A&B. Under current-clamp conditions, long (A) and short (B) laser pulses induce depolarization mixed with IPSPs in small DCN cells, where the IPSPs, but not the depolarizations, are sensitive to the GABAa receptor blocker bicuculline. C. Under voltage clamp and in the presence of bicuculline, photostimulation of varying durations induces inward currents that typically include phasic and plateau components. D. A brief laser pulse at constant intensity induces current responses that vary in size by discrete steps, suggesting a unitary response at this synapse. E. A typical type II DCN cell, showing that 1 ms laser pulses induce depolarization, but rarely spiking.