner of the ectosylvian gyrus. On the medial side, label is present in the orbitofrontal (Of), precentral agranular (Prag), anterior limbic (La), retrosplenial (Rs), and postsubicular (Ps) areas, as defined by Rose and Woolsey ('48a). The cingulate gyrus also contains label throughout (part of which was defined as the "cingular area," Cg, by Rose and Woolsey, '48a). Label is also found on both banks of the splenial and cruciate sulci. In addition, label is present within the lateral gyrus, on both its lateral and medial sides. The paracentral projections are similar to the central lateral input. On the lateral side, label is found within the presylvian sulcus, suprasylvian gyrus and adjacent lateral and suprasylvian sulci, and posterior ectosylvian gyrus. Medially, label is present in the Of, Prag, La, Cg, Rs, and Ps areas, and within the cruciate and splenial sulci, and in portions of the lateral gyrus. Following injections of the central medial nucleus, label is present in the presylvian sulcus; but in contrast to the central lateral and paracentral projections, the suprasylvian gyrus is labeled only in its posterior part. The central medial nucleus also projects to the posterior lateral gyrus, both laterally and medially. Also, the central medial nucleus projects heavily to rostral cortical zones, which include the Of, Prag and La areas, cruciate sulcus, and the rostral cingulate gyrus. The para-stria medullaris nucleus projects only to the presylvian sulcus and orbitofrontal cortex laterally, but, medially, has an extensive input similar to the central lateral and paracentral projections in that label is present in the Of, Prag, La, Cg, Rs, and Ps areas, in the cruciate and splenial sulci, and in the posterior lateral gyrus. The laminar distribution of label is as follows: the central lateral, paracentral and para-stria medullaris nuclei project primarily to layers I and III, whereas the central medial nucleus projects to layers I and VI. In addition, the central lateral projection has a patchy appearance in the retrosplenial and postsubicular cortices.     

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 (VPLl) 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 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 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 supe- rior colliculus and the ventrolateral periaqueductal gray. No cortico-tectal projections were seen from SII.     

Visual and auditory association areas of the cat's posterior ectosylvian gyrus: thalamic afferents

The feline posterior ectosylvian gyrus contains a broad band of association cortex that is bounded anteriorly by tonotopic auditory areas and posteriorly by retinotopic visual areas. To characterize the possible functions of this cortex and to throw light on its pattern of internal divisions, we have carried out an analysis of its thalamic afferents. Deposits of differentiable retrograde tracers were placed at 17 cortical sites in nine cats. The deposit sites spanned the crown of the posterior ectosylvian gyrus and adjacent cortex in the suprasylvian sulcus. We compiled counts of retrogradely labeled neurons in 12 thalamic nuclei delineated by use of Nissl and acetylcholinesterase stains. We then employed a statistical clustering algorithm to identify groups of injections that gave rise to similar patterns of thalamic labeling. The results suggest that the posterior ectosylvian gyrus contains 3 fundamentally different cortical districts that have the form of parallel vertical bands. Very anterior cortex, overlapping previously identified tonotopic auditory areas (AI, P and VP) receives a dense projection from the laminated division of the medial geniculate body (MGl). An intermediate strip, to which we refer as the auditory belt, is innervated by axons from nontonotopic divisions of the medial geniculate body (MGds, MGvl, MGm, and MGd), from the lateral division of the posterior group (Pol), and from the posterior suprageniculate nucleus (SGp). A posterior strip, to which we refer as EPp, receives strong projections from the LM-SG complex (LM-SGa and LMp), and lighter projections from the intralaminar and lateroposterior (LPm and LPl) nuclei. On grounds of thalamic connectivity, EPp is not obviously distinguishable from adjacent retinotopic visual areas (PLLS, DLS, and VLS), and may be regarded as forming, together with these areas, a connectionally homogeneous visual belt.     

Ectosylvian visual area of the cat: location, retinotopic organization, and connections

We have mapped out the ectosylvian visual area (EVA) of the cat in a series of single- and multiunit recording studies. EVA occupies 10-20 mm2 of cortex at the posterior end of the horizontal limb of the anterior ectosylvian sulcus. EVA borders on somatosensory cortex anteriorly, auditory cortex posteriorly, and nonresponsive cortex laterally. EVA exhibits limited retinotopic organization, as indicated by the fact that receptive fields shift gradually with tangential travel of the microelectrode through cortex. However, a point-to-point representation of the complete visual hemifield is not present. We have characterized the afferent and efferent connections of EVA by placing retrograde and anterograde tracer deposits in EVA and in other cortical visual areas. The strongest transcortical fiber projection to EVA arises in the lateral suprasylvian visual areas. Area 20, the granular insula, and perirhinal cortex provide additional sparse afferents. The projection from lateral suprasylvian cortex to EVA arises predominantly in layer 3 and terminates in layer 4. EVA projects reciprocally to all cortical areas from which it receives input. The projection from EVA to the lateral suprasylvian areas arises predominantly in layers 5 and 6 and terminates in layer 1. EVA is linked reciprocally to a thalamic zone encompassing the lateromedial-suprageniculate complex and the adjacent medial subdivision of the latero-posterior nucleus. We conclude that EVA is an exclusively visual area confined to the anterior ectosylvian sulcus and bounded by nonvisual cortex. EVA is distinguished from other visual areas by its physical isolation from those areas, by its lack of consistent global retinotopic organization, and by its placement at the end of a chain of areas through which information flows outward from the primary visual cortex.     

Divergence and collateral axon branching in subsystems of visual cortical projections from the cat lateral posterior nucleus.

The projections from the lateral (LPl), intermediate (LPi) and medial (LPm) subdivisions of the cat lateral posterior nucleus (n. LP) to visual areas 17, the posteomedial (PMLS) and posterolateral (PLLS) lateral suprasylvian and anterior ectosylvian (AEV) were studied using the retrograde labeling technique following concomitant injections of fluorescent dyes (Fast blue, Nuclear yellow, Evans blue and Rhodamine beta-isothiocyanate) into the different cortical loci. The results showed a medial-lateral topographical reversal of the visual n. LP-cortical connections: The ventral portion of LPl projects to area 17 whereas more dorsolateral regions of LPl and lateral LPi provide input to PMLS. Cells in medial LPi project mainly to the PLLS cortex and AEV receives afferents from the LPm. Areas of overlap were identified within the ventral LPl which projects to both area 17 and PMLS and within the LPi/LPm border region at the origin of connections to both PLLS and AEV. Furthermore, some single neurons within the areas of overlap were found to be double-labeled indicating divergent projections to their respective cortical targets via collateral axon branching. The data show that divergence and axonal branching are common features of the different n.LP-visual cortical subsystems and support the notion of the existence of families of thalamo-cortical systems which are distinct in their connection patterns and underlying functional properties.     

Topographical linkage of tecto-thalamo-anterior ectosylvian sulcal cortex in the cat: an 125I-WGA autoradiographic study

Following injection of 125I-WGA into various parts of the caudal thalamus in the cat, the distribution of orthograde and retrograde labels in the cortex around the anterior ectosylvian sulcus (AESS) and the superior colliculus (SC) was examined autoradiographically. When 125I-WGA injections involved the medial part of nucleus lateralis posterior (Lp) of the thalamus, both orthograde and retrograde labels consistently appeared in the cortex around AESS, and retrograde labels in the SC. The topographical organization of the cortical connections with the medial part of Lp can be well correlated with that of the tecto-thalamic projections, in such a way that the dorsal portion of the medial part of Lp which receives fibers from the rostromedial part of SC is connected reciprocally with the lateral lip of AESS and the crown of the anterior sylvian gyrus; whereas, the most ventral portion of the medial part of Lp which receives tectal afferents from the caudolateral part of SC is connected with the dorsal bank and fundus of AESS. These results suggest the existence of retinotopically ordered linkage between the tecto-Lp and the Lp-AESS connections in the cat.     

The lateral suprasylvian corticotectal projection in cats

The projection from the lateral suprasylvian visual areas to the superior colliculus was investigated in cats using both anterograde and retrograde tracing techniques. The retrograde transport of horseradish peroxidase (HRP) or wheat germ agglutinin-HRP (WGA-HRP) from their site of deposit in the superior colliculus indicates that all divisions of the lateral suprasylvian visual areas project to both the superficial and deep layers of the superior colliculus. However, following tracer deposits in the superior colliculus that are confined to the layers below the stratum opticum (deep layers), more neurons are labeled along the lateral bank than along the medial bank of the middle suprasylvian sulcus. Conversely, tracer deposits in the superior colliculus dorsal to and including the stratum opticum label more cells in the medial than the lateral bank. These retrograde experiments also confirm that the visual cortex along the lateral gyrus (areas 17 and 18) projects to the superficial, but apparently not to the deep layers. The visual area in the cortex surrounding the caudal two-thirds of the anterior ectosylvian sulcus projects to the deep, but not to the superficial layers. The laminar and areal patterns of anterograde axon labeling in the superior colliculus were examined after single deposits of 3H-amino acids (autoradiography), HRP, or WGA-HRP in the lateral suprasylvian cortical regions, or combined isotope and WGA-HRP deposits. Axon labeling in the superior colliculus is generally densest in the stratum opticum and extends either dorsally into the superficial layers or ventrally into the intermediate gray layer. Specifically, the anterior divisions of the lateral suprasylvian cortex project primarily to the lateral portion of the superior colliculus, with the projection from the medial bank biased toward the superficial layers and axons from the lateral bank aimed mainly at the intermediate gray layer with some axons even reaching the deepest gray layer of the superior colliculus. Both the posteromedial and posterolateral divisions of the lateral suprasylvian cortex project to more extensive portions of the mediolateral and rostrocaudal dimensions of the superior colliculus than the anterior divisions. However, the posterolateral division projects more heavily to the intermediate gray layer than the posteromedial division; from the latter, axons distribute more superficially in the superior colliculus. Finally, the cortex surrounding the posterior suprasylvian sulcus projects primarily to the medial part of the superficial layers of the superior colliculus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cortical and subcortical afferent connections of a posterior division of feline area 7 (area 7p)

Area 7 of the cat, as identified cytoarchitecturally, includes cortex both on the middle suprasylvian gyrus and on the anterior lateral gyrus. The aim of the experiments reported here was to determine whether within this zone there are subdivisions with qualitatively different patterns of afferent connectivity. Deposits of distinguishable retrograde tracers were placed at 29 sites in and around area 7 of 15 cats; cortical and subcortical telencephalic structures were then scanned for retrograde labeling. Our results indicate that cortex on the anterior lateral gyrus, although often included in area 7, is indistinguishable on connectional grounds from adjacent somesthetic cortex (area 5b). Cortex with strong links to visual, oculomotor, and association areas is confined to the middle suprasylvian gyrus and the adjacent lateral bank of the lateral sulcus. We refer to this discrete, connectionally defined zone as posterior area 7 (area 7p). Area 7p receives input from visual areas 19, 20a, 20b, 21a, 21b, AMLS, ALLS, and PLLS; from frontal oculomotor cortex (areas 6m and 6l); and from cortical association areas (posterior cingulate cortex, the granular insula, the posterior ectosylvian gyrus, and posterior area 35). Thalamic projections to area 7p arise from three specific nuclei (pulvinar; nucleus lateralis intermedius, pars caudalis; nucleus ventralis anterior) and from the intralaminar complex (nuclei centralis lateralis, paracentralis and centralis medialis). Neurons in a division of the claustrum immediately beneath the somatosensory and visual zones project to area 7p. Within area 7p, anterior-posterior regional differentiation is present, as indicated by the spatial ordering of projections from cingulate and frontal cortex, the thalamus, and the claustrum. Area 7p, as delineated by connectional analysis in this study, resembles cortex of the primate inferior parietal lobule both in its location relative to other cortical districts and in its pattern of neural connectivity.     

Cortical and thalamic afferent connections of the insular and adjacent cortex of the cat

The thalamo-cortical and cortico-cortical afferents of the cat's insular cortex were investigated with the retrograde horseradish peroxidase technique. The most prominent loci of thalamic labeling were the suprageniculate nucleus and parts of the posterolateral nucleus. Injections into the anterior part of the insular cortex also resulted in labeled cells in the ventromedial posterior nucleus and in the intralaminar nuclei, while injections into posterior parts revealed projections from the medial and dorsal parts of the medial geniculate nucleus. Only the anterior and most ventral parts of the insular cortex overlying the anterior rhinal sulcus were connected with the mediodorsal nucleus of the thalamus. All injections into the gyrus sylvius anterior showed a specific pattern of cortical afferents: With the exception of the labeling in the prefrontal cortex and the inferotemporal region, the labeled cells were very narrowly restricted to the presylvian, the suprasylvian, and the splenial sulcus. The thalamic neurons projecting to the cortex were generally organized in a bandlike pattern which crossed nuclear borders. The majority of the cortico-cortical connections originated from sulcal areas next to the prefrontal, parietal, and cingulate cortex, that is, next to so-called association cortices. In the light of the present results the role of the insular cortex as a multifunctional association area is discussed, as well as its relation to other cortical centers.     

Thalamo-cortical organization of the visual system in the cat

Thalamo-cortical relationships in the visual system of the cat were studied by the method of retrograde degeneration. Localized lesions limited to area 17 result in degeneration only in the dorsolateral geniculate body; cell changes are marked in 3 laminae (A, A₁, B), mild in nucleus interlaminaris centralis and minimal in nucleus interlaminaris medialis. Lesions limited to areas 18 and 19 are followed by marked degeneration in the medial interlaminar nucleus, mild in the other laminae; in addition, the lateral part of the posterior thalamic nucleus (ventral or inferior pulvinar) is also atrophied. Following large striate lesions which marginally involved areas 18 and 19, there is also mild, localozed degeneration in the anteroventral and reticular thalamic nuclei. Whin cortical lesions are limited to the convexity of the suprasylvian gyri, degeneration is present in the lateral aspect of laminae A, A₁, B and nucleus interlaminaris centralis and in the medial part of the posterior nucleus, in addition to lateral dorsal, lateral posterior and pulvinar nuclei. Lesions in the ectosylvian gyri result in slight but definite degeneration in the lateral part of lamina A of the dorsal lateral geniculate, but nothing in the posterior nucleus. The geniculate projections to areas 17, 18 and 19, to the suprasylvian and ectosylvian gyri all show a rostrocaudal organization. The geniculostriate projection is also topographically organized in a mediolateral manner. Thus, the geniculocortical projection in the cat is not striate specific but spreads over the occipito-temporal cortex at least as far as the acoustic areas of the ectosylvian gyri. In this species the dorsal lateral geniculate body is not a unitary structure but is a complex of nuclei, all of which receive retinal fibers, and the cortical projections of which overlap those of the posterior, lateral dorsal, lateral posterior, pulvinar, medial geniculate, reticular and anterior thalamic nuclei.     

Distribution and size of thalamic neurons projecting to layer I of the auditory cortical fields of the cat compared to those projecting to layer IV

The distribution of thalamocortical neurons projecting to layer I of the cat auditory cortical fields was examined by the horseradish peroxidase (HRP) method. After HRP injection into layer I of the primary auditory cortex (AI), HRP-labeled neuronal cell bodies were distributed mainly in the medial, dorsal, and ventrolateral divisions of the medial geniculate nucleus (MGN) and suprageniculate nucleus (Sg), and additionally in the lateral and medial divisions of the posterior group of the thalamus (Pol and Pom), lateroposterior thalamic nucleus (Lp), and nucleus of the brachium of the inferior colliculus (BIN). After HRP injection into layer I of the second auditory cortex (AII), labeled neurons were seen mainly in the medial, dorsal, and ventrolateral divisions of the MGN and Sg and additionally in the Pom, Lp, and BIN. After HRP injection into layer I of the anterior auditory field (AAF), labeled neurons were located mainly in the medial and dorsal divisions of the MGN, Sg, Pol, and BIN, and additionally in the ventrolateral divisions of the MGN, Pom, and Lp. After HRP injection into layer I of the dorsal part of the posterior ectosylvian gyrus (Epd), labeled neurons were observed chiefly in the medial and dorsal divisions of the MGN, Sg, and Lp and additionally in the ventrolateral division of the MGN, Pom, and BIN. After HRP injection into layer I of the ventral part of the posterior ectosylvian gyrus (Epv), labeled neurons were distributed chiefly in the medial and dorsal divisions of the MGN and Pol and additionally in the ventrolateral division of the MGN, Sg, and BIN. Thus no labeled neurons were found in the ventral division of the MGN after HRP injection into layer I of all auditory cortical fields examined in the present study. The average soma diameters of neurons that were labeled after HRP injection into layer I were statistically smaller than those of neurons that were labeled after HRP injection into layer IV.     

Projections of thalamic gustatory and lingual areas in the monkey, Macaca fascicularis

The efferent projections of the parvicellular division of the ventroposteromedial nucleus of the thalamus (VMPpc; thalamic taste area) were traced to cortex in Macaca fascicularis by using tritiated amino acid autoradiography. Labeled fascicles could be traced from VPMpc to two discrete regions of cortex. The primary efferent projection was located on ipsilateral insular-opercular cortex adjacent to the superior limiting sulcus and extended as far rostrally as the posterior lateral orbitofrontal cortex. An additional projection was located within primary somatosensory (SI) cortex subjacent to the anterior subcentral sulcus. Following autoradiographic injections in VPM, the trigeminal somatosensory relay, a dense terminal plexus was labeled on SI cortex of both pre- and postcentral gyri, but not within insular-opercular cortex. The autoradiographic data were verified by injecting each cortical projection area with horseradish peroxidase (HRP) and observing the pattern of retrogradely labeled somata within the thalamus. Injections in the precentral gyrus near the anterior subcentral sulcus retrogradely labeled neurons within VPMpc, whereas injections further caudally near the floor of the central sulcus labeled neurons within VPM. Injections of HRP within opercular, insular, or posterior lateral orbitofrontal cortex retrogradely labeled neurons within VPMpc.     

Efferent connections of the centromedian and parafascicular thalamic nuclei: an autoradiographic investigation in the cat

The efferent projections of the centromedian and parafascicular (CM-Pf) thalamic nuclear complex were analyzed by the autoradiographic method. Our findings show that the CM-Pf complex projects in a topographic manner to specific regions of the rostral cortex. These fibers distribute primarily to cortical layers I and III; however, the projection to layer I is more extensive. Following an injection into the rostral portion of the CM-Pf complex, label is found within the lateral rostral cortex, particularly within the presylvian, anterior ectosylvian, and anterior lateral sulci, and within the rostral medial cortex where label is present within the cruciate and anterior splenial sulci and anterior cingulate gyrus. An injection into the caudal dorsal portion of the CM-Pf complex results in label within the more ventral portions of the rostral lateral cortex where it is present within the anterior sylvian gyrus, presylvian regions, and gyrus proreus; and within the rostral medial cortex, where it is present within the rostral cingulate gyrus, and within the cruciate sulcus, and an extensive region ventral to the cruciate sulcus which includes the anterior limbic area. Injections into the caudal ventral portion of the CM-Pf complex result in virtually no cortical label, although a few labeled fibers are found in the subcortical white matter. The subcortical projection from the CM-Pf complex terminates within the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, zona incerta, fields of Forel, hypothalamus, thalamic reticular nucleus, and rostral intralaminar nuclei. Prominent silver grain aggregates are also present within the ventral lateral, ventral anterior, ventral medial, and lateral posterior nuclei, and ventrobasal complex. The aggregates in the thalamus appear to be fibers of passage, but whether these are also terminals cannot be determined with the techniques used in the present study.     

Cortical and brain stem afferents to the ventral thalamic nuclei of the cat demonstrated by retrograde axonal transport of horseradish peroxidase

After horseradish peroxidase (HRP) injections into various parts of the ventral thalamic nuclear group and its adjacent areas, the distribution of labeled neurons was compared in the cerebral cortex, basal ganglia, and the brain stem. The major differences in distribution patterns were as follows: Injections of HRP into the lateral or ventrolateral portions of the ventroanterior and ventrolateral nuclear complex of the thalamus (VA-VL) produced retrogradely labeled neurons consistently in area 4 gamma (lateral part of the anterior and posterior sigmoid gyri, lateral sigmoid gyrus and the lateral fundus of the cruciate sulcus), the medial division of posterior thalamic group (POm), suprageniculate nucleus (SG) and anterior pretectal nucleus ipsilaterally, and in the nucleus Z of the vestibular nuclear complex bilaterally. Injections into the medial or dorsomedial portion of the VA-VL resulted in labeled neurons within the areas 6a beta (medial part of the anterior sigmoid gyrus), 6a delta (anterior part of ventral bank of buried cruciate sulcus), 6 if. fu (posterior part of the bank), fundus of the presylvian sulcus (area 6a beta), medial part of the nucleus lateralis posterior of thalamus and nucleus centralis dorsalis ipsilaterally, and in the entopeduncular nucleus (EPN) and medial pretectal nucleus bilaterally. Only a few neurons were present in the contralateral area 6a delta. After HRP injections into the ventral medial nucleus (VM), major labeled neurons were observed in the gyrus proreus, area 6a beta (mainly in the medial bank of the presylvian sulcus), and EPN ipsilaterally, and in the medial pretectal nucleus and substantia nigra bilaterally. Following HRP injections into the centre médian nucleus (CM), major labeled neurons were found in the areas 4 gamma, 6a beta, and the orbital gyrus ipsilaterally, and in the EPN, rostral and rostrolateral parts of the thalamic reticular nucleus, locus ceruleus, nucleus reticularis pontis oralis et caudalis and nucleus prepositus hypoglossi bilaterally. The contralateral intercalatus nucleus also possessed labeled neurons. With HRP injections into the paracentral and centrolateral nuclei, labeled neurons were observed in the gyrus proreus and the cortical areas between the caudal presylvian sulcus and anterior rhinal sulcus ipsilaterally, and in the nuclei interstitialis and Darkschewitsch bilaterally. Minor differences in the distribution pattern were observed in the superior colliculus, periaqueductal gray, mesencephalic and medullary reticular formations, and vestibular nuclei in all cases of injections.     

Organization of connections underlying the processing of auditory information in the dog

1. The canine temporal cortex includes the ectosylvian, composite posterior and sylvian gyri. 2. The distinctive features of the canine temporal cortex include the ectosylvian sulcus closed in its dorsal side and the substantial development of neocortex located within the posterior composite gyrus. 3. Thalamofugal connections from particular nuclei of the medial geniculate body, posterior thalamus and lateromedial-suprageniculate complex project to specific areas of the canine temporal cortex and are arranged as dominant and non-dominant projections. 4. Local intracortical connections distinguish the ectosylvian and posterior composite areas as unimodal auditory cortex. Long distant connections and polymodal convergence indicate that the composite ectosylvian area of the anterior ectosylvian gyrus and the anterodorsal sylvian areas are higher order association cortex. 5. Analysis of both thalamo-cortical and intracortical connections indicate that auditory processing in the cortex occurs in successive, hierarchically organized stages and in two main, anterior and ventral pathways.     

Sources of thalamic afferent neurons, projecting into the suprasylvian gyrus of the dolphin cerebral cortex

The sources of a thalamic input to different loci of the suprasylvian gyrus (SSG) of the porpoise (Phocaena phocaena) cortex were studied by means of the retrograde HRP and fluorescent tracing methods. After injections of HRP into the anterior part of the SSG most cells were labelled in the lateral part of the ventrobasal complex. Some cells were also labelled in the ventroposteroinferior nucleus, posterior nucleus and caudally in the ventral parvocellular medial geniculate (MG). After injections of bisbenzimide in the middle part of the SSG many labelled cells were found in the ventral parvocellular MG and in the inferior pulvinar. Less cells were labelled in the magnocellular MG, lateral pulvinar and posterior nucleus. After bisbenzimide injection into the posterior part of the SSG the similar distribution of labelled cells was found but a sheet of labelled cells was shifted more laterally.     

An experimental study of ascending connections from the posterior group of thalamic nuclei in the cat

The cortical projections of the posterior group of thalamic nuclei have been studied in the cat by means of the Nauta technique. Small stereotaxic lesions introduced in such a manner as to cause no direct damage to the main thalamic nuclei adjoining the posterior group or to the overlying cortex, indicate the following pattern of projections: Only that part of the posterior group consisting of the suprageniculate and magnocellular medial geniculate nuclei, and particularly the region of transitions between the two, projects to the cortex. The cortical region of fibers is a band comprising the third auditory area (AIII) of Tunturi, the insular cortex, the banks of the anterior ectosylvian sulcus, zones A and B of Carreras and Andersson ('63) in the upper part of the anterior ectosylvian gyrus, the vestibular projection area, the suprasylvian fringe of Woolsey ('61). It is possible that different parts of the suprageniculate-magnocellular complex project to different parts of this cortical band. The suprageniculate-magnocellular complex and certain parts of the band of cortex to which it projects are regions of multi-sensory convergence. Although all parts of the posterior group as presently defined, have been damaged, no part seems to project to the first (SI) or second (SII) somatic sensory areas (other than AIII and zone B, which overlap SII). The main efferent connections of these parts of the poeterior group appear to be with the striatum. The results can be correlated to some extent with previous studies carried out with the method of retrograde cellular degeneration, but there are certain problems in relation to electrophysiological studies.     

Organization of cortical and subcortical projections to the feline insular visual area, IVA.

Extracellular recordings with carbon fiber-filled microelectrodes were used to identify the visually responsive area within the insular cortex (referred to hereafter as the insular visual area, IVA) of anaesthetized cats. Broadly speaking, IVA comprises the cortex surrounding the anterior ectosylvian sulcus (AEs) along its ventral bank and the major portion of the anterior sylvian gyrus. Visually sensitive cells were recorded along the whole length of the AEs. In the same animals, the afferent connections of IVA were studied through the use of the retrograde tracers wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and fluorescent Diamidino yellow (DY), in combination with standard electrophysiological stimulation and recording techniques. The results indicate that: (1) the IVA receives a wide variety of telencephalic inputs, not only from visual, sensorimotor, auditory, limbic and association cortical areas, and from the claustrum, amygdala and basal nucleus of Meynert, as well, but also from the diencephalic projections arising mainly from the lateralis medialis-suprage niculate nuclear complex (LM-Sg) and the ventral medial nucleus (VM). (2) The gyral part of IVA (gIVA) receives afferents mainly from the lateral part of the lateral suprasylvian visual area (LS) throughout almost its entire length, as well as from area 20, the posterior suprasylvian sulcal area (PS), the frontal eye fields, areas 6 and 36, and almost the whole length of the cortical area lying along the anterior ectosylvian sulcus (AEs). (3) By contrast with (2), the sulcal part of IVA (sIVA) which corresponds to the anterior part of the anterior ectosylvian visual area (AEV) of Norita et al. ('86), receives cortical projections mainly from the lateral and medial parts of the anterior half of LS, area 20, PS, the frontal eye fields, area 36, and most parts of the cortical area extending along the AEs. (4) Subcortically, IVA receives thalamic afferents mainly from VM and LM-Sg. The connections between IVA and LM-Sg are organized topographically, with the more anterior part of IVA being related to the more ventral portion of LM-Sg, and with sIVA being related chiefly to the mid-portions of LM-Sg. These results thus suggest that IVA may function as an integrative centre among structures belonging to the extrageniculostriate system, the sensorimotor system, as well as to the limbic system. Furthermore, our electrophysiological and anatomical findings, together with previous reports concerning AEV, suggest that the posterior part of AEV (AEV proper) is distinctive from gIVA, and that the sIVA apparently serves as a transitional region between AEV and gIVA.     

Connections of the multiple visual cortical areas with the lateral posterior-pulvinar complex and adjacent thalamic nuclei in the cat

The present report describes the patterns of cat thalamocortical interconnections for each of the 13 retinotopically ordered visual areas and additional visual areas for which no retinotopy has yet emerged. Small injections (75 nl) of a mixture of horseradish peroxidase and [3H]leucine were made through a recording pipette at cortical injection sites identified by retinotopic mapping. The patterns of thalamic label show that the lateral posterior-pulvinar complex of the cat is divided into three distinct functional zones, each of which contains a representation of the visual hemifield and shows unique afferent and efferent connectivity patterns. The pulvinar nucleus projects to areas 19, 20a, 20b, 21a, 21b, 5, 7, the splenial visual area, and the cingulate gyrus. The lateral division of the lateral posterior nucleus projects to areas 17, 18, 19, 20a, 20b, 21a, 21b, and the anterior medial (AMLS), posterior medial (PMLS), and ventral (VLS) lateral suprasylvian areas. The medial division of the lateral posterior nucleus projects to areas AMLS, PMLS, VLS, and the anterior lateral (ALLS), posterior lateral (PLLS), dorsal (DLS) lateral suprasylvian areas, and the posterior suprasylvian areas. In addition, many of these visual areas are also interconnected with subdivisions of the dorsal lateral geniculate nucleus (LGd). Every retinotopically ordered cortical area (except ALLS and AMLS) is reciprocally interconnected with the parvocellular C layers of the LGd. The medial intralaminar nucleus of the LGd projects to areas 17, 18, 19, AMLS, and PMLS. Finally, each cortical area (except area 17) receives a projection from thalamic intralaminar nuclei. These results help to define the pathways by which visual information gains access to the vast system of extrastriate cortex in the cat.