PROJECT SUMMARY Intrinsically photosensitive retinal ganglion cells (ipRGCs) are neurons of the mammalian eye that capture light with a molecule called melanopsin, triggering a phototransduction cascade to generate an electrical response. This response influences dozens of brain regions and is essential for light’s normal regulation of processes that include the circadian clock, sleep, mood, and pupil constriction. Our preliminary experiments reveal ipRGC response features that are suited to these processes and qualitatively distinct from those of the classic rod and cone photoreceptors. We propose to characterize these response features, learn how they arise from molecular mechanisms within ipRGCs, and define how they shape signals sent from ipRGCs to the brain. We will apply patch-clamp electrophysiological recording to the ex vivo mouse retina and its isolated cells, introducing methods that increase the physiological relevance of our findings. Our experiments will strengthen the basic understanding of ipRGCs, sensory transduction, and ion channels. They will also provide insight into the broad question of how cells of particular types are tailored to specific tasks.