Figure 7. Change in kinetics precedes the change in gain.

A. Top, input to the kinetics block u(t) consisting of brief impulses Δu added at different times relative to a change in the baseline value of u(t). Middle, impulse response F_k(t) of the kinetics block resulting from Δu at different times relative to an increase in u(t). Bottom, F_k(t) at different times relative to decrease in u(t). B. Top, Membrane potential and LNK model of an amacrine cell at a transition from 35 to 5 % contrast. Impulses Δ were added to the kinetics block input u(t) at different times separated by 10 ms relative to the contrast transition. Middle, time constant of F_k(t) at different times relative to the change in contrast. This time constant was measured as a single exponential fit to F_k(t). Bottom. Gain measured as the amplitude of F_k(t) at different times relative to the change in contrast. C. For the contrast transition shown in B, small impulses Δs were added to the stimulus s(t) and presented to the LNK model at different times separated by 10 ms relative to the contrast transition. The resulting change in the model output r′(t) averaged over many stimulus sequences of s(t) was taken as the impulse response to Δs. Top. The time to peak of the impulse response to Δs. Bottom. Amplitude (rms) of the impulse response to Δs.