Figure 1.

Schematic of the “running mouse” apparatus and details of light calibrations. a, Photographs of the mouse cage. Left, A mouse is seen near the water spout extending from the wall on the lower left. The black cylindrical assembly mounted above the running wheel contained an LED that provided the variable-intensity light flash (see Materials and Methods). Right, During all experiments, the mouse cage was placed inside an inverted translucent box raised slightly above the table to permit the free flow of fresh air; the box also served as a light diffuser for experiments in which the mouse was light adapted. b, Scale drawing of the running wheel and LED light source, identifying important components and distances. IR, Infrared. c, Sample calibration traces obtained with PIN photodiode located at the bottom of the wheel at the level of the mouse's eye; each trace represents one of the timed flashes delivered to the mouse's eye on different trials. d, Magnified image of a mouse eye by Remtulla and Hallett (1985), as reproduced in (Lyubarsky et al., 2004), oriented with respect to the light field as it would be for a mouse on the lowermost position of the wheel.