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.