Vision at its sensitivity limit: Linking neural circuit function with behavior

Correlating neural circuit function with behavior is a central goal in neuroscience. This has been difficult because of the complexity of neural circuits and the computations relevant for behavior. Vision at the sensitivity limit offers an outstanding possibility to overcome these challenges. Nevertheless, it has remained unclear to which extent
the two fundamentally different retinal outputs – On and Off pathways – define behavior. We measured the sensitivity limit of light detection at the level of mouse rods, retinal ganglion cells (On and Off sustained alpha-like cells), and behavior. Responses of single rods were recorded with suction pipettes and ganglion-cell responses with patch electrodes in flat-mounted darkadapted retinas. Visually guided behavior was measured in a water maze test using a novel tracking method of mice. By manipulating single-quantum responses via transgenic techniques in a mouse line (OPN) expressing human L-cone pigment in its rods, we show that visually guided
behavior at the detection threshold relies on information provided by the retinal On pathwayHigher-order decision mechanisms cannot integrate information across On and Off retinal outputs even when it would allow higher visual sensitivity. High amplification of single-photon responses in rods and nonlinear signal processing in the On pathway are the key determinants defining behavioral threshold.