Showing papers by "Ann M. Graybiel published in 1983"

The afferent and efferent connections of the feline nucleus tegmenti pedunculopontinus, pars compacta

Abstract: The fiber connections of the nucleus tegmenti pedunculopontinus, pars compacta (TPc) were studied by means of the anterograde autoradiographic and retrograde horseradish peroxidase tracer methods. The limits of TPc, which is not a cytoarchitecturally distinct cell group in the cat, were estimated on the basis of autoradiographic experiments in which we plotted the distribution of afferent connections from the entopeduncular nucleus, motor cortex, substantia nigra, and subthalamic nucleus. We concluded that in the cat, TPc can most readily be identified by the terminal distribution of fibers originating in the substantia nigra. Deposits of radiolabel in the motor-pre-motor cortex, the entopeduncular nucleus, and subthalamic nucleus weakly labeled the same tegmental region. Parallel horseradish peroxidase experiments suggested that neurons near the entopeduncular nucleus, especially in the lateral hypothalamus and subthalamus, contribute to the pallido-TPc pathway; that entopeduncular neurons projecting to TPc are most numerous in the ventral part of the nucleus; and that of the neocortical motor fields, both areas 4 and 6 project to TPc. An autoradiographic study of the efferent connections of TPc showed that the major connections were directed toward more rostral structures. Small deposits of labeled amino acids centered in TPc invariably elicited bilateral labeling of the pars compacta of the substantia nigra and the subthalamic nucleus, the densest label being on the ipsilateral side. Other structures variably or more sparsely labeled were: the posterior and lateral hypothalamus; centre median complex; an intermediate part of the lateral thalamic nucleus; central gray substance; nucleus parabrachialis pigmentosus (retro-rubral nucleus); the raphe nuclei linearis intermedius, dorsalis, and magnus; nucleus reticularis tegmenti pontis; the pontine and medullary reticular for-mation including the nuclei pontis oralis and caudalis; and the nucleus reticularis gigantocellularis, especially its ventral supraolivary part. These observations demonstrate that TPc shares some connections with a wider tegmental region, but that, in addition, TPc is characterized by a set of afferent and efferent connections that differentiate it from the surrounding teg-mentum and affiliate it with the basal ganglia. By comparison with findings in the monkey and rat, these experiments further suggest that the connections of TPc may vary across mammalian species. The location and fiber connections of TPc indicate that it is probably distinct from the physiologically defined mesencephalic locomotor region, but suggest the hypothesis that TPc, as a part of an extrapyramidal tegmental loop-circuit, may be involved in the production of simple resting tremors.

An outlying visual area in the cerebral cortex of the cat.

Abstract: Publisher Summary The visual cortex has been shown in both primates and non-primates to include a large number of extrastriate areas in addition to the classically defined visual areas 17, 18 and 19. Not all of these extrastriate areas contain full representations of the visual field, but, whether their maps are partial or complete, the areas abut one another, often with mirror reversals at their borders. As a consequence, the striate and extrastriate areas together form a zone of exclusive visual reponsiveness in the posterior neocortex that is continuous even though having separate areas within it. The arrangement of these visual areas into a continuum has obvious advantages in keeping transcortical association pathways short and also has suggested that the multiple maps might have evolved by a process akin to gene duplication. A visual area has been recently discovered, which appears anomalous in that it lies at a distance from the striate and extrastriate areas, in the anterior part of the cat's cerebral cortex, and yet, like the posterior visual areas, is a zone containing unimodal visually responsive neurons.

Compartmental Organization of the Mammalian Striatum

Abstract: Publisher Summary By far the most striking architectural characteristic of the mammalian cerebral hemisphere is its division into tissue of cortical and subcortical types. This distinction has dominated views about the level of sophistication and neural processing in different parts of the telencephalon, and has also influenced ideas about the evolution of the cerebral hemispheres from an apparently more primitive striatal type to the exquisitely differentiated neocortical type found in higher mammals, especially man (Herrick, 1926, 1956; Romer, 1962). Because the cerebral cortex is the largest subdivision of the human brain, and disproportionately so by comparison with other species, the view naturally arose that the specialized structure of cortex somehow forms a necessary prerequisite for the complex mental capacities unique to the human. The fact that there is very little cortical tissue in the telencephalon of non-mammalian vertebrates, but instead a large noncortical “striatal” mass, led to the parallel assumption that the striatum is the highest integrative subdivision in these forms. Thus for years it was thought that the great development of the striatum in birds was related to their highly evolved instinctive patterns of behavior. This chapter focuses on compartmental organization of the mammalian striatum.

Subsystems within the visual association cortex as delineated by their thalamic and transcortical affiliations.

Abstract: Publisher Summary Studies of the neurobiological basis of vision are being focused increasingly on the visual association cortex. This intensification of interest in the extrastriate visual areas has prompted a reexamination of fiber pathways distributing visual information to these areas and permitting interactions among them. For nearly a century, it has been recognized that the association areas receive visual signals, either directly or indirectly, from corticocortical fibers originating in the primary visual cortex. This cascade of transcortical fiber projections leading out from the striate cortex has been repeatedly confirmed with modern neuroanatomical methods and figures prominently in much of the current thinking about the processing of visual information by the forebrain. Many questions raised by the discovery of alternate ascending conduction routes have yet to be resolved. Prominent among these is how the transcortical association and ascending extrageniculate pathways are combined and integrated at the level of the visual cortex. This chapter reports here preliminary results indicating that, at least in the cat, these two sets of connections are systematically related.