Figure 5. Current responses of different ChR variants to naturalistic brightness modulation at different ambient intensities.

The visual stimulus (top) consisted of a naturalistic pseudo-random intensity time course spanning 2 orders of brightness magnitude. Each section of the stimulus lasted 8 seconds, then the ambient brightness level (indicated by the section number) increased by 1 log unit, and the same intensity modulation was repeated at the new level. The model was not reset at each new brightness level; the simulation of the cell's response was continuous. The traces show the current flowing into the cell through the two open states, according to Ohm's law: I = −70 mV (g ₁ O ₁+g ₂ O ₂). A-C: Current responses of cells expressing either wild-type ChR-2, Variant A, or Variant B. D-F: Current responses of cells expressing combinations of two ChR variants.