Figure 7.
Gain control makes gap junctions less effective during the falling phase of the response to moving stimuli. A, A paired extracellular recording from neighboring coupled DSGCs reveals the window of coincident activation during the responses to moving stimuli. Note that in the overlapping region when both cells are active (highlighted in gray), C1 is able to prime C2, but C2 does not prime C1, giving rise to a skewed response. B, The spiking ON waveform measured in a coupled DSGC (blue; raw spike traces are shown in black) is compared with its excitatory synaptic inputs (red; VHOLD approximately −60 mV; these recordings were made in succession from the same DSGC). C, A plot of the spike rate versus the current for the rising (red) and decaying (blue) phases of the responses shown in B reveal a dynamic change in the spike–current relationship during the light response (the current at half-maximum response during rising phase was 88 ± 22 pA, compared with 193 ± 36 pA during the falling phase; n = 7, p = 0.029). D, The average apparent spike threshold (i.e., the amplitude of the synaptic EPSC at the point of the first and last spikes in the spike train) is plotted for the rising and decaying response phases of ON responses for both coupled (n = 7) and uncoupled (n = 6) DSGCs responding to a 300 × 300 μm bar (96% Weber contrast) moving at 600 μm/s in the preferred direction. *p < 0.05.