Figure 7.

The four-state and six-state models simulated with ChR2-derived parameters for short-duration pulses. With the four-state photocurrents (A), the peak occurs at the end of the on-phase. This can be seen most clearly in the plot of Pulse duration vs. Time of peak (B) where all points lie on the diagonal. For the six-state photocurrents however, the peaks lag behind the end of the illumination periods slightly (D), due to the transitions to and from the model's extra intermediate states. The inactivation phases (A,D) and magnitude of the peaks (C,F) can be seen to be very similar for both models. For the six-state model, the peak-lag effect can also be observed to diminish as the pulse duration increases (E), demonstrating the practical equivalence of the two models for long stimulation periods.