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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 73 (1988), S. 595-605 
    ISSN: 1432-1106
    Keywords: Superior colliculus ; Brain stimulation ; Orienting behavior ; Defensive behavior ; Hamster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Syrian golden hamsters were implanted with fixed or moveable stimulating electrodes aimed at the superior colliculus (SC). Behavior was observed in response to trains of 0.1 ms pulses at 200 Hz while the animals were moving freely in an open arena or in their home cages. At threshold stimulating currents, the responses consisted almost entirely of freezing or contraversive turning, which occurred in two forms: fast turns, resembling orienting movements to sunflower seeds, and slow turns that were smooth and continuous. Other responses, including head raising and lowering, ipsiversive turning and backing movements were seen occasionally. Increasing the stimulating current usually gave a variety of responses, including circling movements, prolonged freezing, ipsilateral movements and running escape behavior. The sites in SC giving freezes at threshold tended to be located superficially (SO and above), or deep (SGP and below), while sites giving turns were in the intermediate layers. Most freeze sites occurred in the rostro-medial SC that represents the upper visual field, while turn sites occurred predominantly in caudo-lateral SC. Apart from the turns, most of the stimulated responses resembled natural defensive behavior, supporting the view that SC in rodents plays a role in organizing responses to predators, as well as in orienting behavior.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 43 (1981), S. 261-269 
    ISSN: 1432-1106
    Keywords: Hamster ; Superior colliculus ; Compression ; Ganglion cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary After partial ablation of the superior colliculus (tectum) in neonatal hamsters, the whole extent of the visual field comes to be represented in a compressed map on the remaining tectal fragment. However, the total volume of tectal tissue in which retinotectal fibers arborize is less than normal. These observations suggest that the retinal ganglion cells which arborize in this reduced volume might arise throughout the whole extent of the retina but be fewer in number than normal. Alternatively, the ganglion cells which project to the tectum might be normal in number but reduced in terminal arbor size. To distinguish between these possibilities, we have used tectal injections of horseradish peroxidase to label retinal ganglion cells which project to the tectum. The numbers of labelled cells per mm2 of retina were counted in selected regions. In hamsters with small lesions, which left 80–85% of the tectum intact, the density of labelled retinal ganglion cells was normal. However, in hamsters with larger lesions, the density of labelled cells was significantly lower than normal.
    Type of Medium: Electronic Resource
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