Spontaneous firing activities in IC neurons. A: Representative FRA showing typical spontaneous firing. B: A typical spontaneous firing curve over time in an IC neuron. C: The percentage of neurons with spontaneous firing activity in normal (114 neurons from 6 animals), short recovery (161 neurons from 7 animals) and long recovery groups (74 neuron from 6 animals). *Significant difference from normal group (P < 0.05).