1,721,204 research outputs found
The postnatal development of somatosensory callosal connections after partial lesions of somatosensory areas
No full textThe distribution of S1 (first somatosensory area) and S2 (second somatosensory area) neurons projecting to the contralateral S2 was studied with horseradish peroxidase in normal adult cats and in cats aged between 129 and 248 days in which the injected S2 area had been deprived of some of its input by an earlier lesion (on postnatal days 3 to 30; day of birth = day 1) of ipsilateral S1, alone or combined with a lesion of contralateral S2. In animals with S1 lesions, as in the normal controls, labeled neurons were selectively distributed to the regions of the trunk representation and to parts of the forelimb and hindlimb representations; however, the normally acallosal region in the forepaw representation contained scattered labeled neurons in three of the four animals whose S1 had been lesioned during the first postnatal week. In these animals, the distribution of labeled neurons in the contralateral S2 was apparently normal. Furthermore, the additional lesion of this area during the first postnatal week (one animal) did not increase the degree of filling-in of the normally acallosal parts of S1. The partial filling-in of the acallosal parts of S1 is probably due to the preservation to adulthood of some of the callosal neurons which are present in these regions during the early postnatal life. Possibly, these neurons did not disappear (or lose their callosal axons) because the neonatal lesion (i) allowed their successful competition for terminal space in contralateral S2 or (ii) induced a reorganization of the peripheral input to this area
Postnatal shaping of callosal connections from sensory areas
No full textHorseradish peroxidase (HRP) was injected unilaterally into the first and second visual areas (V1 and V2; areas 17 and 18) of 20 kittens aged between 2 and 90 days and into the second somatosensory area (S2) of 16 kittens aged between 1 and 52 days. The radial and tangential (normal and parallel to the pial surface, respectively) distributions of neurons giving origin to callosal axons (callosal neurons) were studied. In adult cats, callosal efferent zones (CZs) are defined by the distribution of callosal neurons. CZs occupy, in the visual cortices, tangentially and radially restricted parts of areas 17, 18, 19 of the lateral suprasylvian gyrus and in the somatosensory cortices, parts of S1 and S2. At birth, callosal neurons are distributed throughout the tangential extent of visual and somatosensory areas; they are also more widespread in depth than in the adult. During the first postnatal month, as a result of the gradual disappearance of callosal neurons from parts of the visual and somatosensory areas, the adult CZs emerge. The CZ in areas 17 and 18 undergoes a further tangential reduction during the second and third postnatal months
The anatomical substrate of callosal messages from SI and SII in the cat
No full textHorseradish peroxidase (HRP) was injected into the first (SI) or second (SII) somatosensory areas of 21 adult cats. The radial and tangential (normal and parallel to the pial surface, respectively) distribution and morphology of the callosal neurons were studied. HRP injections were combined with single unit recording in the contralateral cortex in order to determine which part of the somatosensory periphery is represented within the regions containing callosal neurons, the callosal (efferent) zones, in SI and SII. The callosal zone of SI extends over the trunk and part of the forepaw representation. In the forepaw and hindlimb representations callosal neurons projecting only to the contralateral SII are found, while in the trunk representation callosal neurons projecting to contralateral SI or SII are found. The callosal zone in SII extends widely throughout the forepaw representation in this area and projects to the contralateral SII but not to SI. In both SI and SII the collosal neurons are mainly located in layer III. A few of them are also found in layer VI. They are very rare in other layers. Callosal neurons in layer III are mostly pyramidal but exceptionally stellate; in layer VI they are pyramidal, triangular and occasionally stellate. These data indicate that transformations of the cortical somatosensory maps are achieved in the message sent through the corpus callosum. These transformations are i) determined by the extent and location of the callosal zones and perhaps by the distribution of callosal neurons within them, ii) different in different areas, iii) different in a same area, according to the cortical targets to which they are conveyed. The existence of callosal connections originated from areas of distal forepaw representation supplied a possible anatomical substrate for those types of intermanual transfer of tactile learning which depend upon the integrity of the corpus callosum
Areal Differences in Diameter and Length of Corticofugal Projections
No full textCortical areas differ in the size and distribution of neuronal cell bodies, density, and distribution of myelinated axons, connections, and functional properties. We find that they also differ in the diameter of long corticofugal axons, with the thickest axons originating from primary motor, somatosensory, and visual areas and the thinnest ones from prefrontal and temporal areas. Since diameter is proportional to axonal conduction velocity, it can be inferred that action potentials issued from the different areas will be relayed to their targets at different speed. Conduction delays also depend on conduction distance. By computing conduction velocity and conduction distances, we found the longest conduction delays for the primary visual and temporal areas and the shortest for the premotor, primary motor, and somatosensory areas, compatible with the available electrophysiological data. These findings seem to establish a new principle in cortical organization relevant to the pathophysiology of neurological or psychiatric illnesses as well as to the speed of information processing in cortical circuits
Exuberant projection into the corpus callosum from the visual cortex of newborn cats.
No full textIn the first postnatal week, neurones projecting into the corpus callosum can be identified in kitten's visual cortex by retrograde transport of HRP. The neurones are located in layers III, IV, and VI. The region of cortex which gives rise to the callosal projection extends beyond its adult boundaries over most of area 17, 18, 19 and in the suprasylvian sulcus
The diameter of cortical axons depends both on the area of origin and target
Full text linkIn primates, different cortical areas send axons of different diameters into comparable tracts, notably the corpus callosum (Tomasi S, Caminiti R, Innocenti GM. 2012. Areal differences in diameter and length of corticofugal projections. Cereb Cortex. 22:1463-1472). We now explored if an area also sends axons of different diameters to different targets. We find that the parietal area PEc sends thicker axons to area 4 and 6, and thinner ones to the cingulate region (area 24). Areas 4 and 9, each sends axons of different diameters to the nucleus caudatus, to different levels of the internal capsule, and to the thalamus. The internal capsule receives the thickest axon, followed by thalamus and nucleus caudatus. The 2 areas (4 and 9) differ in the diameter and length of axons to corresponding targets. We calculated how diameter determines conduction velocity of the axons and together with pathway length determines transmission delays between different brain sites. We propose that projections from and within the cerebral cortex consist of a complex system of lines of communication with different geometrical and time computing properties. © The Author 2013
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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