Integration of visual information and behavioral modulation in the superior colliculus

PROJECT SUMMARY (See instructions): Distinct visual features are extracted in parallel to be later combined and modulated along the visual pathways. Two parallel pathways can be found early on, with projections from the retina targeting the dorsal lateral geniculate nucleus, which targets cortical areas, and the superior colliculus (SC), which projects to the pulvinar among other structures. These two pathways are often referred to as the primary and the secondary pathway respectively and are inter-connected, notably at the level of the SC. Importantly, visual inputs in the SC converge onto one morphologically and molecularly defined cell type: the wide-field vertical cells (WFV). WFV cells dendritic arborizations sample a large part of the visual field and we have recently shown that these cells are modulated by locomotion and receive inputs from multiple brain region. Their morphology and projection to the pulvinar are conserved across species. These observations place WFV cells as key integrators of visual and non-visual information. To understand how WFV cells integrate information, the investigator will perform causal experiments in which different sources of inputs will be manipulated in mice (Mus musculus) while the activity of WFV cells will be assessed using calcium imaging. This will be followed by the identification of the connectivity of the WFV in another animal model, the tree shrew (Tupaia belangerii), which is highly visual and closely related to primates. This will address the conservation of the brain-wide circuit across species, thus opening new alleys for translational work. To resolve existing discrepancy concerning the overall visual responses in the SC, the visual responses of WFV cells will be characterized in tree shrews. This particular cell-type will be isolated using an optogenetic approach and electrophysiological recordings, thus allowing for the characterization of visual response preference of these cells. This project will yield compelling results regarding the integration of visual information across the visual system, allow a direct comparison of the same defined cell-type across two species, and reveal how internal states shape visual responses in the SC.