Project Summary To accurately code and react to the visual environment, signals from the retina must integrate with the spatial and temporal aspects of eye and body movements. Projections from the pretectum (PT) to the pulvinar nucleus (PUL) may serve in modifying visual signals in the context of eye and/or body movements. However, the specific role of the PT in active vision has not been tested using precise circuity manipulation methods. In the mouse, projections from the PT innervate rostral regions of the PUL that are reciprocally connected to the primary visual cortex (V1). However, little is currently known regarding PT and rostral PUL circuits, or how manipulation of the PT modifies rostral PUL activity. I propose to address these gaps in knowledge via the following specific aims. Aim 1) Determine the ultrastructure, synaptic properties, and convergence patterns of layer 5 V1 and PT inputs to rostral PUL neurons using viral tracing, electron microscopy, in vitro recording, and optogenetics. Aim 2) Characterize the morphology and response properties of retinal ganglion cells that innervate PT-PUL neurons using combinations of herpes simplex virus retrograde tracing, monosynaptic rabies virus tracing, and in vitro two-photon fluorescence imaging of calcium signals. Aim 3) Determine the response properties of PT neurons and how they affect the visual response properties of rostral PUL neurons by combining in vivo recordings from the PT and PUL of awake head-fixed mice with optogenetic inhibition of PT neurons. The goal of this project is to test the overarching hypothesis that the PT modulates PUL visual signals in the context of animal movement.