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  • 1
    Electronic Resource
    Electronic Resource
    Binocular depth perception mechanisms in tongue-projecting salamanders (1995)
    Springer
    Journal of comparative physiology 176 (1995), S. 365-377 
    Details
    ISSN: 1432-1351
    Keywords: Salamander ; Depth perception ; Stereopsis Optic tectum ; Visual maps
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Tongue-projecting salamanders (Bolitoglossini) combine extreme speed and high precision in prey capture. They possess all requirements for stereoscopic depth perception: frontally oriented eyes, a substantial amount of direct ipsilateral projection in addition to the contralateral one, and binocularly driven neurons. Extracellular recordings were made from retinal afferents in the tectum as well as from the somata of tectal neurons. RF-sizes of afferents and tectal neurons were determined, and the response properties of tectal neurons were tested under monocular and binocular conditions with stimuli of different size and velocity. While RF-sizes and response properties of binocular neurons during binocular and contralateral stimulation were similar, ipsilaterally stimulated neurons exhibited much smaller RFs, lower spike rates and different size preferences. Furthermore, the contralateral retinotectal projection from one eye and the ipsilateral from the other are in register. While retinal afferents are distributed linearly over the tectal surface, most tectal neurons are activated by a retinal area corresponding to the frontal visual field; this results in a magnification of this region. The two monocular receptive fields of binocular neurons exhibit zero disparities (horopter) at distances that coincide with the maximum reach of the tongue. We hypothesize that bolitoglossine salamanders (as well as amphibians in general) make use of two kinds of disparities: (1) between the maps in the left and right tectal hemisphere, coding for the lateral eccentricity of an object, and (2) between the ipsilateral and contralateral retinotectal map, coding for the distance. The presence of substantial direct ipsilateral afferents in bolitoglossine salamanders appears to be the basis for a fast computation of object distance, which is characteristic of these animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00219062
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Simulander: A neural network model for the orientation movement of salamanders (1995)
    Springer
    Journal of comparative physiology 176 (1995), S. 379-389 
    Details
    ISSN: 1432-1351
    Keywords: Neural network ; Evolution strategy ; Salamander ; Optic tectum ; Orienting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Simulander is a feedforward neural network simulating the orientation movement of salamanders. The orientation movement is part of the prey capture behavior; it is performed with the head alone. Simulander is a network which consists of 300 neurons incorporating several cytoarchitectonic and electrophysiological features of the salamander brain. The network is trained by means of an evolution strategy. Although only 100 tectum neurons with fairly large receptive fields are used (“coarse coding”), Simulander is able to localize an irregularly moving prey precisely. It is demonstrated that large receptive field neurons are important for successful prey localization. The removal of a model tectum hemisphere leads to a network which accounts for investigations made in living monocular salamanders. The model also yields an understanding of electrical stimulation experiments in toads.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00219063
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Connectivity of the salamander pretectum: an in-vitro (whole-brain) intracellular tracing study (1998)
    Springer
    Cell & tissue research 292 (1998), S. 47-56 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Plethodontids ; Urodeles ; Optic tectum ; Electrophysiology ; Biocytin ; Salamander ; Plethodon jordani ; Hydromantes genei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The amphibian optic tectum and pretectum have been analyzed in detail anatomically and physiologically, and a specific model for tecto-pretectal interaction in the context of the visual guidance of behavior has been proposed. However, anatomical evidence for this model, particularly the precise pattern of pretecto-tectal connectivity, is lacking. Therefore, we stained pretectal neurons intracellularly in an in-vitro preparation of the salamanders Plethodon jordani and Hydromantes genei. Our results demonstrate that the projections of neurons of the nucleus praetectalis profundus are divergent and widespread. Individual neurons may project divergently to telencephalic (ipsilateral amygdala and striatum), diencephalic (ipsi-and contralateral thalamus, contralateral pretectum), and mesencephalic (ipsi- and contralateral tectum and tegmentum) centers, and to the ipsi- and contralateral medulla oblongata and rostral spinal cord. The projection of pretectal cells to the optic tectum is bilateral; axonal structures do not show discernible patterns and are present in all layers of the superficial white matter. A classification of pretectal neurons on the basis of axonal termination pattern or dendritic arborization has not been possible. Our results do not support the hypothesis that a distinct class of pretectal neurons projects to a particular subset of tectal cells. Rather, the pretectum appears to influence the tectum indirectly, acting either on retinal afferents or modulating inhibitory interneurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051033
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    Paper (German National Licenses)
    Fulltext
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