Figure 7.

Responses of mouse ipRGCs to flickering versus constant lights. Whole-cell current-clamp recordings were made from 11 mouse ipRGCs (seven M1 cells and four M2 cells) under conditions that preserved synaptic input. (A) Two stimuli were presented to each cell, in random order: a 12.9 log photons cm⁻² s⁻¹ light flickering at 2 Hz with a 10% duty cycle, and a steady 11.9 log photons cm⁻² s⁻¹ light with the same photon count as the flicker. All stimuli were full-field 440-nm light. (B) Representative responses from an M1 cell (1) and M2 cell (2). The insets show magnified views of the final 5 seconds of the responses. (C) Averaged data from all cells, illustrating that both ipRGC types displayed larger steady-state spiking responses to the flicker. All mouse ipRGCs spike spontaneously in the dark.³³ Thus, to quantify the light-induced spiking increase, spike rate was averaged during the 5 seconds before light onset to calculate the spontaneous spike rate and during the last 5 seconds of photostimulation to calculate the steady-state spike rate, and the former rate was subtracted from the latter rate. In the histogram, each cell's flicker-induced spike rate increase was normalized to 1. * P < 0.05. ** P < 0.01.