Pulvinar nuclei of the behaving rhesus monkey: visual responses and their modulation

We have examined the properties of neurons in three subdivisions of the pulvinar of alert, trained rhesus monkeys 1) an inferior, retinotopically mapped area (PI), 2) a lateral, retinotopically organized region (PL), and 3) a dorsomedial visual portion of the lateral pulvinar (Pdm), which has a crude retinotopic organization. We tested the neurons for visual responses to stationary and moving stimuli and for changes in these responses produced by behavioral manipulations. All areas contain cells sensitive to stimulus orientation as well as neurons selective for the direction of stimulus movement; however, the majority of cells in all three regions are either broadly tuned or nonselective for these attributes. Nearly all cells respond to stimulus onset, a significant number also give a response to stimulus termination, and rarely a cell gives only off responses. Nearly all cells increase their discharge rate to visual stimuli. Receptive fields in the two retinotopically mapped regions, PI and PL, have well-defined borders. The sizes of these receptive fields show a positive correlation with the eccentricity of the receptive fields. The receptive fields in the remaining region, Pdm, are frequently very large, but with these large fields excluded, show a similar correlation with eccentricity. All pulvinar cells tested (n = 20) were mapped in retinal coordinates; the receptive fields are positioned in relation to the retina. We found no cells with gaze-gated characteristics (2), nor cells mapped in a spatial coordinate system. The response latencies in PI and PL are shorter and less variable than the latencies in Pdm. Active use of a stimulus can produce an enhancement or attenuation of the visual response. Eye-movement modulation was found in all three subdivisions in about equal frequencies. Attentional modulation was common in Pdm and was rare in PI and PL. The modulation is spatially selective in Pdm and nonselective in PI for a small number of tested cells. These data demonstrate functional differences between Pdm and the other two areas and suggest that Pdm plays a role in selective visual attention, whereas PI and PL probably contribute to other aspects of visual perception.     

Gating and control of primary visual cortex by pulvinar

The primary visual cortex (V1) receives its driving input from the eyes via the lateral geniculate nucleus (LGN) of the thalamus. The lateral pulvinar nucleus of the thalamus also projects to V1, but this input is not well understood. We manipulated lateral pulvinar neural activity in prosimian primates and assessed the effect on supra-granular layers of V1 that project to higher visual cortex. Reversibly inactivating lateral pulvinar prevented supra-granular V1 neurons from responding to visual stimulation. Reversible, focal excitation of lateral pulvinar receptive fields increased the visual responses in coincident V1 receptive fields fourfold and shifted partially overlapping V1 receptive fields toward the center of excitation. V1 responses to regions surrounding the excited lateral pulvinar receptive fields were suppressed. LGN responses were unaffected by these lateral pulvinar manipulations. Excitation of lateral pulvinar after LGN lesion activated supra-granular layer V1 neurons. Thus, lateral pulvinar is able to powerfully control and gate information outflow from V1.     

Functional imaging of the human lateral geniculate nucleus and pulvinar

In the human brain, little is known about the functional anatomy and response properties of subcortical nuclei containing visual maps such as the lateral geniculate nucleus (LGN) and the pulvinar. Using functional magnetic resonance imaging (fMRI) at 3 tesla (T), collective responses of neural populations in the LGN were measured as a function of stimulus contrast and flicker reversal rate and compared with those obtained in visual cortex. Flickering checkerboard stimuli presented in alternation to the right and left hemifields reliably activated the LGN. The peak of the LGN activation was found to be on average within +/-2 mm of the anatomical location of the LGN, as identified on high-resolution structural images. In all visual areas except the middle temporal (MT), fMRI responses increased monotonically with stimulus contrast. In the LGN, the dynamic response range of the contrast function was larger and contrast gain was lower than in the cortex. Contrast sensitivity was lowest in the LGN and V1 and increased gradually in extrastriate cortex. In area MT, responses were saturated at 4% contrast. Response modulation by changes in flicker rate was similar in the LGN and V1 and occurred mainly in the frequency range between 0.5 and 7.5 Hz; in contrast, in extrastriate areas V4, V3A, and MT, responses were modulated mainly in the frequency range between 7.5 and 20 Hz. In the human pulvinar, no activations were obtained with the experimental designs used to probe response properties of the LGN. However, regions in the mediodorsal right and left pulvinar were found to be consistently activated by bilaterally presented flickering checkerboard stimuli, when subjects attended to the stimuli. Taken together, our results demonstrate that fMRI at 3 T can be used effectively to study thalamocortical circuits in the human brain.     

Neocortical connections in fetal cats

The major extrinsic projections to and from visual and auditory areas of cerebral cortex were examined in fetal cats between 46 and 60 days of gestation (E46-E60) using axonal transport of horseradish peroxidase either alone or in combination with tritiated proline. Projections to visual cortex from the dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex exist by E46, and those from the contralateral hemisphere, claustrum, putamen, and central lateral nucleus of the thalamus are present by E54-E56. In addition, cells in the medial geniculate nucleus project to auditory cortex by E55. At E54-E56 efferent cortical projections reach the contralateral hemisphere, claustrum, putamen, lateral-posterior/pulvinar complex and reticular nucleus of the thalamus. Cells in visual cortex also project to the dorsal and ventral lateral geniculate nuclei, pretectum, superior colliculus and pontine nuclei, and cells in auditory cortex project to the medial geniculate nucleus. Except for interhemispheric projections, all pathways demonstrated are ipsilateral, and projections linking cerebral cortex with claustrum, dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex are reciprocal. The reciprocal projections formed with the dorsal lateral geniculate nucleus, lateral-posterior/pulvinar complex and the claustrum show a greater degree of topological organization compared to the projections formed with the contralateral hemisphere and superior colliculus, which show little or no topological order. Therefore, the results of the present study show that the major extrinsic projections of the cat's visual and auditory cortical areas with subcortical structures are present by the eighth week of gestation, and that the origins and terminations of many of these projections are arranged topologically.     

Visual thalamocortical projections in the flying fox: parallel pathways to striate and extrastriate areas

We studied thalamic projections to the visual cortex in flying foxes, animals that share neural features believed to resemble those present in the brains of early primates. Neurones labeled by injections of fluorescent tracers in striate and extrastriate cortices were charted relative to the architectural boundaries of thalamic nuclei. Three main findings are reported: First, there are parallel lateral geniculate nucleus (LGN) projections to striate and extrastriate cortices. Second, the pulvinar complex is expansive, and contains multiple subdivisions. Third, across the visual thalamus, the location of cells labeled after visual cortex injections changes systematically, with caudal visual areas receiving their strongest projections from the most lateral thalamic nuclei, and rostral areas receiving strong projections from medial nuclei. We identified three architectural layers in the LGN, and three subdivisions of the pulvinar complex. The outer LGN layer contained the largest cells, and had strong projections to the areas V1, V2 and V3. Neurones in the intermediate LGN layer were intermediate in size, and projected to V1 and, less densely, to V2. The layer nearest to the origin of the optic radiation contained the smallest cells, and projected not only to V1, V2 and V3, but also, weakly, to the occipitotemporal area (OT, which is similar to primate middle temporal area) and the occipitoparietal area (OP, a "third tier" area located near the dorsal midline). V1, V2 and V3 received strong projections from the lateral and intermediate subdivisions of the pulvinar complex, while OP and OT received their main thalamic input from the intermediate and medial subdivisions of the pulvinar complex. These results suggest parallels with the carnivore visual system, and indicate that the restriction of the projections of the large- and intermediate-sized LGN layers to V1, observed in present-day primates, evolved from a more generalized mammalian condition.     

An investigation of collateral projections of the dorsal lateral geniculate nucleus and other subcortical structures to cortical areas V1 and V4 in the macaque monkey: A double label retrograde tracer study

Summary Previous anterograde studies in the macaque monkey have shown that, in addition to the projection to striate cortex (V1), the dorsal lateral geniculate nucleus (DLG) has a sparse, horizontally segregated projection to layers IV and V of prestriate cortex (V4). However, the distribution and degree of axon collateralization of DLG cells which give rise to these projections are unknown. This study was designed to answer these questions. The DLG (along with the pulvinar and other subcortical regions) was examined for the presence of single- or doublelabeled cells after injections of two different (fluorescent or HRP) retrograde tracers into corresponding retinotopic points in visual cortical areas V1 and V4. In the DLG, it was found that cells projecting to V4, which reside in or near the tectorecipient interlaminar zones of the DLG, do not project to V1 and thus represent a separate population of cells. The organization of the macaque geniculo-prestriate projection thus seems quite different from that of carnivores. Both single- and double-labeled cells were found in other subcortical areas, e.g., single-labeled cells were found in the claustrum, hypothalamus and lateral pulvinar, and a double-labeled cell population was found in the inferior pulvinar.Abbreviations BSC Brachium of the superior colliculus - Cd Caudate nucleus - Cl Claustrum - DLG Dorsal lateral geniculate nucleus - GP Globus pallidus - Hce1 Medial hypothalamic cholinesterase group of Mesulam et al. (1983) - Hce2 Lateral hypothalamic cholinesterase group of Mesulam et al. (1983) - Hip Hippocampus - ot optic tract - PI Inferior pulvinar - PL Lateral pulvinar - PM Medial pulvinar - Put Putamen - Ret Reticular nucleus of thalamus - Thal Thalamus - v ventricle     

Attention modulates responses in the human lateral geniculate nucleus

Attentional mechanisms are important for selecting relevant information and filtering out irrelevant information from cluttered visual scenes. Selective attention has previously been shown to affect neural activity in both extrastriate and striate visual cortex. Here, evidence from functional brain imaging shows that attentional response modulation is not confined to cortical processing, but can occur as early as the thalamic level. We found that attention modulated neural activity in the human lateral geniculate nucleus (LGN) in several ways: it enhanced neural responses to attended stimuli, attenuated responses to ignored stimuli and increased baseline activity in the absence of visual stimulation. The LGN, traditionally viewed as the gateway to visual cortex, may also serve as a 'gatekeeper' in controlling attentional response gain.     

Attentional effects in the visual pathways: a whole-brain PET study

Attentional effects in the visual pathways were investigated by contrasting the distribution of regional cerebral blood flow (rCBF) measured by H₂ ¹⁵O positron emission tomography (PET) during performance of a shape-matching task with the distribution of rCBF during a less demanding color-matching task. The two tasks were performed using the same stimuli: pairs of colored random shapes shown at a fixed rate (2 s per pair). In the shape-matching task, the subjects determined whether the two stimuli were the same in shape regardless of differences in size or color. In the color-matching task, the subjects determined whether the two stimuli were the same in color regardless of differences in size or shape. Mean reaction time for shape-matching exceeded mean reaction time for color-matching by nearly 200 ms. The corresponding shape-color comparison showed extensive bilateral increases in rCBF in visual areas in the occipital and parietal lobes, including the primary visual cortex. Subcortical activations were found in cerebellum (particularly the vermis) and in the thalamus with the focus in a region comprising the lateral geniculate nucleus, the pulvinar, and adjacent parts of the reticular nucleus. Frontal activations were found in a region that seems implicated in visual short-term memory (posterior parts of the superior sulcus and the middle gyrus). The reverse, color-shape comparison showed bilateral increases in rCBF in the anterior cingulate gyri, superior frontal gyri, and superior and middle temporal gyri. The attentional effects found by the shape-color comparison in the thalamus and the primary visual cortex may have been generated by feedback signals preserving visual representations of selected stimuli in short-term memory. Electronic Publication     

Saccade-related and visual activities in the pulvinar nuclei of the behaving rhesus monkey

Summary We studied three subdivisions of the pulvinar: a retinotopically organized inferior area (PI), a retinotopically mapped region of the lateral pulvinar (PL), and a separate, visually responsive component of the lateral pulvinar (Pdm). Single neurons were recorded in these regions from awake, trained rhesus monkeys, and we correlated the discharge patterns of the cells with eye movements. About 60% of the neurons discharged after saccadic eye movements in an illuminated environment and had either excitatory, inhibitory, or biphasic (inhibitory-excitatory) response patterns. These responses were most often transient in nature. Neurons with excitatory activity had a mean onset latency of 72 ms after the termination of the eye movement. Latencies for cells with inhibitory responses averaged 58 ms. In sharp contrast, the cells with biphasic response patterns became active before the termination of the eye movement. A unique set of these neurons termed saccade cells, were active with visually guided eye movements in the light, with the same eye movements made to a briefly pulsed target in the dark, and for similar eye movements made spontaneously in total darkness. The activity was present with the appropriate saccade, independent of the beginning eye position. Biphasic response patterns were typical of these saccade cells. Saccade cells were most common in Pdm and PI. About half of the saccade cells also had some visual response that was independent of eye movement. A second group of cells was active with saccadic eye movements in the light but not in the dark. Some of these cells had clear visual responses that could account for their activity following eye movements; others had no clear visual receptive field. Because of these and other physiological data, we propose that the saccade cells found in Pdm may function in a system dealing with visual spatial attention, while those found in PI may have a role in dealing with the visual consequences of eye movements.     

Afferent connections of the prelunate visual association cortex (areas V4 and DP)

Summary The afferent and efferent connections of the prelunate visual association area V4 of macaque monkeys were investigated by means of the horseradish peroxidase (HRP) method. The specific thalamic afferents from the dorsolateral segment of the medial pulvinar and the lateral segment of the inferior pulvinar were topographically organized. A band of cells was labelled in the intralaminar nuclei (nucl. centr. med. and lat., reaching into LD and the most dorsal part of VL), and a few cells in the interlaminar layers of the lateral geniculate body. Other diencephalic afferents included the claustrum, the nucleus basalis Meynert and the pars compacta of the substantia nigra. Ipsilateral cortical areas which projected into V4 included area 18 (V2), the inferior parietal cortex, the anterior and posterior parts of the superior temporal sulcus, the frontal eye fields and the temporo-basal association cortex on the lateral half of the parahippocampal gyrus and around the occipito-temporal sulcus. In the contralateral cortex, discontinuous regions in areas V4 and V5 on the prelunate gyrus and some cells at the 17/18-border were labelled. All regions in which labelled cells were found and, in addition a restricted region in the dorsal cap of the head and the tail of the caudate nucleus showed fibre and terminal labelling. In addition mesencephalic afferents and efferents were identified but not investigated in detail. An attempt to estimate the quantitative contribution of the various afferent systems to the prelunate cortex was made by counting the labelled cells in the different areas. The afferent and efferent organization of the prelunate visual association area indicates that it is incorporated in a network of cortical and subcortical regions involved in various aspects of visual behavior.     

Quantitative analyses of principal and secondary compound parieto-occipital feedback pathways in cat

The purpose of our study was to quantify the magnitude of principal and secondary pathways emanating from the middle suprasylvian (MS) region of visuoparietal cortex and terminating in area 18 of primary visual cortex. These pathways transmit feedback signals from visuoparietal cortex to primary visual cortex. (1) WGA-HRP was injected into area 18 to identify inputs from visual structures. In terms of numbers of neurons, feedback projections to area 18 from MS sulcal cortex (areas PMLS, AMLS and PLLS) comprise 26% of inputs from all visual structures. Of these neurons, between 21% and 34.9% are located in upper layers 2–4 and the dominant numbers are located in deep layers 5 and 6. Areas 17 (11.8%) and 19 (11.2%) provide more modest cortical inputs, and another eight areas provide a combined total of 4.3% of inputs. The sum of neurons in all subcompartments of the lateral geniculate nucleus (LGN) accounts for another 34.8% of the input to area 18, whereas inputs from the lateral division of the lateral-posterior nucleus (LPl) account for the final 11.9%. (2) Injection of tritiated-(³H)-amino acids into MS sulcal cortex revealed substantial direct projections from MS cortex that terminated in all layers of area 18, but with a markedly lower density in layer 4. Projections from MS cortex to both areas 17 and 19 are of similar density and characteristics, whereas those to other cortical targets have very low densities. Quantification also revealed minor-to-modest axon projections to all components of LGN and a massive projection throughout the LP-Pul complex. (3) Superposition of the labeled terminal and cell fields identified secondary, compound feedback pathways from MS cortex to area 18. The largest secondary pathway is massive and it includes the LPl nucleus. Much more modest secondary pathways include areas 17 and 19, and LGN. The relative magnitudes of the secondary pathways suggest that the one through LPl exerts a major influence on area 18, whereas the others exert more modest or minor influences. MS cortex in the contralateral hemisphere also innervates area 18 directly. These data are important for interpreting the impact of deactivating feedback projections from visuoparietal cortex on occipital cortex.Abbreviations A layer A of LGN - A1 layer A1 of LGN - ALLS anterolateral visual area of the lateral suprasylvian sulcus (Palmer et al. 1978) - AMLS anteromedial visual area of the lateral suprasylvian sulcus (Palmer et al. 1978) - Aud auditory cortex of the middle ectosylvian gyrus - CC corpus callosum - Cg cingulate gyrus - Cm magnocellular layers of LGN - Cp parvocellular layers of LGN - LGN dorsal lateral geniculate nucleus - LP lateral posterior nucleus - LPl lateral division of the lateral posterior nucleus - LPm medial division of the lateral posterior nucleus (Graybiel and Berson 1980, Berson and Graybiel 1978; Raczkowski and Rosenquist 1983) - MIN medial interlaminar nucleus subdivision of LGN - MS cortex bounding the middle suprasylvian sulcus (areas AMLS, ALLS, PMLS, and PLLS) - OR optic radiation - PE posterior ectosylvian visual cortex - PLLS posterolateral visual area of the lateral suprasylvian sulcus (Palmer et al. 1978) - PMLS posteromedial visual area of the lateral suprasylvian sulcus (Palmer et al. 1978) - Pul pulvinar nucleus - SVA splenial visual area - V1 primary visual cortex - V2 secondary visual cortex - V3 third visual area - V5/MT fifth visual area/middle temporal area - WGA-HRP wheat germ agglutinin conjugated to horseradish peroxidase - Wing wing of LGN - 7 area 7 - 17 area 17 - 18 area 18 - 19 area 19     

Some topographical connections of the striate cortex with subcortical structures in Macaca fascicularis

Summary Subcortical connections of the striate cortex with the superior colliculus (SC), the lateral pulvinar (Pl), the inferior pulvinar (Pi) and the dorsal lateral geniculate nucleus (LG) were studied in the macaque monkey, Macaca fascicularis, following cortical injections of tritiated proline and/or horseradish peroxidase. All four structures were shown to receive topographically organized projections from the striate cortex. The exposed surface of the striate cortex was found to be connected to the rostral part of the SC and the caudal part of the LG. Injections of the exposed striate cortex close to its rostral border resulted in label in adjoining parts of the Pl and Pi. The ventral half and dorsal half of the calcarine fissure were connected with the medial and lateral parts of the SC, the ventrolateral and dorsomedial portions of the Pl and Pi and the lateral and medial parts of the LG, respectively. Injections located at the lateral posterior extreme of the calcarine fissure resulted in label at the optic disc representation in the LG. The horseradish peroxidase material demonstrated that LG neurons in all laminae and interlaminar zones project to the striate cortex.Abbreviations BIC brachium of the inferior colliculus - BSC brachium of the superior colliculus - C cerebellum - CG central grey - i interlaminar zone(s) of the dorsal lateral geniculate nucleus - IC inferior colliculus - ICc central nucleus of the inferior colliculus - LG dorsal lateral geniculate nucleus - m magnocellular layer(s) of the dorsal lateral geniculate nucleus - MG medial geniculate body - p parvocellular layer(s) of the dorsal lateral geniculate nucleus - P pulvinar complex - Pi inferior pulvinar - PG pregeniculate nucleus - Pl lateral pulvinar - Pm medial pulvinar - s superficial layer(s) of the dorsal lateral geniculate nucleus - SC superior colliculus - sgs stratum griseum superficiale of the superior colliculus - R reticular nucleus of the thalamus - VP ventroposterior group - 17 Area 17 Supported by NEI Grants EY-07007 (J. Graham) and EY-02686 (J.H. Kaas)     

Thalamic projections to visual and visuomotor areas (V6 and V6A) in the Rostral Bank of the parieto-occipital sulcus of the Macaque

The medial posterior parietal cortex of the primate brain includes different functional areas, which have been defined based on the functional properties, cyto- and myeloarchitectural criteria, and cortico-cortical connections. Here, we describe the thalamic projections to two of these areas (V6 and V6A), based on 14 retrograde neuronal tracer injections in 11 hemispheres of 9 Macaca fascicularis. The injections were placed either by direct visualisation or using electrophysiological guidance, and the location of injection sites was determined post mortem based on cyto- and myeloarchitectural criteria. We found that the majority of the thalamic afferents to the visual area V6 originate in subdivisions of the lateral and inferior pulvinar nuclei, with weaker inputs originating from the central densocellular, paracentral, lateral posterior, lateral geniculate, ventral anterior and mediodorsal nuclei. In contrast, injections in both the dorsal and ventral parts of the visuomotor area V6A revealed strong inputs from the lateral posterior and medial pulvinar nuclei, as well as smaller inputs from the ventrolateral complex and from the central densocellular, paracentral, and mediodorsal nuclei. These projection patterns are in line with the functional properties of injected areas: “dorsal stream” extrastriate area V6 receives information from visuotopically organised subdivisions of the thalamus; whereas visuomotor area V6A, which is involved in the sensory guidance of arm movement, receives its primary afferents from thalamic nuclei that provide high-order somatic and visual input.     

Projections of the pulvinar-lateral posterior complex to visual cortical areas in the cat

The projections of the pulvinar-lateral posterior complex of the cat were studied using the autoradiographic tracing method and related to 15 previously defined cortical areas. The results indicate that each of three separate zones within the pulvinar-lateral posterior complex has a different pattern of projection. The most lateral zone, the pulvinar, sends fibers to at least seven cortical areas, most of which are known to have input from other visual areas within the brain: the splenial visual area, the cingulate gyrus, and areas 5, 7, 19, 20a and 21a. A zone located just medial to the pulvinar, the lateral division of the lateral posterior complex, projects to at least eight visual areas in the cortex: areas 17, 18, 19, 20a, 21a, 21b, the posteromedial lateral suprasylvian area and the ventral lateral suprasylvian area. The most medial zone, the intermediate division of the lateral posterior complex, projects to at least four cortical areas: 20a, the posterior suprasylvian area, the posterolateral lateral suprasylvian area and the dorsal lateral suprasylvian area. Of the 15 cortical areas that receive fibers from the pulvinar-lateral posterior complex, only three (areas 19, 20a and 21a) receive projections from more than one of these thalamic zones, and only one of the cortical areas (20a) receives fibers from all three zones.Thus, the data support the division of the pulvinar lateral posterior complex into three zones on the basis of their unique and largely non-overlapping projections to the visual cortex.     

Fewer driver synapses in higher order than in first order thalamic relays

We used electron microscopy to determine the relative numbers of the three synaptic terminal types, RL (round vesicle, large terminal), RS (round vesicles, small terminal), and F (flattened vesicles), found in several representative thalamic nuclei in cats chosen as representative examples of first and higher order thalamic nuclei, where the first order nuclei relay subcortical information mainly to primary sensory cortex, and the higher order nuclei largely relay information from one cortical area to another. The nuclei sampled were the first order ventral posterior nucleus (somatosensory) and the ventral portion of the medial geniculate nucleus (auditory), and the higher order posterior nucleus (somatosensory) and the medial portion of the medial geniculate nucleus (auditory). We found that the relative percentage of synapses from RL terminals varied significantly among these nuclei, these values being higher for first order nuclei (12.6% for the ventral posterior nucleus and 8.2% for the ventral portion of the medial geniculate nucleus) than for the higher order nuclei (5.4% for the posterior nucleus, and 3.5% for the medial portion of the medial geniculate nucleus). This is consistent with a similar analysis of first and higher order nuclei for the visual system (the lateral geniculate nucleus and pulvinar, respectively). Since synapses from RL terminals represent the main information to be relayed, whereas synapses from F and RS terminals are modulatory in function, we conclude that there is relatively more modulation of the thalamic relay in the cortico-thalamo-cortical higher order pathway than in first order relays.     

Saccadic eye movements following kainic acid lesions of the pulvinar in monkeys

Summary Behavioral and anatomical experiments have suggested that the pulvinar might play a role in the generation of saccadic eye movements to visual targets. To test this idea, we trained monkeys to make visually-guided saccades by requiring them to detect the dimming of a small target. We used three different saccade paradigms. On single-step trials, saccades were made from a central fixation point (FP) to a target at 12, 24 or 36° to the left or right. On overlap trials, the FP remained lit during presentation of a target at 12 or 24°. On double-step trials, the target stepped first to 24°, and then back to 12° on the same side. Animals were trained to criterion, received kainic acid lesions of the pulvinar, and were retested on all three tasks. The lesions were very large, destroying almost all of the visually responsive pulvinar. They also encroached on the lateral geniculate nucleus, thereby producing small foveal scotomas, and this resulted in some behavioral changes, including difficulty in maintaining fixation on the target and in detecting its dimming. Results on the saccade tests suggest that the pulvinar is not crucial for initiation of saccadic eye movements. Saccade latency and amplitude were unimpaired on both single-step and overlap trials. Saccadic performance was also normal on double-step trials. In a second experiment, we measured the average length of fixations during spontaneous viewing of a complex visual scene. Fixation lengths did not differ from those of unoperated control monkeys. We suggest that the neglect, increased saccadic latencies, and prolonged fixations attributed to pulvinar damage in previous studies were probably the result instead of inadvertent damage to tectal afferents. The present results, together with single unit data, point to a role for the pulvinar not in the generation of saccades, but rather in the integration of saccadic eye movements with visual processing.     

Topographical and topological organization of the thalamocortical projection to the striate and prestriate cortex in the marmoset (Callithrix jacchus)

Summary In eleven hemispheres of nine marmoset monkeys (Callithrix jacchus), we have investigated the thalamo-cortical organization of the projections from the pulvinar to the striate and prestriate cortex. In each experiment, single or multiple injections of various retrograde fluorescent tracers were injected into adjacent regions or areas. In two experiments, horseradish peroxidase (HRP) was injected into the lateral geniculate nucleus (LGN) and the lateral pulvinar, respectively. The results show that the thalamo-cortical projection from LGN to striate cortex and from pulvinar to the prestriate cortex are similarly organized, but the geniculo-striate projection is more precise than the pulvinar-prestriate projection. The pulvinar-prestriate projection is topographically organized and preserves topological neighbourhood relations. Projection zones to the various visual areas are concentrically wrapped around each other. The projection zone to area 18 constitutes a central core region. It begins ventro-laterally in PuL where the pulvinar is in contact with the LGN. This contact zone we called the hilus region of the pulvinar. The area 18-projection zone stretches as a central cone into the posterior pulvinar through PuL and into PuM. It is surrounded by the projection zone to the posterior belt of area 19 and this in turn is surrounded by the projection zone to the anterior belt of area 19. The projection zones to area 19 are then surrounded medially and dorsally by zones projectiong to the temporal and parietal association cortex, respectively. The projection zone to area MT is located medio-ventrally in the posterior pulvinar (PuIP and surrounding nuclei) and coincides with a densely myelinated region. Area 17 also receives input from the pulvinar but probably predominantly in the region of the central visual field. The pulvinar zone projecting to area 17 is located ventrolaterally from the central core region projecting to area 18 and is contiguous laterally with the LGN. If the positions of the vertical and the horizontal meridian in the pulvinar correspond to those in the respective cortical projection zones, a second order visual field representation such as found in area 18, with the horizontal meridian split at an excentricity of about 7–10°, can also be recognized in the pulvinar.Abbreviations A Subcortical nuclei and subnuclei, cf. — Stephan et al. (1980) - AD Nucleus anterior dorsalis thalami - AV Nucleus anterior ventralis thalami - CeD Nucleus centralis dorsalis thalami - CeL Nucleus centralis lateralis thalami - CeMe Centrum medianum thalami - CoS Colliculus superior - FRPO Formatio reticularis pontis, pars oralis - GM Corpus geniculatum mediale - IBCI Nucleus interstitialis brachii colliculi inferioris - LGN Corpus geniculatum laterale dorsale - vLGN Corpus geniculatum laterale ventrale - LD Nucleus lateralis dorsalis thalami - LI Nucleus limitans thalami - LP Nucleus lateralis posterior thalami - MD Nucleus medialis dorsalis thalami - OL Nucleus olivaris superior lateralis - OM Nucleus olivaris superior medialis - Pbg Nucleus parabigeminalis - Pul Pulvinar inferior; PulP Pulvinar inferior posterior - PuL Pulvinar lateralis - PuM Pulvinar medialis - PuO Pulvinar oralis - RT Nucleus reticularis thalami - Sg Nucleus suprageniculatus - VA Nucleus ventralis anterior thalami - VL Nucleus ventralis lateralis thalami - VPL Nucleus ventralis posterior lateralis thalami - VPM Nucleus ventralis posterior medialis thalami - IV Nucleus nervi trochlearis - B Cortical areas and subareas, (after Spatz 1977a; Spatz et al. 1987 Allman and Kaas 1975): - 17 Area striata (V I) - 18 Area 18 (V II) - 19DI Area 19 dorso-intermediate - 19DL Area 19 dorso-lateral - 19DM Area 19 dorso-medial - 19M Area 19 medial - 19V Area 19 ventral - MT Middle temporal area     

Temporal variations of visual evoked potentials in structures of the visual analyzer in different phases of saccadic eye movements in cats

Evoked potentials of the superior colliculus, pulvinar, lateral geniculate body, and striate cortex in response to a short flash of light delivered in a homogeneous visual field were studied in cats with a rigidly fixed head during gaze holding, before a saccade, and at different phases of saccadic eye movements to an angle of 20°. It is shown that proprioceptive afferent impulses from external ocular muscles participate along with the efferent copy in visual suppression during the saccade, and that the collicular and pulvinar structures are mainly responsible for the suppression. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 6, pp. 574–577, June 1995 Presented by the late O. S. Adrianov, Member of the Russian Academy of Medical Sciences     

Connections to the lateral posterior-pulvinar thalamic complex from the reticular and ventral lateral geniculate thalamic nuclei: a topographical study in the cat

The projections from the reticular thalamic nucleus and the ventral lateral geniculate nucleus to the lateral posterior-pulvinar thalamic complex were studied in the adult cat using the retrograde transport of horseradish peroxidase. Small, stereotaxically guided injections of the enzyme were placed in the various nuclei of this complex, including the pulvinar, lateralis intermedius oralis, lateralis intermedius caudalis, lateralis posterior lateralis, lateralis posterior medialis and lateralis medialis nuclei. The distribution of labeled neurons indicates that these nuclei receive topographically organized projections from the reticular and ventral lateral geniculate nuclei. The pulvinar nucleus receives only very scarce projections from the reticular thalamic nucleus originating in its posterodorsal and posteroventral sectors. The reticular projection to the nucleus lateralis intermedius oralis is even sparser. The nuclei lateralis intermedius caudalis, lateralis posterior lateralis and lateralis posterior medialis receive substantial projections from the suprageniculate sector of the reticular thalamic nucleus. The nucleus lateralis medialis receives an abundant projection from the three sectors (suprageniculate, pregeniculate and infrageniculate) of the reticular thalamic nucleus. Except for the lateralis intermedius caudalis, all nuclei of the lateral posterior-pulvinar complex receive consistent projections from the ventral lateral geniculate nucleus, the nucleus lateralis medialis receiving the densest one. Our findings suggest that visual, auditory, somatosensory, motor and limbic impulses from thalamic nuclei and from primary sensory and association cortical areas modulate the activity of the nucleus lateralis medialis via the reticular thalamic nucleus. The remaining nuclei of the lateral posterior-pulvinar complex are mainly modulated by sectors of the reticular thalamic nucleus that receive afferent connections from visual structures. The intrathalamic projections arising from the ventral lateral geniculate nucleus may be the way through which visuomotor inputs reach the different components of the lateral posterior-pulvinar thalamic complex.     

Organization of the visual pathways in the newborn kitten

We have used retrograde and anterograde transport to examine the major visual pathways in newborn kittens. Retinal projections from both eyes to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) are present and topographically organized. The dLGN projects topographically to areas 17 and 18 and receives reciprocal projections from cells in layer VI of areas 17, 18, 19 and suprasylvian cortex on the same side of the brain. Area 19 also has a sparse thalamic input but probably not from the dLGN. The laminar distribution of [3H]proline transported from dLGN to area 17 was quantified: label was spread through all layers, with a minimum at the border of layers I/II. Layer I was always labelled less heavily than IV. These results are critically compared with those based on other tracing techniques. Cells of layer V in areas 17, 18, 19 and the suprasylvian cortex project topographically to the superficial layers of the ipsilateral SC. Area 19 and the lateral suprasylvian cortex also send a crossed projection to restricted parts of the opposite SC. Thus these visual projections are not only present and topographically ordered on the day of birth, but, unlike certain highly exuberant interhemispheric and cortico-cortical projections, they are qualitatively remarkably mature, some days before the onset of visual activity. The major subcortical projections to and from the visual cortex appear to be constructed without the benefit of visual experience and much of the activity-dependent plasticity of cortical cells may well involve only local modulation of synaptic input.