The visual system not only enables us to see but also performs nonimage-forming tasks such as the pupillary light reflex, synchronization of daily (i.e. circadian) rhythms with the light/dark cycle, and regulation of hormone secretion. Nonimage-forming vision is mediated by the recently discovered intrinsically photosensitive retinal ganglion cells (ipRGCs), a subset of retinal output neurons that contains the light-sensing molecule melanopsin. My lab investigates three questions regarding ipRGC physiology:
• How do ipRGCs respond to light? Despite the functional importance of ipRGCs, their photoresponse properties remain poorly understood. Using human subjects as well as rodents, my lab is investigating how ipRGCs respond to light stimuli of various durations, intensities, wavelengths, and temporal patterns. We are also examining the molecular and cellular mechanisms underlying ipRGCs' unique light responses. The results will help develop better phototherapy for jet lag and seasonal affective disorder, and healthier electric lights at home, work and school.
• How do the various types of ipRGCs differ functionally? We recently discovered five types of ipRGCs in mice and rats. My lab is studying the five cell types' electrophysiological diversity to better understand their different functional roles.
• To what extent do ipRGCs signal to other retinal cells, and what does this signaling do? For over a century, retinal ganglion cells were thought to signal only to higher visual centers of the brain. Surprisingly, my postdoctoral work showed that ipRGCs transmit light-evoked responses to a type of retinal amacrine cells, the dopaminergic amacrine cell. My lab has identified many more types of amacrine cells to which ipRGCs signal, and is analyzing the circuits and functions of such retrograde signaling.