Signal Transfer in the Tectothalamic Pathway

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DESCRIPTION (provided by the applicant): Parallel visual pathways from the retina to the cortex, via the lateral geniculate nucleus (LGN) or via the superior colliculus (SC) and pulvinar nucleus, likely serve distinct functions in the coding of form, movement, and spatial location signals. In the LGN, further segregations of anatomically and physiologically distinct visual pathways have been identified and extensively characterized. Likewise, studies in a variety of species have noted the existence of multiple pathways from the SC to the thalamus, although these pathways are largely uncharacterized, and their functions remain unknown. The tree shrew, with its expanded tectopulvinar system, is an ideal species to begin to understand how pathways from the SC influence cortical activity via their projections to the pulvinar nucleus. Previous studies characterized two distinct zones in the tree shrew pulvinar nucleus, a dorsal region (Pd) which receives diffuse convergent input from the SC and projects to the posterior temporal cortex (Tp), and a central region (Pc) which receives specific topographic projections from the SC and projects to the dorsal temporal cortex (Td). We propose to test the idea that separate tectopulvino- cortical pathways are organized to code distinct features of visual movement. To examine this hypothesis we will 1) use in vivo extracellular recordings to compare the activity of Pd and Pc neurons during the presentation a variety of computer generated stimuli designed to test responses to simple and complex visual motion 2) use in vitro whole cell recordings to compare the membrane properties of Pc and Pc neurons and their responses to stimulation of the SC, 3) use tract tracing, immunocytochemistry and electron microscopy to anatomically characterize the connections between the Pd and Pc and temporal cortex, and 4) use in vivo intrinsic optical imaging to examine temporal cortex response pattern changes following deactivation of the SC, Pd or Pc. Given the similarities between the tree shrew and primate visual pathways, the results should further our understanding of human motion processing particularly within the tectopulvinar pathway, and cortical area MT. Therefore, the proposed studies should provide information relevant to the treatment of disorders of motion processing such as dyslexia, schizophrenia, autism and Williams Syndrome. The proposed studies may also provide insight into "blindsight", the ability of some patients to detect visual motion in the absence of visual perception.