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B Magalhães-Castro

Publications and source records attributed to B Magalhães-Castro.

11 recordsLinked to original sources
PubMed1992

Relative sizes of cortical visual areas in marmosets: functional and phylogenetic implications.

Visual areas V1, V2 and MT (V5) were identified through myeloarchitectonic criteria and their sizes estimated in a flattened map of caudal cerebral cortex in the marmoset Callithrix penicillata. The ratio MT/V1 in this species is similar to values reported for other species of primates, but the ratio V2/V1 in Callithrix penicillata is smaller than that in macaques and larger than that in Aotus. The possible implications of these results are discussed.

Animals↗
PubMed1980

Absence of tectotectal pathway in the rabbit: an anatomical and electrophysiological study.

Absence of tectotectal pathway in rabbits is demonstrated by means of anatomical (retrograde axonal transport of horseradish peroxidase (HRP)) and of physiological (electrical stimulation of the superior colliculus (SC)) methods. Despite the absence of that pathway it was still possible to verify the occurrence of electrophysiological correlates of Sprague's phenomenon. It is suggested that, in rabbits at least, reciprocal inhibitory influences between the colliculi can be mediated by pathway(s) other than the tectotectal projection. It is also hypothesized that the absence of tectotectal pathway could possibly be functionally correlated to a small degree of binocular vision and to a small representation of the ipsilateral visual hemifield in the superior colliculus.

Animals↗
PubMed1978

Horseradish peroxidase labeling of cat tectotectal cells.

By means of unilateral intracollicular injections of horseradish peroxidase (HRP), the cells of origin of the tectotectal projection in cats were detected in the opposite colliculus. The 9 injected animals were divided into two groups in accordance to the location of their injections along the collicular rostrocaudal axis. The majority of the labeled cells were obtained from two injections performed at the level of the commissure of the superior colliculus (231 cells) whereas 5 injections performed at lower levels led to labeling of 49 cells. In two animals, the injections did not cause labeling of cells, a fact that was attributed to the superficiality of the injections. Concerning the distribution of the labeled cells over the collicular layers and along the collicular rostrocaudal axis, there was no difference between the two groups of animals. Among the 280 labeled cells, 1 cell (0.35%) was found in stratum griseum superficiale, 83 cells (29.64%) in stratum opticum, 182 cells (65.00%) in stratum griseum intermediale and 14 cells (5.00%) in stratum griseum profundum. Ninety-two per cent of the cells were located in the rostral portion of the colliculus, in the region between the collicular rostral tip and the collicular rostral plane that corresponds to the vertical meridian representation. Eight per cent of the cells were concentrated in a zone comprising the lower half of stratum opticum and the upper half of stratum griseum intermediale, a location that corresponds to the transition between the visual-sensory and the visual-motor colliculus. On the basis of laminar segregation of collicular functions, the possibility that the tectotectal projection could be related to visual orienting, following and attentive collicular functions through the suppression of activity (a non-enhancement effect?) of homologous cells in the opposite colliculus is discussed.

Animals↗
PubMed1976

Cat retinal ganglion cells projecting to the superior colliculus as shown by the horseradish peroxidase method.

1. Cat retinal ganglion cells projecting to the superior colliculus (SC) were detected in flat whole-mounts of Nissl-stained retinas by means of unilateral intracollicular injections of horseradish peroxidase (HRP). 2. With the purpose of drawing a comparison between HRP-labeled ganglion cells and the remaining population of unlabeled ganglion cells, the latter were classified according to their perikaryal characteristics into three groups: large, medium and small ganglion cells. Measurements of perikaryal sizes of ganglion cells distributed from the central area to the periphery of the retina showed that large cells ranged from 20 to 44 mum, medium cells from 15 to 30 mum and small cells from 8 to 17 mum. 3. Peroxidase-labeled retinal ganglion cells (HRP-cells) occurred among representatives of each of the three groups into which retinal ganglion cells had been classified. Small HRP-cells clearly constituted the majority of the HRP-cell population. When the injection site was restricted to the superior colliculus, medium HRP-cells as large as 19 mum were only occasionally observed, the 15 to 18 mum range being predominant over the medium cell population. 4. Medium HRP-cells larger than 20 mum were a common finding only when the injection site involved the pretectal nuclei and were never observed when the injection site was restricted to superior colliculus. 5. Possibility of a correspondence between the large, medium and small HRP-cells of the present study with, respectively, the physiological types Y-, X- and W- of cat retinal ganglion cells is discussed.

Afferent Pathways↗
PubMed1976

Relationship between visual and tactile representations in cat superior colliculus.

A stratified organization of visual, somatic and acoustic representations was observed in the cat SC. Cells of the superficial laminae were exclusively visual. Visual, somatic, and acoustic cells were observed in the intermediate laminae while the deeper laminae were predominantly nonvisual. A detailed examination of the tactile representation revealed a somatotopic plan which was in register with the overlying visuotopy. The magnified representation of central visual fields overlapped the magnified tactile representation of the face and, as visual RFS moved temporally, the underlying tactile RFS were displaced caudal and distal. This topographical overlap can be recognized if the visual field is depicted as a flexible sheet which is stretched over the body with the area centralis superimposed on the nose and the limbs radiating out at an acute angle. The overlapping topographies and similarities in stimulus specificity of somatic and visual cells, as well as the similar behavioral deficits previously described following SC lesions, suggests a functional parallel between modalities in the SC. The possibility that visual, somatic, and acoustic cells converge on a common delivery or distribution system, which is located in the intermediate-deeper SC strata and organizes orienting and following responses on the basis of multimodality cues, is discussed.

Acoustic Stimulation↗
PubMed1975

Sensory and motor representation in the cerebral cortex of the three-toed sloth (Bradypus tridactylus).

Cortical sensory receiving areas were studied in 32 specimens of the three-toed sloth, Bradypus tridactylus, using the evoked response technique and barbiturate anaesthesia. Somatotopic organization in the somesthetic first area (S-I) was shown to be similar to that reported in higher mammals. The area devoted to the representation of the forelimb was considerably larger than that for the remaining body parts. The second somatosensory area (S-II), showing bilateral representation without a precise topographical organization, was identified in the rostral portion of the ectosylvian gyrus. Visual and auditory projections, occupying restricted areas, were found along the caudal banks of the ectosylvian fissure. Electrically excitable cortical motor area was explored in 8 animals anesthetized with diallyl barbituric acid in urethane. The motor representation of the various body parts was shown to coincide with the sensory projections, demonstrating the existence in a Eutherian mammal of a sensorimotor amalgam, identical to that described in marsupials. These findings suggest that sloths display a primitive pattern of neural organization, and that the sensory motor amalgam is a generalized form of cortical organization of primitive Therian mammals.

Acoustic Stimulation↗