Parallel Processing in the Visual System of Zebra Finches

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The primary visual pathway in zebra finches, termed the tectofugal pathway, travels from the retina to the optic tectum to the thalamus (n. rotundus), and then to the telencephalon (ectostriatum). Three studies were conducted to examine 1) the hodological organization of the tectofugal pathway, 2) the morphology of n. rotundus neurons, and 3) the ultrastructure of n. rotundus. In the first study, anterograde and retrograde tract-tracing substances were deposited unilaterally into n. rotundus and ectostriatum. The results showed that the dorsal-anterior, central, and posterior divisions of n. rotundus project, respectively, to the ventral-anterior, central, and dorsal-posterior regions of the ectostriatum. In the second study, cell bodies from different anatomical subdivisions of n. rotundus were analyzed to identify possible morphological differences. The results showed that cells in the dorsal-anterior and central division are larger than those in the posterior region. In the third study, tissues of n. rotundus were examined with a transmission electron microscope. The results showed that all subdivisions of n. rotundus are primarily composed of asymmetric membrane specializations with clear, rounded synaptic vesicles. However, synaptic glomeruli are more prominent in the central and posterior divisions of n. rotundus. Taken together, the present results are reminiscent of the findings in mammals, in which the primary visual system consists of parallel processing pathways that differ in anatomical, morphological, and ultrastructural characteristics. Thus, birds may process visual information in a manner similar to mammals, namely through parallel processing visual channels. Supported by: University of South Florida and NSF

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Vision Sciences Society, v. 2, issue 7, art. 103