PROJECT SUMMARY Our relationship with the visual world is heavily dependent on our ability to receive and process light coming into the eye. A portion of that light-derived information is needed for many non-image-forming visual functions like programming our biological clocks, controlling eye movement, and influencing mood. A major region of the brain which receives this non-image-forming visual information is located in the ventral thalamus and known as the ventral lateral geniculate nucleus (vLGN). Although the vLGN has connections with downstream regions involved in important functions, including visuomotor function, circadian photoentrainment, and vestibular function, it has not been well-studied. One reason for this significant gap in knowledge is that very little is known about funda- mental characteristics of vLGN, particularly with respect to its cellular and molecular landscape, thus making it technically challenging to develop tools to answer outstanding questions about its role in visual information pro- cessing. This study is motivated by the need to characterize the molecular architecture of vLGN, and to identify the neurons which form connections with retinal fibers. This project directly aligns with the BRAIN Initiative and the NIH's Blueprint Program by expanding fundamental understanding of neuroscience using innovative re- search methods to characterize cell types in the nervous system and mapping connected neurons in the brain. The results of this work will significantly impact the field and generate a deeper understanding of a visual region of the brain which receives, processes, and transmits non-image-forming visual information.