The Organization of the Tectofugal Visual Pathway in the Zebra Finch

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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). The purpose of the present study was to examine the thalamo-telencephalic organization of the tectofugal pathway in zebra finches by using tract-tracing methods. Anterograde and retrograde anatomical tracers (i.e., 10K MW biotinylated dextran amine and cholera toxin subunit B, respectively) were deposited unilaterally into n.rotundus and the ectostriatum. Immunohistochemical and/or avidin-biotin/DAB procedures were used to visualize the tracer injections and the resulting labeling patterns. The results showed that at least two anatomically distinct subdivisions of n. rotundus project to different subdivisions of the ectostriatum. In particular, the dorsal-anterior division of n. rotundus projects exclusively to the ventral-anterior region of the ectostriatum, whereas the rest of n. rotundus (i.e., the central and posterior subdivisions) send topographically organized projections to the rest of the ectostriatum. These results indicate that the thalamo-telencephalic division of the tectofugal pathway contains at least two anatomically distinct processing streams. The present results are reminiscent of the findings in primates, in which the primary visual pathway consists of parallel processing streams that differ in anatomical, physiological, neurochemical, and functional characteristics (e.g., Merigan and Maunsell, 1993). Thus, birds may process visual information in a manner similar to primates, namely through parallel processing visual channels.

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Society for Neuroscience Abstracts, v. 27, p 855.21