Cells were typically held in current clamp mode near −60 mV with a steady holding current, and current injections were given starting 12 pA below the steady holding current, in 3-pA steps 400 ms in duration. A total of 35 depolarization steps were given. Neurons that needed more than 50 pA to be held at −60 mV were discarded from the analysis. The total number of action potentials was counted in the 35 depolarization steps, starting from the first depolarization step, which is 12 pA below the current that causes the membrane potential to be at −60 mV (this current is usually 0, unless there is some leakage current), with the last step being in a current injection of 90 pA.
