Figure 7. Melanopsin is necessary for encoding high irradiances.

(A) Mean response to 2 s blue light pulses from the 40% most “sustained” and remainder 60% most “transient” Opn4 ^−/− LGN neurons (as defined by their response to bright 60 s light steps; n = 87 and 130, respectively). (B,C) Quantification of the firing rate of Opn4 ^−/− “sustained” (B) or “transient” (C) LGN cells during the first 500 ms (left) or remainder (500–2000 ms; right) of the light pulse. Symbols indicate mean ± SEM, and lines indicate mean ±95% CI of the function that best described the data. Note that, unlike Opn1mw^R “sustained” cells, both “sustained” and “transient” Opn4 ^−/− populations display sigmoidal relationships between firing rate and irradiance, which saturate above 10¹² photons/cm²/s. Data for “transient” Opn4 ^−/− cells over 500–2,000 ms of the response were not well fit by either linear or sigmoidal functions.