Light is an important and ever present regulator of physiology and behavior, and is involved in processes as wide ranging as daily hormonal oscillations, pattern vision, sleep, attention, and circadian photoentrainment. But how are light signals relayed to the brain to mediate these complex visual behaviors? In mammals, all light information reaches the brain via projections from the retinal ganglion cells (RGCs), of which there are ~20 subtypes in the retina. Therefore, to understand how light regulates behavior, we must understand: 1) How do RGC subtypes respond to different light stimuli? 2) What are the specific cellular targets of individual RGC subtypes in the brain? and 3) What are the functional contributions of RGC subtypes to defined visual behaviors?
We study these questions by looking at the role of RGC subtypes in specific visual functions. For example, the intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin, comprise five subtypes that drive a wide range of behaviors from circadian photoentrainment to contrast sensitivity for vision. The defined and quantitative behaviors in which these cells are involved, and the myriad available genetic tools for study of this system make it an ideal one in which to study the circuitry and role of ganglion cells in visual behavior. We do this using a range of techniques from electrophysiology, neuroanatomy, and behavioral approaches in various genetic mouse models.