Spiking behaviors of ipRGCs. *A*: representative spiking responses of five ipRGCs to 1-s depolarizing current steps of various amplitudes. For each cell, an appropriate holding current was injected to maintain the baseline membrane potential at −83 ± 5 mV. The number under each response trace indicates the amplitude of the depolarizing current step. *B*: peak firing rates, calculated from the interval between the first and second spikes in the response to each current step. For individual data points in the M1 plot, *n* ranged from 8 cells to 17 cells; M2, *n* = 22 to 27; M3, *n* = 5 to 6; M4, *n* = 9 to 13; M5, *n* = 1 to 3. *C*: the highest peak firing rates of the five ipRGC types that were induced by currents up to 425 pA in amplitude. *N* values: M1, 17; M2, 27; M3, 6; M4, 13; M5, 3. *D*: average spike frequencies, measured by counting the number of spikes induced by each 1-s depolarizing current step. The *n* values are M1, 11 to 17; M2, 15 to 24; M3, 5 to 6; M4, 12 to 13; M5, 2 to 4. *E*: the highest average firing rates of the five cell types that were induced by currents up to 425 pA in amplitude. *N* values: M1, 17; M2, 24; M3, 6; M4, 13; M5, 4. *F*: spike timing regularity, quantified as the standard deviation of the interspike intervals (ISI). *N* values are the same as for *D. G*: representative spike waveforms of the five ipRGC types. *H*: the half-height spike widths of the five ipRGC types. For M1, *n* = 25 cells; M2, *n* = 53; M3, *n* = 9; M4, *n* = 22; M5, *n* = 2. *I*: measurement of the spike threshold. *J*: mean spike thresholds. For M1, *n* = 22 cells; M2, *n* = 52; M3, *n* = 10; M4, *n* = 33; M5, *n* = 3.

## PubMed Commons