Organization of neural inputs to the suprachiasmatic nucleus in the rat

The circadian timing of the suprachiasmatic nucleus (SCN) is modulated by its neural inputs. In the present study, we examine the organization of the neural inputs to the rat SCN using both retrograde and anterograde tracing methods. After Fluoro-Gold injections into the SCN, retrogradely labeled neurons are present in a number of brain areas, including the infralimbic cortex, the lateral septum, the medial preoptic area, the subfornical organ, the paraventricular thalamus, the subparaventricular zone, the ventromedial hypothalamic nucleus, the posterior hypothalamic area, the intergeniculate leaflet, the olivary pretectal nucleus, the ventral subiculum, and the median raphe nuclei. In the anterograde tracing experiments, we observe three patterns of afferent termination within the SCN that correspond to the photic/raphe, limbic/hypothalamic, and thalamic inputs. The median raphe projection to the SCN terminates densely within the ventral subdivision and sparsely within the dorsal subdivision. Similarly, areas that receive photic input, such as the retina, the intergeniculate leaflet, and the pretectal area, densely innervate the ventral SCN but provide only minor innervation of the dorsal SCN. A complementary pattern of axonal labeling, with labeled fibers concentrated in the dorsal SCN, is observed after anterograde tracer injections into the hypothalamus and into limbic areas, such as the ventral subiculum and infralimbic cortex. A third, less common pattern of labeling, exemplified by the paraventricular thalamic afferents, consists of diffuse axonal labeling throughout the SCN. Our results show that the SCN afferent connections are topographically organized. These hodological differences may reflect a functional heterogeneity within the SCN.     

Extrastriate feedback to primary visual cortex in primates: a quantitative analysis of connectivity

Knowledge-based or top-down influences on primary visual cortex (area V1) are believed to originate from information conveyed by extrastriate feedback axon connections. Understanding how this information is communicated to area V1 neurons relies in part on elucidating the quantitative as well as the qualitative nature of extrastriate pathway connectivity. A quantitative analysis of the connectivity based on anatomical data regarding the feedback pathway from extrastriate area V2 to area V1 in macaque monkey suggests (i) a total of around ten million or more area V2 axons project to area V1; (ii) the mean number of synaptic inputs from area V2 per upper-layer pyramidal cell in area V1 is less than 6% of all excitatory inputs; and (iii) the mean degree of convergence of area V2 afferents may be high, perhaps more than 100 afferent axons per cell. These results are consistent with empirical observations of the density of radial myelinated axons present in the upper layers in macaque area V1 and the proportion of excitatory extrastriate feedback synaptic inputs onto upper-layer neurons in rat visual cortex. Thus, in primate area V1, extrastriate feedback synapses onto upper-layer cells may, like geniculocortical afferent synapses onto layer IVC neurons, form only a small percentage of the total excitatory synaptic input.     

Widespread origin of the primate mesofrontal dopamine system

The dopaminergic innervation of the frontal cortex, commonly implicated in psychiatric and neurological disorders, has traditionally been associated with a circumscribed midline group of ventral tegmental area (VTA) neurons. We have employed a combination of retrograde tracing, using fluorescent dyes, and tyrosine hydroxylase (TH) immunohistochemistry to amplify knowledge of frontal cortex-projecting dopamine (DA) neurons in non-human primates. Injections of retrograde fluorochromes were made in areas 46, 8B/6M, 12, 4, 24, and the prelimbic (PL) and infralimbic areas (IL) of the rhesus monkey. The mesencephalic distribution of neurons exhibiting both retrograde labeling and TH immunoreactivity or retrograde labeling alone was examined from the level of the mammillary bodies to the locus coeruleus. DA afferents innervating the macaque frontal cortex as a whole originate from an unexpectedly widespread continuum of neurons distributed in the dorsal aspects of all three of the mesencephalic DA cell groups [A9, A10 and A8; generally corresponding to the DA cells of the substantia nigra (SN), VTA, and the retrorubral area (RRA) respectively]. A large number of these retrogradely labeled neurons are non-dopaminergic. The dorsal frontal cortex (areas 46, BB/6M and 4) receive DA projections primarily from the full medial-lateral extent of A9 cells dorsal to the SN pars compacta (i.e. A9 dorsalis), the RRA and to a lesser extent from the A10 parabrachial pigmented nucleus (PBPG) and linear nuclei, the latter of which have been associated with the mesocortical DA system. In contrast, the ventromedial PL and IL exhibit a significantly more robust input from the PBPG and midline linear VTA nuclei than from the lateral groups. The anterior cingulate cortex (area 24) is innervated by a group of DA neurons primarily located between these laterally and medially concentrated populations. These findings demonstrate a degree of compartmentalization of the mesofrontal DA system in primates, and suggest that this projection should no longer be viewed as a unitary midline system.     

Promoter/repressor system of Lactobacillus plantarum phage og1e: characterization of the promoters pR49-pR-pL and overproduction of the cro-like protein cng in Escherichia coli

Previous studies have shown that extensive damage to the medial prefrontal cortex (mPFC) of rats causes reversal learning deficits. The mPFC of rats, however, consists of several subareas that are different from each other in both cytoarchitecture and neural connectivity, suggesting a functional dissociation among the mPFC subareas. In the present study, selective lesions of the mPFC of rats were made with a specially designed microknife whose intracranial placement could be controlled stereotaxically. Restricted lesions were made to each of the 3 parts of the mPFC: the anterior cingulate area (AC) (including the medial precentral area, PrCm), the prelimbic area (PL), and the infralimbic area (IL). One week after surgery, rats were trained in an aversively motivated visual discrimination task in a novel rotating T-maze. After reaching the acquisition criterion, rats were trained in a reversal task in the same maze. No difference was found in acquisition between control and mPFC lesioned rats. However, lesions of either the PL or the IL produced a marked deficit in the reversal task. This behavioral deficit was not found in rats with lesions of the AC. The results indicate that the mPFC of rats is not essential for discrimination learning, but that each of the 2 ventral subareas of the mPFC, PL, and IL, plays a critical role in reversal learning.     

Neuroendocrine tumors of the lung. Pathology and molecular biology

The cortical connections of visual area 3 (V3) and the ventral posterior area (VP) in the macaque monkey were studied by using combinations of retrograde and anterograde tracers. Tracer injections were made into V3 or VP following electrophysiological recording in and near the target area. The pattern of ipsilateral cortical connections was analyzed in relation to the pattern of interhemispheric connections identified after transection of the corpus callosum. Both V3 and VP have major connections with areas V2, V3A, posterior intraparietal area (PIP), V4, middle temporal area (MT), medial superior temporal area (dorsal) (MSTd), and ventral intraparietal area (VIP). Their connections differ in several respects. Specifically, V3 has connections with areas V1 and V4 transitional area (V4t) that are absent for VP; VP has connections with areas ventral occipitotemporal area (VOT), dorsal prelunate area (DP), and visually responsive portion of temporal visual area F (VTF) that are absent or occur only rarely for V3. The laminar pattern of labelled terminals and retrogradely labeled cell bodies allowed assessment of the hierarchical relationships between areas V3 and VP and their various targets. Areas V1 and V2 are at a lower level than V3 and VP; all of the remaining areas are at a higher level. V3 receives major inputs from layer 4B of V1, suggesting an association with the magnocellular-dominated processing stream and a role in routing magnocellular-dominated information along pathways leading to both parietal and temporal lobes. The convergence and divergence of pathways involving V3 and VP underscores the distributed nature of hierarchical processing in the visual system.     

The ipsilateral and contralateral connections of the fifth somatosensory area (SV) in the cat cerebral cortex

THE ipsilateral and contralateral corticocortical connections to the fifth somatosensory area (SV) in the feline cortex were determined from the location of retrogradely labelled cells following a single injection of HRP into SV. The injection was made into physiologically defined components of the body representation in SV. After injection of HRP into the face regions of SV, HRP-labelled cells were located ipsilaterally in areas 6 beta, 3b and 1-2 of the primary somatosensory (SI), in the second somatosensory (SII), third somatosensory (SIII), and fourth somatosensory (SIV) areas, along the ansate sulcus, and in areas 5a and 6a beta of the ipsilateral cortex, as well as in area 1-2 of SI and in SV of the contralateral cortex. On the other hand, after HRP had been injected into the trunk/hindlimb area, HRP-labelled cells were located in areas 3a, 1-2 of SI, in area 5, in SII, in SIII and in SIV of the ipsilateral cortex, as well as in area 1-2 of SI, and in SV of the contralateral cortex. The extent of these interconnections suggests that SV receives multiple sensory inputs and may function to integrate this information.     

Fluorescence cross-correlation: a new concept for polymerase chain reaction

Infusion of sodium selenite to the occipital cortex of the rat was used for the specific tracing of zinc-rich pathways. Large numbers of labeled somata were found ipsilaterally in the visual, orbital and frontal cortices, and contralaterally in homotopic and heterotopic visual areas. Labeled neurons were also found ipsilaterally in the retrosplenial, parietal, sensory-motor, temporal and perirhinal cortex. In contrast to the cortico-cortical connections, ascending afferents to the visual cortex were not zinc-rich except for a few labeled neurons in the claustrum. Additional injections showed reciprocal zinc-rich connections between the visual cortex and the orbital and frontal cortices. The latter cortices also received ascending zinc-rich afferents from the claustrum. Selenite injections revealed the layered distribution and the morphology of these labeled neurons in the neocortex. Zinc-rich neurons were found in layers II-III, V and VI. However, none was found in layer IV. Zinc-rich somata appeared as pyramidal and inverted neurons. The contrasting chemical properties of cortical and subcortical visual afferents may account for the functional differences between these systems.     

Prefrontal connections of the parabelt auditory cortex in macaque monkeys

In the present study, we determined connections of three newly defined regions of auditory cortex with regions of the frontal lobe, and how two of these regions in the frontal lobe interconnect and connect to other portions of frontal cortex and the temporal lobe in macaque monkeys. We conceptualize auditory cortex as including a core of primary areas, a surrounding belt of auditory areas, a lateral parabelt of two divisions, and adjoining regions of temporal cortex with parabelt connections. Injections of several different fluorescent tracers and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were placed in caudal (CPB) and rostral (RPB) divisions of the parabelt, and in cortex of the superior temporal gyrus rostral to the parabelt with parabelt connections (STGr). Injections were also placed in two regions of the frontal lobe that were labeled by a parabelt injection in the same case. The results lead to several major conclusions. First, CPB injections label many neurons in dorsal prearcuate cortex in the region of the frontal eye field and neurons in dorsal prefrontal cortex of the principal sulcus, but few or no neurons in orbitofrontal cortex. Fine-grain label in these same regions as a result of a WGA-HRP injection suggests that the connections are reciprocal. Second, RPB injections label overlapping prearcuate and principal sulcus locations, as well as more rostral cortex of the principal sulcus, and several locations in orbitofrontal cortex. Third, STGr injections label locations in orbitofrontal cortex, some of which overlap those of RPB injections, but not prearcuate or principal sulcus locations. Fourth, injections in prearcuate and principal sulcus locations labeled by a CPB injection labeled neurons in CPB and RPB, with little involvement of the auditory belt and no involvement of the core. In addition, the results indicated that the two frontal lobe regions are densely interconnected. They also connect with largely separate regions of the frontal pole and more medial premotor and dorsal prefrontal cortex, but not with the extensive orbitofrontal region which has RPB and STGr connections. The results suggest that both RPB and CPB provide the major auditory connections with the region related to directing eye movements towards stimuli of interest, and the dorsal prefrontal cortex for working memory. Other auditory connections to these regions of the frontal lobe appear to be minor. RPB has connections with orbitofrontal cortex, important in psychosocial and emotional functions, while STGr primarily connects with orbital and polar prefrontal cortex.     

Projections from the presubiculum and the parasubiculum to morphologically characterized entorhinal-hippocampal projection neurons in the rat

The relations between the inputs from the presubiculum and the parasubiculum and the cells in the entorhinal cortex that give rise to the perforant pathway have been studied in the rat at the light microscopical level. Projections from the presubiculum and the parasubiculum were labeled anterogradely, and, in the same animal, cells in the entorhinal cortex that project to the hippocampal formation were labeled by retrograde tracing and subsequent intracellular filling with Lucifer Yellow. The distribution and the number of appositions between the afferent fibers and hippocampal-projection neurons in the various layers of the entorhinal cortex were analyzed. The results show that layers I-IV of the entorhinal cortex contain neurons that give rise to projections to the hippocampal formation. The morphology of these projection neurons is highly variable and afferents from the presubiculum and the parasubiculum do not show a preference for any specific morphological cell type. Both inputs preferentially innervate the dendrites of their target cells. However, presubicular and parasubicular projections differ with respect to the layer of entorhinal cortex they project to. The number of appositions of presubicular afferents with cells that have their cell bodies in layer III of the entorhinal cortex is 2-3 times higher than with cells in layer II. In contrast, afferents from the parasubiculum form at least 2-3 times as many synapses on the dendrites of cells located in layer II than on neurons that have their cell bodies in layer III. Cells in layers I and IV of the entorhinal cortex receive weak inputs from the presubiculum and parasubiculum. Not only is the presubiculum different from the parasubiculum with respect to the distribution of projections to the entorhinal cortex, they also differ in their afferent and efferent connections. In turn, cells in layer II of the entorhinal cortex differ in their electrophysiological characteristics from those in layer III. Moreover, layer II neurons give rise to the projections to the dentate gyrus and field CA3/CA2 of the hippocampus proper, and cells in layer III project to field CA1 and the subiculum. Therefore, we propose that the interactions of the entorhinal-hippocampal network with the presubiculum are different from those with the parasubiculum.     

Short-latency synaptic patterns among cat peroneal motoneurons

Motoneurons innervating peroneal muscles in the cat leg (PB, PT and PL, respectively, for peroneus brevis, tertius and longus) were examined for their connections with afferents from these and other leg muscles and with cutaneous afferents. The aim was to investigate (1) whether inputs from nearby muscles and cutaneous areas are likely to assist or oppose the excitation elicited in peroneal motoneurons by PB contractions, and (2) whether reflex connectivity might allow distinction of alpha (i.e. motoneurons innervating skeletal muscle fibres) and beta (i.e. motoneurons innervating both skeletal and intrafusal muscle fibres) subgroups among PB and PT motoneurons. In the three peroneal pools, every motoneuron had excitatory monosynaptic connections with Ia afferents from each of the three peroneal muscles, and nearly every motoneuron received di- or trisynaptic excitation from low-threshold cutaneous afferents in sural or superficial peroneal nerves. Inputs from these sources might facilitate the contraction-induced positive feedback. In contrast, the patterns of short-latency synaptic connections with group I afferents from pretibial flexor and post-tibial extensor muscles were heterogeneous among peroneal motoneurons but did not point to any specific beta pattern.     

Cortical connections of the frontoparietal opercular areas in the rhesus monkey

The connections of the frontoparietal opercular areas were studied in rhesus monkeys by using antero- and retrograde tracer techniques. The rostral opercular cortex including the gustatory and proisocortical motor (ProM) areas is connected with precentral areas 3, 1, and 2 as well as with the rostral portion of the opercular area which resembles the second somatosensory type of cortex (area SII) and the ventral portion of area 6. Its distant connections are with the ventral portion of prefrontal areas 46, 11, 12, and 13 as well as with the rostral insula and cingulate motor area (CMAr). The mid opercular region (areas 1 and 2) is connected with pre- and postcentral areas 3, 1, and 2 as well as SII. Additionally, it is connected with the ventral portion of area 6, area 44, area ProM, the gustatory area, and the rostral insula. Its distant connections are with area 4, the ventral portion of area 46, area 7b, and area POa in the intraparietal sulcus (IPS). The rostral parietal opercular region is connected with the postcentral portions of areas 3, 1, and 2; areas 5, 7, and SII; the gustatory area; and the vestibular area. Its other connections are with area 4, area 44, the ventral portion of area 46, area ProM, CMAr, and the supplementary motor area (SMA). The caudal opercular region is connected with the dorsal portion of area 3; areas 2, 5, and 7a; and areas PEa as well as IPd of IPS. It is also connected with area SII, insula, and the superior temporal sulcus. Its distant connections are with area 44; the dorsal portion of area 8 and the ventral portion of area 46; as well as CMAr, SMA, and the supplementary sensory area. This connectivity suggests that the ventral somatosensory areas are involved in sensorimotor activities mainly related to head, neck, and face structures as well as to taste. Additionally, these areas may have a role in frontal (working) and temporal (tactile) memory systems.     

A visuo-somatomotor pathway through superior parietal cortex in the macaque monkey: cortical connections of areas V6 and V6A

This report addresses the connectivity of the cortex occupying middle to dorsal levels of the anterior bank of the parieto-occipital sulcus in the macaque monkey. We have previously referred to this territory, whose perimeter is roughly circumscribed by the distribution of interhemispheric callosal fibres, as area V6, or the 'V6 complex'. Following injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA-HRP) into this region, we examined the laminar organization of labelled cells and axonal terminals to attain indications of relative hierarchical status among the network of connected areas. A notable transition in the laminar patterns of the local, intrinsic connections prompted a sub-designation of the V6 complex itself into two separate areas, V6 and V6A, with area V6A lying dorsal, or dorsomedial to V6 proper. V6 receives ascending input from V2 and V3, ranks equal to V3A and V5, and provides an ascending input to V6A at the level above. V6A is not connected to area V2 and in general is less heavily linked to the earliest visual areas; in other respects, the two parts of the V6 complex share similar spheres of connectivity. These include regions of peripheral representation in prestriate areas V3, V3A and V5, parietal visual areas V5A/MST and 7a, other regions of visuo-somatosensory association cortex within the intraparietal sulcus and on the medial surface of the hemisphere, and the premotor cortex. Subcortical connections include the medial and lateral pulvinar, caudate nucleus, claustrum, middle and deep layers of the superior colliculus and pontine nuclei. From this pattern of connections, it is clear that the V6 complex is heavily engaged in sensory-motor integration. The specific somatotopic locations within sensorimotor cortex that receive this input suggest a role in controlling the trunk and limbs, and outward reaching arm movements. There is a secondary contribution to the brain's complex oculomotor circuitry. That the medial region of the cortex is devoted to tightly interconnected representations of the sensory periphery, both visual and somatotopic-which are routinely stimulated in concert-would appear to be an aspect of the global organization of the cortex which must facilitate multimodal integration.     

Organization of the visual reticular thalamic nucleus of the rat

The visual sector of the reticular thalamic nucleus has come under some intense scrutiny over recent years, principally because of the key role that the nucleus plays in the processing of visual information. Despite this scrutiny, we know very little of how the connections between the reticular nucleus and the different areas of visual cortex and the different visual dorsal thalamic nuclei are organized. This study examines the patterns of reticular connections with the visual cortex and the dorsal thalamus in the rat, a species where the visual pathways have been well documented. Biotinylated dextran, an anterograde and retrograde tracer, was injected into different visual cortical areas [17; rostral 18a: presumed area AL: (anterolateral); caudal 18a: presumed area LM (lateromedial); rostral 18b: presumed area AM (anteromedial); caudal 18b: presumed area PM (posteromedial)] and into different visual dorsal thalamic nuclei (posterior thalamic, lateral geniculate nuclei), and the patterns of anterograde and retrograde labelling in the reticular nucleus were examined. From the cortical injections, we find that the visual sector of the reticular nucleus is divided into subsectors that each receive an input from a distinct visual cortical area, with little or no overlap. Further, the resulting pattern of cortical terminations in the reticular nucleus reflects largely the patterns of termination in the dorsal thalamus. That is, each cortical area projects to a largely distinct subsector of the reticular nucleus, as it does to a largely distinct dorsal thalamic nucleus. As with each of the visual cortical areas, each of the visual dorsal thalamic (lateral geniculate, lateral posterior, posterior thalamic) nuclei relate to a separate territory of the reticular nucleus, with little or no overlap. Each of these dorsal thalamic territories within the reticular nucleus receives inputs from one or more of the visual cortical areas. For instance, the region to the reticular nucleus that is labelled after an injection into the lateral geniculate nucleus encompasses the reticular regions which receive afferents from cortical areas 17, rostral 18b and caudal 18b. These results suggest that individual cortical areas may influence the activity of different dorsal thalamic nuclei through their reticular connections.     

Cortical afferents of the perirhinal, postrhinal, and entorhinal cortices of the rat

We have divided the cortical regions surrounding the rat hippocampus into three cytoarchitectonically discrete cortical regions, the perirhinal, the postrhinal, and the entorhinal cortices. These regions appear to be homologous to the monkey perirhinal, parahippocampal, and entorhinal cortices, respectively. The origin of cortical afferents to these regions is well-documented in the monkey but less is known about them in the rat. The present study investigated the origins of cortical input to the rat perirhinal (areas 35 and 36) and postrhinal cortices and the lateral and medial subdivisions of the entorhinal cortex (LEA and MEA) by placing injections of retrograde tracers at several locations within each region. For each experiment, the total numbers of retrogradely labeled cells (and cell densities) were estimated for 34 cortical regions. We found that the complement of cortical inputs differs for each of the five regions. Area 35 receives its heaviest input from entorhinal, piriform, and insular areas. Area 36 receives its heaviest projections from other temporal cortical regions such as ventral temporal association cortex. Area 36 also receives substantial input from insular and entorhinal areas. Whereas area 36 receives similar magnitudes of input from cortices subserving all sensory modalities, the heaviest projections to the postrhinal cortex originate in visual associational cortex and visuospatial areas such as the posterior parietal cortex. The cortical projections to the LEA are heavier than to the MEA and differ in origin. The LEA is primarily innervated by the perirhinal, insular, piriform, and postrhinal cortices. The MEA is primarily innervated by the piriform and postrhinal cortices, but also receives minor projections from retrosplenial, posterior parietal, and visual association areas.     

Receptive-field properties and neuronal connectivity in striate and parastriate cortex of contour-deprived cats

An attempt was made to relate the alterations of cortical receptive fields as they result from binocular visual deprivation to changes in afferent, intrinsic, and efferent connections of the striate and parastriate cortex. The experiments were performed in cats aged at least 1 jr with their eyelids sutured closed from birth. The results of the receptive-field analysis in A17 confirmed the reduction of light-responsive cells, the occasional incongruity of receptive-field properties in the two eyes, and to some extent also the loss of orientation and direction selectivity as reported previously. Other properties common to numerous deprived receptive fields were the lack of sharp inhibitory sidebands and the sometimes exceedingly large size of the receptive fields. Qualitatively as well as quantitatively, similar alterations were observed in area 18. A rather high percentage of cells in both areas had, however, preserved at least some orientation preference, and a few receptive fields had tuning properties comparable to those in normal cats. The ability of area 18 cells in normal cats to respond to much higher stimulus velocities than area 17 cells was not influenced by deprivation. The results obtained with electrical stimulation suggest two main deprivation effects: 1) A marked decrease in the safety factor of retinothalamic and thalamocortical transmission. 2) A clear decrease in efficiency of intracortical inhibition. But the electrical stimulation data also show that none of the basic principles of afferent, intrinsic, and efferent connectivity is lost or changed by deprivation. The conduction velocities in the subcortical afferents and the differentiation of the afferents to areas 17 and 18 into slow- and fast-conducting projection systems remain unaltered. Intrinsic excitatory connections remain functional; this is also true for the disynaptic inhibitory pathways activated preferentially by the fast-conducting thalamocortical projection. The laminar distribution of cells with monosynaptic versus polsynaptic excitatory connections is similar to that in normal cats. Neurons with corticofugal axons remain functionally connected and show the same connectivity pattern as those in normal cats. The nonspecific activation system from the mesencephalic reticular formation also remains functioning both at the thalamic and the cortical level. We conclude from these and several other observations that most, if not all, afferent, intrinsic, and efferent connections of areas 17 and 18 are specified from birth and depend only little on visual experience. This predetermined structural plan, however, allows for some freedom in the domain of orientation tuning, binocular correspondence, and retinotopy which is specified only when visual experience is possible.     

Contributions of the subregions of the medial prefrontal cortex to negative occasion setting.

The medial prefrontal cortex of rats has a role in many aspects of cognitive function, including forms of inhibitory learning. Recent studies suggest that there is heterogeneity in the contributions of the prelimbic (PL) and infralimbic (IL) regions of the medial prefrontal cortex to response inhibition. The present study tested the effects of separate neurotoxic lesions of the PL or IL on a serial feature negative discrimination task (negative occasion setting). Rats received training sessions consisting of 16 trials: on 4 trials in each session, a tone was presented and followed by food reward; on the other 12 trials the tone was preceded by a visual stimulus and not reinforced. The results indicate that PL but not IL is necessary for learning the discrimination. We then tested the effects of these lesions on rats that were first extensively trained in the task. Rats that had been trained for 30 days before receiving PL or IL lesions were still able to perform the task as well as controls after surgery. Thus, PL lesions disrupt acquisition but not performance of a serial feature negative discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Topographic organization of medial pulvinar connections with the prefrontal cortex in the rhesus monkey

The medial nucleus of the pulvinar complex (PM) has widespread connections with association cortex. We investigated the connections of the PM with the prefrontal cortex (PFC) in macaque monkeys, with tracers placed into the PM and the PFC, respectively. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) placed into the PM resulted in widespread anterograde terminal labeling in layers III and IV, and retrograde cellular labeling in layer VI of the PFC. Injections of tracers centered on the central/lateral PM resulted in labeling of dorsolateral and orbital regions, whereas injections centered on caudal, medial PM resulted in labeling of dorsomedial and medial PFC. Since injections of the PM included neighboring thalamic nuclei, retrograde tracers were placed into distinct cytoarchitectonic regions of the PFC and retrogradely labeled cells in the posterior thalamus were charted. The results of this series of tracer injections confirmed the results of thalamic injections. Injections placed into areas 8a, 12 (lateral and orbital), 45, 46 and 11, retrogradely labeled neurons in the central/lateral PM, while tracer injections placed into areas 9, 12 (lateral), 10 and 24, labeled medial PM. The connections of the PM with temporal, parietal, insular, and cingulate cortices were also examined. The central/lateral PM has reciprocal connections with posterior parietal areas 7a, 7ip, and 7b, insular cortex, caudal superior temporal sulcus (STS), caudal superior temporal gyrus (STG), and posterior cingulate, whereas medial PM is connected mainly with the anterior STS and STG, as well as the cingulate cortex and the amygdala. These connectional studies suggest that the central/ lateral and medial PM have divergent connections which may be the substrate for distinct functional circuits.     

Subdivisions of auditory cortex and levels of processing in primates

In a series of experiments on New World and Old World monkeys, architectonic features of auditory cortex were related to tone frequency maps and patterns of connections to generate and evaluate theories of cortical organization. The results suggest that cortical processing of auditory information involves a number of functionally distinct fields that can be broadly grouped into four or more levels of processing. At the first level, there are three primary-like areas, each with a discrete pattern of tonotopic organization, koniocortical histological features, and direct inputs from the ventral division of the medial geniculate complex. These three core areas are interconnected and project to a narrow surrounding belt of perhaps seven areas which receive thalamic input from the major divisions of the medial geniculate complex, the suprageniculate/limitans complex, and the medial pulvinar. The belt areas connect with a lateral parabelt region of two or more fields that are almost devoid of direct connections with the core and the ventral division of the medial geniculate complex. The parabelt fields connect with more distant cortex in the superior temporal gyrus, superior temporal sulcus, and prefrontal cortex. The results indicate that auditory processing involves 15 or more cortical areas, each of which is interconnected with a number of other fields, especially adjoining fields of the same level.     

Organizing principles of cortical integration in the rat neostriatum: corticostriate map of the body surface is an ordered lattice of curved laminae and radial points

The neuroanatomic organizing principles underlying integrative functions in the striatum are only partially understood. Within the three major subdivisions of the striatum-sensorimotor, associative, and limbic--longitudinal zones of axonal plexuses from the cerebral cortex end in bands and clusters that innervate cell groups. To identify organizing principles of the corticostriate bands and clusters, we localized somatosensory cortical cells receptive to light touch on the hindlimb, forelimb, or vibrissae by extracellular recording, and we labeled their projections by iontophoretic application of dextran anterograde tracers. The results show that cortical cells in columnar groups project to the striatum in the form of successive strips, or laminae, that parallel the curve of the external capsule. The vibrissae somatosensory cortex projects to the most lateral lamina. Just medial to the vibrissae projection, the major axonal arborizations arising from hindlimb and forelimb somatosensory cortex are organized within a common lamina, where they interdigitate and overlap as well as remain separate. In addition, the hindlimb and forelimb cortex send small projections to the vibrissae lamina, and vice versa, forming broken, radially oriented lines of points across the laminar strips. The major somatosensory projections are in the dorsolateral, calbindin-poor sensorimotor striatum, whereas the radially oriented projection points extend into the medial, calbindin-rich associative striatum. Extending previous studies of corticostriate projections, this report shows a grid translation of columnar somatosensory cortical inputs into striatum and a detailed map for the rat sensorimotor zone. The lattice-like grid is a novel functional/neuroanatomic organization that is ideal for distributing, combining, and integrating information for sensorimotor and cognitive processing.     

Interhemispheric connections of somatosensory cortex in the flying fox

The interhemispheric connections of somatosensory cortex in the gray-headed flying fox (Pteropus poliocephalus) were examined. Injections of anatomical tracers were placed into five electrophysiologically identified somatosensory areas: the primary somatosensory area (SI or area 3b), the anterior parietal areas 3a and 1/2, and the lateral somatosensory areas SII (the secondary somatosensory area) and PV (pairetal ventral area). In two animals, the hemisphere opposite to that containing the injection sites was explored electrophysiologically to allow the details of the topography of interconnections to be assessed. Examination of the areal distribution of labeled cell bodies and/or axon terminals in cortex sectioned tangential to the pial surface revealed several consistent findings. First, the density of connections varied as a function of the body part representation injected. For example, the area 3b representation of the trunk and structures of the face are more densely interconnected than the representation of distal body parts (e.g., digit 1, D1). Second, callosal connections appear to be both matched and mismatched to the body part representations injected in the opposite hemisphere. For example, an injection of retrograde tracer into the trunk representation of area 3b revealed connections from the trunk representation in the opposite hemisphere, as well as from shoulder and forelimb/wing representations. Third, the same body part is differentially connected in different fields via the corpus callosum. For example, the D1 representation in area 3b in one hemisphere had no connections with the area 3b D1 representation in the opposite hemisphere, whereas the D1 representation in area 1/2 had relatively dense reciprocal connections with area 1/2 in the opposite hemisphere. Finally, there are callosal projections to fields other than the homotopic, contralateral field. For example, the D1 representation in area 1/2 projects to contralateral area 1/2, and also to area 3b and SII.