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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↗
PubMed2002

Cortical synaptic arrangements of the third visual pathway in three primate species: Macaca mulatta, Saimiri sciureus, and Aotus trivirgatus.

The koniocellular (K) pathway is one of three pathways from the lateral geniculate nucleus (LGN) to primate visual cortex (V1). K pathway projections to the cytochrome oxidase (CO) blobs of V1 suggest involvement in chromatic processing given reports that the CO blobs in diurnal primates contain cells selective for color. K LGN layers and CO blobs, however, are also well developed in nocturnal primates such as owl monkeys, which are likely to be color blind. Thus, the K pathway plays either different roles in different species or some as yet unidentified common role(s). Because synaptic arrangements underlie functional mechanisms, the purpose of this investigation was to compare the synaptic circuitry related to the K pathway within the CO blobs of two diurnal primates (macaque monkeys and squirrel monkeys) and one nocturnal primate (owl monkey). Presynaptic K axons were labeled with wheat germ agglutinin-HRP, and presynaptic and postsynaptic profiles in CO blobs were identified with post-embedding immunocytochemistry for GABA and glutamate. In all three species, K axon terminals are glutamatergic and larger than local axon terminals, suggesting that they have a greater impact on postsynaptic CO blob targets than signals arriving via layer IV from the P or M pathways. A greater proportion of K axons, however, synapse with larger glutamatergic shafts in the diurnal monkeys than in the nocturnal owl monkey, perhaps reflecting the importance of color within the K pathway of these diurnal species. Alternatively, the loss of color vision in the owl monkey could impact K pathway circuitry earlier in the pathway. The basic similarities between K axon circuitry within the CO blobs of the three primate species examined also could indicate that this pathway plays some common role or roles across species.

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↗
PubMed2003

Temporal dynamics of binocular disparity processing in the central visual pathway.

To solve the stereo correspondence problem (i.e., find the matching features of a visual scene in both eyes), it is advantageous to combine information across spatial scales. The details of how this is accomplished are not clear. Psychophysical studies and mathematical models have suggested various types of interactions across spatial scale, including coarse to fine, fine to coarse, averaging, and population coding. In this study, we investigate dynamic changes in disparity tuning of simple and complex cells in the cat's striate cortex over a short time span. We find that disparity frequency increases and disparity ranges decrease while optimal disparity remains constant, and this conforms to a coarse-to-fine mechanism. We explore the origin of this mechanism by examining the frequency and size dynamics exhibited by binocular simple cells and neurons in the lateral geniculate nucleus (LGN). The results suggest a strong role for a feed-forward mechanism, which could originate in the retina. However, we find that the dynamic changes seen in the disparity range of simple cells cannot be predicted from their left and right eye monocular receptive field (RF) size changes. This discrepancy suggests the possibility of a dynamic nonlinearity or disparity specific feedback that alters tuning or a combination of both mechanisms.

Animals↗
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.

Color↗
PubMed2003

Age-related changes in the dynamics of human albino visual pathways.

A deficiency of melanin in the retinal pigment epithelium, which regulates the development of neural retina, leads to chiasmal misrouting such that the uncrossed pathway (to the ipsilateral hemisphere) is reduced relative to the crossed pathway (to the contralateral hemisphere). This study examines age-related changes in the flash and pattern appearance visual evoked potentials (VEP) of human albinos. Scalp recorded cortical VEPs to flash (FVEP) and pattern appearance stimulation were recorded in 58 albino (8 months to 60 years) and 34 normal subjects (4-55 years). VEPs were analysed by amplitude and latency. The contralateral hemisphere FVEP amplitude decreased with age in albino subjects, as in both hemispheres in normals. However, the ipsilateral hemisphere FVEP amplitude was significantly lower in young albino subjects, initially giving a marked interhemispheric asymmetry, but this normalized with age. Significant interhemispheric FVEP latency asymmetries were not observed. The contralateral pattern appearance VEP latency in albino subjects decreased with age, as in both hemispheres in normals; the ipsilateral latency increased significantly with age. Significant interhemispheric pattern appearance VEP amplitude asymmetries were not observed. These novel and unexpected observations indicate significant age-related changes in the retinocortical pathways of the human albino. These changes have implications for our understanding of development and plasticity of the central visual pathways.

Adolescent↗
PubMed2002

Electrophysiology of the postreceptoral visual pathway in mice.

Pattern VEPs have been recorded locally from the binocular portion of the primary visual cortex of wild type- and different transgenic mice by means of microelectrodes. Local pattern VEPs have been used on the one hand to obtain information on basic cortical layout (topography, laminar analysis) and ocularity (relative contribution of the contralateral and ipsilateral eye), and on the other hand to evaluate several aspects of visual physiology that have a counterpart in visual behavior (visual acuity, contrast sensitivity, motion sensitivity, response latency). As compared to visual behavior, pattern VEPs offer the advantage that several aspects of vision can be evaluated in the same animals, including those with poor behavior due to motor- or cognitive deficits, even during the postnatal development. Pattern VEPs provide a means for characterizing the visual phenotype of mutant mice and for the evaluation of the effects induced by experimental manipulation.

Animals↗