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PubMed1995

Conduction velocity groups in the retino-tectal and retino-thalamic visual pathways of the pigeon (Columbia livia).

The anatomical characteristics of the avian visual system are well known. However, there are wide gaps in our knowledge with respect to the physiological characteristics of their visual system. For example, we lack both an operational identification of the different ganglion cell types present in the retinae of birds, and a description of their presumptive differential central projections. The results presented here address this latter point by classifying the conduction velocity groups of fibers present in the optic tract of the pigeon. We report the existence of at least 5 groups of axons in the optic tract of the pigeon, with conduction velocities of 22-18 m/s, 12-10 m/s, 8 m/s, 6 m/s and less than 2.5 m/s. All five groups project to the tectum but only the four fastest groups project to the dorsal thalamic complex. The homologies with the populations of retinal axons found in cats are discussed.

Animals↗
PubMed1994

A third parallel visual pathway to primate area V1.

Recent studies of the primate visual system have focused on the proposal that the perception of form and motion are processed by two parallel pathways that originate from separate populations of cells in the retina. Earlier proposals for parallel processing of visual signals identified a third pathway that could be traced from the retina to the visual cortex. This third pathway was assumed to be unimportant. A growing body of evidence suggests that this pathway to cortex is distinct anatomically, physiologically and neurochemically, and is well represented in primates. These findings raise new and interesting questions not only about the role of this pathway, but also about the intracortical integration of afferent parallel signals.

Animals↗
PubMed1989

Visual pathways to the cerebellum: segregation in the pontine nuclei of terminal fields from different visual cortical areas in the cat.

The cerebellum receives input from visual cortical areas via a relay in the pontine nuclei. We have compared the location in the pontine nuclei of terminal fields of fibres from visual areas 18 and 20, and the posteromedial lateral suprasylvian visual area. Due to individual variations in the precise location of terminal fields, comparisons were performed in individual animals. Horseradish peroxidase-wheat germ agglutinin conjugate was used as an anterograde tracer in combination with the Fink and Heimer method for visualization of anterograde degeneration. Most of the terminal fields of area 20 are widely separated from those of area 18. Fibres from the posteromedial lateral suprasylvian visual area and area 20 terminate close to each other but overlap of terminal fields is limited. Area 18 and the posteromedial area have in some places completely overlapping terminal fields; in other places, however, there is only partial overlap or complete separation. Generally, segregation of terminal fields from different areas is most pronounced in the caudal part of the recipient zone of the pontine nuclei. The terminal fields of fibres from the three cortical areas studied appear as numerous patches arranged in a complicated mosaic that tend to form concentric lamellae around the ventromedial aspect of the peduncle. Within these lamellae, area 18 projects mainly to the innermost one, area 20 to the outermost, and the posteromedial area to an intermediate lamella. Whether terminal fibres from different areas are segregated (non-overlapping) or overlapping in the pontine nuclei is of relevance for the functional organization of the cerebrocerebellar pathway. Segregation of terminal fields from different areas would mean that the areas in question influence different sets of pontocerebellar neurons and thereby relay information to the cerebellum in separate channels. Overlap of terminal fields from different areas could mean that convergence on the same pontocerebellar neurons occurs (although convergence cannot be proved with the techniques employed in this study). This study indicates that information from visual areas is relayed at least in part in separate channels from the cortex to the cerebellum.

Animals↗
PubMed1993

Monoclonal antibody labels olfactory and visual pathways in Drosophila and Apis brains.

We employed a monoclonal antibody raised against Drosophila brain homogenate for a comparative immunocytochemical analysis of visual and olfactory pathways in brains of two insect species. On Western blots of Drosophila and Apis nervous tissue, antibody fb45 recognized an antigen with an apparent molecular weight higher than 180 kD. Application of the antibody to sections of Drosophila and Apis brain stained certain interneurons which conspicuously fasciculate in common tracts or neuropilar compartments. Both in Drosophila and in Apis, the antigen was also expressed on the perineural sheath and granular cell compartments in the majority of neuronal cell bodies. The antibody stained monopolar cells in the visual system of both species, and in Apis those fibers of the anterior superior optic tract which link the medulla with the mushroom bodies. In Drosophila, bundles of Kenyon cells of the mushroom bodies were stained. In worker bees and drones, the relay neurons of the median and lateral antennoglomerular tracts were labelled. Since the recognition of the antigen does not require fixation, the antibody can be employed to label selectively living neurons in dissociated cell culture. This opens up the possibility for future functional studies on the role of the antigen in vitro.

Animals↗
PubMed1987

Growth cone morphology varies with position in the developing mouse visual pathway from retina to first targets.

We have labeled the growth cones of retinal ganglion cell axons with HRP in intact mouse embryos. This has allowed us to visualize growth cone morphology during outgrowth along an entire CNS pathway from origin to target; to ask whether growth cone forms, and thus behaviors, differ at various points along the pathway; and to study the relationships of growth cones with the cellular environment. During the major period of axon outgrowth between embryonic day (E) 12 and 15, growth cones in the optic nerve are highly elongated (up to 40 microns) and have lamellopodial expansions, but the majority lack the microspikes or filopodia characteristic of many growth cones. Within the optic chiasm (E13-15), most growth cones shorten and spread, and project several short filopodia. In the optic tract, growth cones become more slender and again lack filopodia, resembling sleeker versions of optic nerve growth cones. Near the first target region (lateral geniculate nucleus), growth cones with filopodia arise from individual axon lengths and turn medially toward the target. Within target regions, the branches of immature axon arbors are tipped by minute swellings rather than by the enlarged growth cones prevalent during outgrowth toward targets. Electron-microscopic analysis of identified labeled growth cones in the optic nerve reveal intimate interactions between growth cones and glia or other growth cones in the form of invaginating contacts. In the optic nerve, growth cones contact immature glial (neuroepithelial) cells somewhere along their length, and also envelop bundles of neurites. In the chiasm, single growth cones simultaneously relate to many different profiles. These results demonstrate that in this single pathway from origin to targets, growth cone morphology varies systematically with position along the visual pathway. During outgrowth, simple growth cones are prominent when axons follow well-defined common pathways, and more elaborate filopodial forms appear when growth cones diverge, as they turn or come to decision regions. Together with observations in vitro and in nonmammalian nervous systems in situ, these data serve as reference points for testing to what extent growth cone form reflects intrinsic factors and interactions with the environment.

Animals↗
PubMed1990

Visual pathways in elasmobranchs: organization and phylogenetic implications.

Although earlier experimental studies of the visual system in elasmobranch fishes suggested that these fishes possess fewer primary retino-recipient nuclei than other gnathostome vertebrates, recent studies utilizing more sensitive tracing methods indicate that most elasmobranch species possess ten primary retinofugal targets in addition to the optic tectum. Furthermore, many species appear to exhibit bilateral retinal projections to these nuclei. Similarly, initial claims that the organization of the visual thalamus of elasmobranchs is more primitive than that of most other gnathostomes--in that elasmobranchs possess only a single thalamic nucleus that receives both retinal and tectal inputs and that only a single thalamo-telencephalic projection exists to the telencephalon--have been refuted. Many, if not all, elasmobranchs possess a rostrally located dorsal thalamic nucleus (anterior thalamic nucleus), that receives retinal and tectal inputs and projects bilaterally to the dorsal and medial pallium, and a more caudally and dorsally located thalamic nucleus, the dorsal posterior thalamic nucleus, that receives bilateral tectal input and projects to the ventrolateral periventricular area and/or dorsal pallium of the telencephalon. Thus the thalamic organization of elasmobranch fishes is similar to that of other gnathostomes.

Animals↗
PubMed1977

The prenatal development of some of the visual pathways in the cat.

Lesions were made in the visual system in a series of cat fetuses of known gestational age, and fiber and terminal degeneration were stained by the Eager method. The times of development of the retinal projection, of the thalamcortical and corticothalamic projections of area 17 of the visual cortex, and of the intrinsic fibers in the visual cortex were examined. Enucleation of one eye resulted in degeneration being detected bilaterally in the lateral geniculate nuclei (LGN), superior colliculi (SC) and optic tracts. The optic nerves reached the optic chiasm by the thirtieth embryonic day (E30) and the optic tract connections with the LGN and SC were made by E37. The projection always appeared stronger in the contralateral LGN and SC, and the amount of degeneration increased in both sides with increasing age. A parasagittal knife cut was made in the dorsomedial crest of the visual cortex. Where the lesion passed through the cellular layers of the cortex, intrinsic fibers were cut when these were present. The deeper part of the incision through the white matter undercut the medial wall of the visual cortex, interrupting thalamocortical and corticothalamic fibers when these were present. The longer horizontal fibers that were intrinsic to the visual cortex began to develop during the last two weeks of gestation but were not fully developed at birth. In the undercut visual cortex distant from the place of entry of the lesion, and before the intrinsic fibers of the cortex had developed, degeneration was found in layers 1 and 4, demonstrating the presence of a thalamocortical pathway. The youngest fetus to show this degeneration was operated at E48. This degeneration was not present three days earlier at E45. Fiber plexuses that have been described earlier in development (Marin-Padilla, '71; Cragg, '75) do not appear to degenerate after undercutting the cortex. The corticothalamic pathway to the lateral posterior nucleus medial to the LGN was developed at E45. The descending pathways to the ipsilateral LGN and SC were developed by E48, but it is not known whether they are present before this. Thus degeneration has been used to detect the development of axonal pathways in the fetus for the first time; the major afferent and efferent pathways are developed at an earlier stage than has previously been described.

Animals↗
PubMed1987

Involvement of somatosensory and visual pathways in late onset ataxia.

Nerve conduction studies, median nerve somatosensory (SEPs) and pattern-reversal visual evoked potentials (VEPs) were recorded in 10 patients with late onset ataxia. Nine patients had dysfunction of somatosensory pathways, eight of them axonal polyneuropathy in nerve conduction measurements, and four had also impaired impulse conduction along the visual pathways. Abnormalities in records of evoked potentials occurred as prolonged latencies rather than reduced amplitudes. The observed dysfunction of peripheral and central pathways was not related to the duration or the severity of the clinical involvement by the disease. It is emphasized, however, that there seemed to be a relationship between the prolonged SEP latencies and the impaired peripheral nerve conduction values and between the diminished VEP amplitudes and the most delayed VEP latencies.

Adult↗
PubMed1991

A new anatomical representation of the human visual pathways.

A three-dimensional, computer-aided reconstruction of the intracranial parts of the visual system, optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation and striate area on the basis of anatomical serial cuts is presented in this paper. The computer-graphic representation simulates the illumination of a three-dimensional reconstruction. This study depicts for the first time a detailed anatomical reconstruction and illustrative representation of the striate area. An interactive investigation of the structure on the screen as well as a demonstration of the intracranial relationships between different neuroanatomical structures and comparisons with magnetic resonance, computed tomographic, and positron emission tomographic images is possible, providing that the neuroimaging uses the identical Cartesian coordinate system [22].

Aged↗
PubMed1996

Interaction of motion and color in the visual pathways.

In recent years the idea of parallel and independent processing streams for different visual attributes has become a guiding principle for linking the organization, architecture and function of the visual system. Findings concerning the segregation of motion and color information have been at the forefront of the evidence in favor of the parallel processing scheme. A number of studies have shown that motion perception is impaired for isoluminant stimuli, which are thought to isolate the color system. However, there are now many studies, the results of which are incompatible with the simple idea of segregated pathways. We propose two processing streams for motion that differ mostly in their temporal characteristics. Although neither of the two motion streams is color-blind, as was originally suggested, they differ radically in the way they process color information. The view that we propose provides a framework that reconciles a number of seemingly contradictory results. Evidence to support the new framework comes from psychophysical, physiological and lesion studies.

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