Sunday, May 11, 2025
5/11/2025
An Expanded Visual Cortex for the Superior Colliculus - Project Abstract Studies of cortical visual processing in mammals have traditionally focused on the visual pathway that ascends from the retina to primary visual cortex (V1) via the lateral geniculate nucleus of the thalamus (LGN), the so-called geniculate pathway. However, visual information can also reach cortex through an alternate “extrageniculate” visual pathway in which retinal projections to the superior colliculus (SC) are relayed through the pulvinar nucleus of the thalamus (PN) before radiating to various regions of the visual cortex. While this extrageniculate pathway has been extensively characterized in primates and cats, its contribution to visually evoked activity in higher-order visual cortices is generally considered of lesser consequence than that of the geniculate pathway, at least in those higher-order visual cortices studied thus far. In the mouse, however, recent experiments from our lab have demonstrated that this extrageniculate pathway is actually the principal driver of visually evoked activity in a higher-order visual area called postrhinal cortex (POR). This discovery provides us with a well-defined system for studying the role of the extrageniculate pathway in cortical visual processing, a pathway that evolutionary neuroanatomists consider the ancestral visual input to the cortex. The mouse has about ten higher cortical visual areas whose visual response are thus far considered to largely rely on the geniculate pathway. The goal of this proposal is to use anatomical and functional approaches to determine the extent to which visual evoked responses in higher visual areas of the mouse rely on the extra-geniculate pathway. Elucidating these properties of the extrageniculate pathways to higher visual cortices of the mouse may ultimately provide a better understanding of their function in more classical mammalian models of vision, where the role of this evolutionary conserved pathway has remained somewhat elusive. Using transsynaptic viral tracing and widefield calcium imaging, I will assess the functional and anatomical characteristics of the mouse SC’s disynaptic projections to higher visual cortices via the pulvinar nucleus. I will take advantage of the unique response properties to moving visual stimuli of the SC to identify a putative set of SC-dependent higher visual cortices. Furthermore, I will compare those functional maps with the maps of the anatomical projections that disynaptically link the SC, via LP, to higher visual cortices. I will then use genetic and pharmacological tools to silence the SC and causally demonstrate the reliance of candidate cortices on this input. Finally, I will investigate a potential role of extrageniculate visual processing in discriminating between self and exogenously generated movement in the visual field. Taken together, this research will deepen our understanding of the relationship between the SC and visual cortex in the context of higher-order visual processing. The proposed experiments will provide a rich dataset from which to develop a successful doctoral dissertation under the close mentorship of world-leaders in cortical neurobiology at the University of California, San Francisco.
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