Cat lateral suprasylvian cortex: Y-cell inputs and corticotectal projection

Retinal Y-cells activate most cells in the deep layers of the cat's superior colliculus via an indirect pathway involving the occipital cortex. The lateral suprasylvian area seems to be an important source of visual input to the deep collicular strata but it is unclear whether Y-cell influences reach this extrastriate area and, hence, whether this area participates in the indirect Y-cell pathway. In this study, retinal influences on the posteromedial lateral suprasylvian area (PMLS) were studied in anesthetized cats. Responses to electrical stimulation of the optic disk (OD) and optic chiasm (OX) were recorded in single units in PMLS and in neurons of the dorsal lateral geniculate nucleus (LGNd) that were antidromically driven from PMLS. Virtually all PMLS cells (99%; 99/100) exhibited small differences (less than or equal to 0.8 ms) between OD- and OX-activation latency, indicating that they were driven by a pathway originating in rapidly conducting Y-cell axons. A small number of PMLS cells (17%; 20/118) had very short activation latencies (less than or equal to 3.2 ms from OX), comparable to those of cells in areas 17 and 18 receiving monosynaptic inputs from geniculate Y-cells. Further, LGNd cells with latency behaviors typical of Y-cells could be antidromically driven from PMLS, confirming that geniculate Y-cells project directly to PMLS. Most PMLS cells (83%; 98/118), though exhibiting small OD-OX latency differences, had absolute latencies too long to be attributed to direct inputs from geniculate Y-cells (3.3-8.5 ms from OX). Thus Y-cells in the LGNd influence most PMLS cells by way of a multisynaptic pathway. PMLS cells antidromically activated from the superior colliculus were driven only by this multisynaptic Y-cell input. Total conduction time from the retina through PMLS to the colliculus corresponds closely to the latency of the indirect Y-cell activation observed in the deep collicular layers. These results support the view that the lateral suprasylvian cortex constitutes an important source of visual input to the cat's deep collicular layers and, more generally, that the extrastriate visual cortex may figure prominently in the cortical control of gaze.     

Claustral efferents to the cat's limbic cortex studied with retrograde and anterograde tracing techniques

The claustral projections to the cat's limbic cortex were investigated with horseradish peroxidase retrograde tracing technique and with autoradiography. Autoradiographic injections covered small portions of either the dorsal anterior claustrum or intermediate to posterior regions of the claustrum. Injections of horseradish peroxidase were made into the subicular, insular, entorhinal, prepiriform, cingulate, retrosplenial and prefrontal cortex. Both methods revealed fully consistent data for substantial claustral efferents to the cingulate, retrosplenial, entorhinal and subicular cortex. For the prepiriform cortex claustral efferents could be established unequivocally only with the horseradish peroxidase technique. Only a rather minor projection could be traced for the claustro-insular projection. Unilateral injections of horseradish peroxidase revealed the existence of a minor number of labeled claustral cells in the contralateral hemisphere for all loci except insular and prepiriform ones. Our data show that claustral cells reach the majority of the allocortical areas of the brain. They thereby confirm the view that the claustrum projects to most regions of the cortex and furthermore that a certain kind of topography exists in the claustro-cortical afferents with a minor number of claustral cells sending afferents to the contralateral cortical hemisphere. In addition, our data reveal that the distribution of claustro-cortical afferents is uneven and that the ventral claustrum (or nucleus endopiriformis) sends fibers to more cortical regions than previously assumed. It is suggested that the claustrum participates in the integration of sensory, motivational, emotional and mnemonic information via its reciprocal claustro-neocortical and its claustro-limbic connections.     

Early postnatal development of the rat corticostriatal pathway: an anterograde axonal tracing study using biocytin pellets.

The ontogenetic development of the neocortical projections to the striatum was studied in postnatal rats by sensitive anterograde tracing with biocytin. The developmental status of this mainly glutamatergic pathway is important as it plays a major role in regulation of striatal maturation and induction of excitotoxic striatal neurodegeneration resembling the type found in Huntington's disease. Biocytin pelletts were injected into the motorcortex caudal forelimb area of newborn rats and of rats aged 3, 6, 13, 27 and 61 days followed by sacrifice and visualisation of the tracer 24 h later, at P1, P7, P14, P28 and P62, respectively. Biocytin pellets were also injected into the motorcortex jaw-lip-tongue area and into the cingulate cortex of newborn and 6-day-old rats. The biocytin pellets produced intense anterograde labelling of corticofugal projection fibres from the injection sites, as well as a local Golgi-like labelling of neurons. From postnatal day 1 into adult age efferent fibres from the motorcortex caudal forelimb area displayed a progressively denser innervation of the ipsilateral and contralateral, dorsolateral striatum. The terminating fibres were most dense in the ipsilateral striatum. In the dorsolateral striatum the corticostriatal fibres displayed a patch/matrix-like arrangement from postnatal day 14 onwards. Injections into the motorcortex jaw-lip-tongue area at postnatal days 0 and 6 displayed a progressive, denser innervation of the ipsilateral and contralateral ventrolateral striatum. The cingulate corticostriatal fibre projection, was more developed at birth than the projection from the motorcortex and increased its fibre density in the ipsilateral dorsomedial striatum up to at least day 7. In conclusion: the ipsilateral corticostriatal projections from the rat motorcortex and cingulate areas are present in newborn rats. During postnatal life the pathway develops further and specialisation of the terminating fibres into a patch/matrix like arrangement can be identified by postnatal day 14.     

Early postnatal development of the rat corticostriatal pathway: an anterograde axonal tracing study using biocytin pellets

 The ontogenetic development of the neocortical projections to the striatum was studied in postnatal rats by sensitive anterograde tracing with biocytin. The developmental status of this mainly glutamatergic pathway is important as it plays a major role in regulation of striatal maturation and induction of excitotoxic striatal neurodegeneration resembling the type found in Huntington’s disease. Biocytin pelletts were injected into the motorcortex caudal forelimb area of newborn rats and of rats aged 3, 6, 13, 27 and 61 days followed by sacrifice and visualisation of the tracer 24 h later, at P1, P7, P14, P28 and P62, respectively. Biocytin pellets were also injected into the motorcortex jaw-lip-tongue area and into the cingulate cortex of newborn and 6-day-old rats. The biocytin pellets produced intense anterograde labelling of corticofugal projection fibres from the injection sites, as well as a local Golgi-like labelling of neurons. From postnatal day 1 into adult age efferent fibres from the motorcortex caudal forelimb area displayed a progressively denser innervation of the ipsilateral and contralateral, dorsolateral striatum. The terminating fibres were most dense in the ipsilateral striatum. In the dorsolateral striatum the corticostriatal fibres displayed a patch/matrix-like arrangement from postnatal day 14 onwards. Injections into the motorcortex jaw-lip-tongue area at postnatal days 0 and 6 displayed a progressive, denser innervation of the ipsilateral and contralateral ventrolateral striatum. The cingulate corticostriatal fibre projection, was more developed at birth than the projection from the motorcortex and increased its fibre density in the ipsilateral dorsomedial striatum up to at least day 7. In conclusion: the ipsilateral corticostriatal projections from the rat motorcortex and cingulate areas are present in newborn rats. During postnatal life the pathway develops further and specialisation of the terminating fibres into a patch/matrix like arrangement can be identified by postnatal day 14. Accepted: 5 January 1999     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar parafloccular corticonuclear and nucleocortical connections were studied in the cat by means of anterograde and retrograde transport of horseradish peroxidase.Previous investigations have given evidence that the cortex of the paraflocculus can be subdivided into three zones. These zones are recognized as C₂, D₁ and D₂. The material presented is compatible with the findings from previous reports with other methods that each of these zones sends its Purkinje axons to separate regions within the cerebellar nuclei. These terminal fields are the lateral part of nucleus interpositus posterior (the alleged nuclear zone C₂) and the dentate nucleus and its transition area with nucleus interpositus anterior (the supposed nuclear D zones). The parafloccular corticonuclear fibres appear to terminate along a continuous mediolateral band extending from the NL through the NL-NIA transition area into the lateral NIP. This observation is in concordance with our previous findings concerning the termination of the cerebellar corticonuclear fibres (Dietrichs and Walberg 1979, 1980; Dietrichs 1981). Within the NL and NL-NIA transition area the Purkinje axons from the ventral paraflocculus terminate ventral to those from the dorsal paraflocculus.The nucleocortical projection shows the same zonal arrangement as the corticonuclear connection, indicating the presence of a corticonuclear-nucleocortical reciprocity.The findings are discussed with reference to previous studies on the parafloccular corticonuclear and nucleocortical connections, and some comments are made concerning the cerebellar zonal subdivision of this cortical area.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar corticonuclear and nucleocortical connections of the anterior lobe were studied in the cat by means of anterograde and retrograde transport of HRP.Previous experimental studies have given evidence that the cortex of the anterior lobe can be subdivided in a mediolateral direction into seven longitudinal zones: A, B, C₁, C₂, C₃, D₁ and D₂. An analysis of the present material shows that the Purkinje axons from each cortical zone have their own terminal region within the cerebellar nuclei, and that these areas correspond to those receiving terminal corticonuclear fibres from the same zones in other parts of the cerebellum (Dietrichs and Walberg 1979, 1980). The terminal fields are the rostral part of the fastigial nucleus (the nuclear A zone), the medial nucleus interpositus anterior (the nuclear B zone), the ventromedial nucleus interpositus posterior (the nuclear C₁ zone), the dorsolateral nucleus interpositus posterior (the nuclear C₂ zone), the lateral nucleus interpositus anterior and the medial part of the transition area between the dentate nucleus and nucleus interpositus anterior (the nuclear C₃ zone), the lateral part of this transition area and the medial dentate nucleus (the nuclear D₁ zone) and the lateral part of the dentate nucleus (the nuclear D₂ zone). The nuclear zones have no sharp borders. The seven main terminal fields are connected by areas where scanty terminal fibres occur, indicatin that the Purkinje axons from each folium of the anterior lobe from medial to lateral terminate along a continuous band which loops through the cerebellar nuclei.With few exceptions the nucleocortical projection shows the same zonal arrangement as the corticonuclear, but there is in addition a weak nucleocortical connection to the anterior lobe from the middle and caudal parts of the fastigial nucleus.These and other findings are discussed with reference to previous studies on the corticonuclear and nucleocortical projections, and some comments are made concerning the zonal subdivision of the anterior lobe.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar paramedian corticonuclear and nucleocortical connections in the cat were studied by means of anterograde and retrograde transport of HRP.Previous experimental studies have given evidence that the paramedian cortex in a lateromedial direction can be subdivided, into six longitudinal zones. These are recognized as zones D₂, D₁, C₃, C₂, C₁ and B. An analysis of our material suggests that each cortical zone has its own field of termination in the cerebellar nuclei and that the Purkinje fibres from one zone have only one terminal region. The nuclear terminal areas for the fibres from the described cortical zones are the ventral nucleus lateralis (the D₂ zone), the transition area between the nucleus lateralis and nucleus interpositus anterior (the D₁ zone), the dorsolateral nucleus interpositus posterior (the C₂ zone), the ventromedial nucleus interpositus posterior (the C₁ zone), and the dorsomedial nucleus interpositus anterior (the B zone). A separate nuclear terminal region for the fibres from a cortical C₃ zone could not be positively demonstrated, but a comparison of cases makes it likeky that it is located in the transition area of nucleus lateralis and nucleus interpositus anterior, medially to the D₁ zone.The rostral folia of the paramedian lobule project more laterally in the cerebellar nuclei than do the caudal folia. Furthermore, our findings indicate that the axons of the Purkinje cells in one folium from medial to lateral terminate along a mediolateral nuclear band which loops from the dorsomedial nucleus interpositus anterior down into the ventral nucleus interpositus posterior, and from a bend in this part to the dorsal nucleus interpositus posterior, and hence into the transition zone of nucleus interpositus anterior and nucleus lateralis, from here to proceed caudally to its end.The nucleocortical projection shows with some exceptions the same zonal arrangement as the corticonuclear, but a few labelled nuclear neurons were in some cases found in the fastigial nucleus. This nucleus does not receive Purkinje axons from the paramedian lobule. This shows that although retrogradely labelled nuclear cells usually were located among or just adjacent to anterogradely filled terminal fibres, there is not a complete reciprocity in the corticonuclear and nucleocortical projections. The observations furthermore indicate that the cortical afferents terminate as mossy fibres.The advantages and problems encountered with the use of HRP as an anterograde tracer are discussed and the observations are related to previous observations on the corticonuclear and nucleocortical cerebellar projections.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar corticonuclear and nucleocortical connections of lobulus simplex, crus I and II in the cat were studied by means of anterograde and retrograde transport of HRP. Previous experimental studies give evidence that the cortex of the cerebellar hemisphere in a lateromedial direction can be subdivided into five longitudinal zones. These are recognized as zones D₂, D₁, C₃, C₂ and C₁. Our observations indicate that each cortical zone has its own field of termination in the cerebellar nuclei, and that these nuclear fields are similar to those receiving afferents from the corresponding zones within the paramedian lobule (Dietrichs and Walberg, 1979).The Purkinje axons from each folium terminate from medial to lateral along a continuous band which loops through the cerebellar nuclei from the ventromedial part of nucleus interpositus posterior to the dorsolateral part of the same nucleus, from where it proceeds into the lateral part of nucleus interpositus anterior and the transition area between nucleus interpositus anterior and the dentate nucleus, to end within the latter. In addition to this arrangement there is a rostrocaudal organization within the hemispheral cortex so that the nuclear bands receiving Purkinje axons from the rostral folia (lobulus simplex) are situated slightly ventral to those receiving terminal fibres from the middle folia (crus I), which again are situated ventral to the terminal bands for the caudal folia (crus II).The nucleocortical projection shows largely the same zonal arrangement as the corticonuclear, but labelled nuclear neurons are in some cases found bilaterally within the fastigial nucleus. This nucleus does not receive Purkinje axons from lobulus simplex, crus I and crus II.The findings are discussed with reference to previous investigations on the cerebellar corticonuclear and nucleocortical connections, and some comments are made concerning the use of HRP as an anterograde tracer.Research Fellow, The Norwegian Research Council for Science and the Humanities     

Contralateral corticofugal projections from the lateral,suprasylvian and ectosylvian gyri in the cat

Summary Contralateral corticofugal projections were investigated following multiple injections of a mixture of tritiated leucine and proline into the lateral, postlateral, suprasylvian and ectosylvian gyri of adult cats. Transported label was found in several Contralateral subcortical regions. These included the claustrum, caudate-putamen, thalamic intralaminar nuclei, pretectum, and the superior and inferior colliculi. These results show that the crossed corticofugal projections are common in the cat and are more extensive than has been previously reported.Abbreviations AC Anterior Commissure - AM Anteromedial Nucleus - AV Anteroventral Nucleus - Cd Caudate - CeM Central Medial Nucleus - CL Central Lateral Nucleus - Cl Claustrum - CM Centromedian Nucleus - GP Globus Pallidus - IC Inferior Colliculus - LD Laterodorsal Nucleus - LGd Dorsal Nucleus of the Lateral Geniculate complex - LP Lateral Posterior Nucleus - MD Mediodorsal Nucleus - MG Principal Nucleus of the Medial Geniculate complex - OT Optic Tract - Pa Anterior Pretectal Nucleus - Pl Pulvinar Nucleus - Put Putamen - Re Reuniens Nucleus - RN Red Nucleus - SC Superior Colliculus - SN Substantia Nigra - TRC Tegmental Reticular Nucleus, central division - VA Ventral Anterior Nucleus of thalamus - VB Ventrobasal Complex of thalamus - 3 Oculomotor Nucleus     

Functional roles of the lateral suprasylvian cortex in ocular near response in the cat.

The lateral suprasylvian (LS) area, an extrastriate visual area in the cat, has been suggested to play an important role in processing motion in 3-dimensional visual space. In addition, the LS area is related to all three components of the ocular near response, i.e. lens accommodation, pupillary constriction, and ocular convergence: microstimulation in this area evoked these intra- and extraocular movements, and neuronal discharges associated with these movements were also found. Anatomical pathways, direct and indirect, from this area to premotor nuclei in the brainstem are known to exist. The present paper reviews studies useful for assessing the functional roles played by the LS area in triggering and modulating component movements in the ocular near response.     

Spatial and temporal properties of neurons of the lateral suprasylvian cortex of the cat

Neurons in the posteromedial lateral suprasylvian cortex (PMLS) of cats were recorded extracellularly to investigate their response to stimulation by bars and by sinusoidal gratings. Two general types of cells were identified: those that modulated in synchrony with the passage of drifting bars and gratings and those that responded with an unmodulated increase in discharge. Both types responded to contrast reversed gratings with a modulation of activity: the cells that modulated to drifting gratings modulated to the first harmonic of contrast reversed gratings (at appropriate spatial phase and frequency), whereas those that did not modulate to drifting gratings always modulated to the second harmonic of contrast reversed gratings. No cell had a clear null point. Nearly all cells were selective for spatial frequency. The preferred frequency ranged from 0.1 to 1 cycles per degree (cpd), and selectivity bandwidths (full width at half height) were around two octaves. Preferred spatial frequency was not correlated with receptive field size, but bandwidth and receptive field size were positively correlated. Preferred spatial frequency decreased with eccentricity, at about 0.05 octaves/deg. The response of all cells increased as a function of grating contrast up to a saturation level. The contrast threshold for response to a grating of optimal parameters was approximately 1% for most cells and the saturation contrast approximately 10%. The contrast gain was approximately 25 spikes/s per log unit of contrast. All cells were tuned for temporal frequency, preferring frequencies from approximately 3 to 10 Hz, with a selectivity bandwidth approximately 2 octaves. For some cells, the spatial selectivity did not depend on the temporal frequency and vice versa. Others were spatiotemporally coupled, with the preferred temporal frequency being lower at high than at low spatial frequencies, and the preferred spatial frequency lower at high than at low temporal frequencies. Previous results showing broad velocity tuning to a bar were replicated and found to be predictable from the combined spatial and temporal tuning of PMLS cells and the Fourier spectrum of a bar. Preferred temporal frequency steadily decreased with eccentricity, at 0.025 octaves/deg. The results for PMLS cells are compared with those of other visual areas. Acuity and spatial preference and selectivity bandwidth is comparable to all areas except area 17, where they are a factor of about two higher. Temporal selectivity in PMLS is as fine as observed in other areas. The possibility that PMLS cells may be involved with motion detection and detection of motion in depth is discussed.     

The thalamo-caudate versus thalamo-cortical projections as studied in the cat with fluorescent retrograde double labeling

Summary The distribution of thalamic cells projecting to the head of the caudate and their interrelations with thalamo-cortical cells were studied in the cat with different combinations of fluorescent tracers. Injections in the head of the caudate were combined with the injections in the pericruciate, proreal, suprasylvian, anterior cingulate, occipital and ectosylvian cortices. The following results were obtained: (i) Injections in the head of the caudate resulted in retrograde labeling of thalamic cells medially and laterally to the anteromedial (AM) nucleus, and in the medioventral part of the ventral anterior (VA) nucleus. Further, labeled cells were distributed throughout the anterior intralaminar central medial (CeM), paracentral (Pc) and central lateral (CL) nuclei, and the posterior intralaminar center median-parafascicular complex (CM-Pf). Labeled cells were mainly grouped in the mediodorsal parts of the anterior intralaminar nuclei; they were also found in the more dorsal part of the mediodorsal (MD) nucleus, ventral to the thalamic paraventricular (Pv) nucleus and to the habenular complex, (ii) Thalamo-cortical and thalamo-caudate cells overlapped in the medial part of the VA; in the anterior intralaminar nuclei they were either intermingled or were distributed in separate clusters or longitudinal bands. The two cell populations also overlapped in the posterior intralaminar complex. The greatest overlap occurred with the thalamic cell population projecting to the pericruciate cortex. (iii) Thalamic cells bifurcating to the head of the caudate and to the pericruciate cortex were found lateral to the AM, within the VA, and throughout the anterior intralaminar nuclei, especially in the CeM and in the posterior part of the CL; a few branched cells were also found in the CM. Thalamic cells bifurcating to caudate and anterior suprasylvian cortex were also found in the VA. Very few cells (scattered in the anterior thalamus lateral to the AM, as well as in the CeM, Pc and CL) were found to bifurcate to the head of the caudate and the other cortical fields here examined.Supported in part by grants CNR 80.00515.04, 81.00283.04     

Thalamic and cortical projections to middle suprasylvian cortex of cats: constancy and variation

 We investigated the constancy and variability in the numbers of thalamic and cortical neurons projecting to cat middle suprasylvian (MS) visual cortex. Retrograde pathway tracers were injected at a single anatomically and physiologically defined locus in MS cortex. Counts of labeled neurons showed that the visual thalamic projections to MS cortex consistently arose from a fixed set of nuclei in relatively constant proportions. In contrast, counts of cortical neurons revealed that transcortical inputs to MS cortex were much more variable. This differential variability may be linked to the developmental program, which affords greater influence of experiential factors on cortical pathway development than on thalamocortical pathway development. These results have implications for the development of models of cerebral connectivity that include measures of pathway variability. Received: 29 March 1996 / Accepted: 3 September 1996     

Eye movement-related activities in cells of the lateral suprasylvian cortex of the cat

Investigation of eye movement-related activities and photic responsiveness using behaving cats demonstrated distinctive representations of eye movement signals in different areas of the lateral suprasylvian cortex: visual reafference in the medial bank of the middle suprasylvian sulcus and non-visual signals (proprioceptive reafference or efference copy) in the lateral bank.     

Thalamic connections of the second somatic sensory area in cats studied with anterograde and retrograde tract-tracing techniques.

The thalamic connections of the second somatosensory area in the anterior ectosylvian gyrus of cats have been investigated using the retrograde tracer horseradish peroxidase and the anterograde tracer Phaseolus vulgaris leucoagglutinin. Horseradish peroxidase was injected iontophoretically in several somatotopic zones of the second somatosensory area map of six cats. Sites of horseradish peroxidase delivery were identified preliminarily by recording with microelectrodes the responses of neurons to skin stimulation. Phaseolus vulgaris leucoagglutinin was iontophoretically injected within the ventrobasal complex (one cat) or in the posterior complex (one cat). Horseradish peroxidase injections into cytoarchitectonic area SII retrogradely labeled neurons in the ipsilateral ventrobasal complex and in the posterior complex. Counts of labeled neurons from the ipsilateral thalamus showed that the overwhelming majority of horseradish peroxidase-labeled neurons were in the ventrobasal complex (96.3-96.9%) and few were in the posterior complex (3.1-3.7%). Neurons labeled in the ventrobasal complex were observed throughout the anteroposterior extent of the nucleus, while their mediolateral distribution varied with the site of horseradish peroxidase delivery in the body map of the second somatosensory area, which indicates that the projections from the ventrobasal complex to the second somatosensory area are somatotopically organized. In the cat in which the horseradish peroxidase injection involved both the second somatosensory area proper and the second somatosensory area medial, which lies in the lower bank of suprasylvian sulcus, labeled neurons were almost as numerous in the ventrobasal complex as in the posterior complex. Phaseolus vulgaris leucoagglutinin injected in the ventrobasal complex anterogradely labeled thalamocortical fibers in the ipsilateral anterior ectosylvian gyrus. In this case, patches of labeled fibers and terminals were distributed exclusively within the cytoarchitectonic borders of the second somatosensory area proper. Labeled terminals were numerous in layer IV and lower layer III, but terminal boutons and fibers with axonal swellings, probably forming synapses en passant, were frequently observed also in layers VI and I. Injection of Phaseolus vulgaris leucoagglutinin in the posterior complex labeled thalamocortical fibers in two distinct regions in the ipsilateral anterior ectosylvian gyrus, one lying laterally and the other medially, which correspond, respectively, to the fourth somatosensory area and the second somatosensory area medial. In both areas the densest plexus of labeled fibers and axon terminals was in layer IV and lower layer III, but numerous labeled fibers and terminals were also observed in layer I. In this case, only rare fragments of labeled fibers were present in second somatosensory area proper, but no labeled terminals could be observed.     

Thalamo-cortical connections and their correlation with receptive field properties in the cat's lateral suprasylvian visual cortex

Summary Areas PMLS and PLLS of the cat's lateral suprasylvian visual cortex display an interesting global organization of local features in their single unit response properties: direction preference is centrifugally organized and velocity preference increases with eccentricity. In addition it has previously been shown that binocular interactions are strongest around the visual field center. This characterizes the LS areas as apt for the analysis of optic flow fields and for visual processing in various kinds of visuomotor tasks (Rauschecker et al. 1987). In the present study we analysed the types of input to LS from the optic chiasm, the corpus callosum and from two thalamic relay nuclei (lateral posterior and lateral geniculate) that constitute important sources of afferent information to the LS areas. We were interested in learning how the afferent (and efferent) connections between LS and these structures relate to the response properties of LS neurons. Overlap of an RF into the ipsilateral hemifield was virtually always associated with callosal input. Latency differences between responses to electrical stimulation of the optic chiasm and the thalamic sites indicated almost exclusively fast-conducting Y-input to LS. Correlation of response latencies with receptive field properties revealed the following correspondences: A positive correlation was found between LP-latency and RF-size matching the dependence of RF size on laminar origin. The type of correlation found between LP-latency and directional tuning of LS cells suggests that an interaction between thalamic and other inputs may be responsible for direction selectivity in LS. Finally, correlation of LP-latencies with centrifugal direction preference suggests that this specific property is generated by intracortical wiring rather than by thalamic input.     

The organization of serotonergic projections to cerebral cortex in primates: retrograde transport studies.

Retrograde axonal transport and immunocytochemical methods were utilized to determine the origin of serotonergic afferents to selected primary projection and association areas of cerebral cortex in macaque monkeys. After injections of Fast Blue or Diamidino Yellow in primary motor, somatosensory, or visual cortex, retrogradely labeled neurons are found in both the dorsal and median raphe nuclei. The sets of dorsal raphe neurons which innervate these cortical areas differ in their spatial distributions along the rostrocaudal axis of the brainstem; a coarse rostrocaudal topographic relationship is found between these groups of dorsal raphe neurons and their cortical targets. In contrast, neurons in the median raphe which innervate these primary projection areas are not differentially distributed along the rostrocaudal axis. However, in both the median and dorsal raphe nuclei, most neurons projecting to primary visual cortex are situated lateral to the cells which project to motor and somatosensory areas; many of these visually projecting neurons lie among the fascicles of the medial longitudinal fasciculus. For comparison with the serotonergic innervation of primary projection areas, the locations of raphe cells projecting to three areas of association cortex were examined: dorsolateral prefrontal cortex, area 5 and area 7b. Neurons projecting to each of these association areas are found throughout the dorsal and median raphe nuclei. Their distributions are similar to one another; however, more cells projecting to dorsolateral prefrontal cortex are in the rostral part of the dorsal raphe. The dorsal and median raphe neurons projecting to these association areas are intermingled with neurons projecting to motor and somatosensory cortex, but are medial to most of those projecting to visual cortex. Thus, separate cortical areas are innervated by different sets of raphe neurons; these sets partially overlap, yet differ in their rostrocaudal and mediolateral distributions. Ascending serotonergic projections to cerebral cortex form a widely distributed system which exhibits a highly intricate anatomic organization. The present observations support the hypothesis that the dorsal raphe nucleus is comprised of distinct sets of neurons whose output is distributed to multiple, interconnected cortical areas; these serotonergic projections may play a role in the coordination of excitability in functionally related areas of cortex. In contrast, the serotonergic projections arising from the median raphe appear to be more divergent and are likely to have a global influence on cortical activity. Since these individual raphe nuclei have different projection patterns, they are likely to have distinct functional roles.     

Vestibular, cochlear and trigeminal projections to the cortex in the anterior suprasylvian sulcus of the cat

1. Cats anaesthetized with chloralose were used. Potentials evoked by electrical stimulation of the vestibular, cochlear, facial, trigeminal and chorda tympani nerves were recorded with micro-electrodes in the cortex in the anterior syprasylvian sulcus.2. Negative focal potentials with a latency of 3 msec were evoked by stimulation of the contralateral and ipsilateral vestibular nerves. These potentials were located in the lower and upper banks of the sulcus at a level just caudal to the projection of the Group I muscle afferents to the lower bank.3. The cochlear projections were located mainly in the lower bank partially overlapping the vestibular and the Group I fields.4. Trigeminal responses were recorded in both banks of the sulcus but were of largest amplitude and shortest latency rostrally in the upper bank. The potentials evoked by the chorda tympani had a similar distribution but were of low amplitude.5. The hypothesis is suggested, that the cortex in the anterior suprasylvian sulcus plays a role in the orientation of the body and head towards auditory stimuli.