FIGURE 4.

Return of excitation with increase in pulse duration. (Upper box) The cell shown was stimulated successively with three S1 pulses of 50, 55, and 50 V/cm. The cell was excited with the 50 V/cm pulses, but not with the 55 V/cm pulse. The time bar on the right applies to all three sets of recordings. (Lower box) With S1 amplitude fixed at 55 V/cm, the S1 amplitude was increased from 0.5 ms to 1 ms, 5 ms, and 10 ms. The cell did not fire an action potential for the 0.5 ms and 1 ms pulses but fired for the 5 ms and 10 ms pulses. Note the delay in excitation for the 5 ms pulse. The circled numbers indicate sequence of stimulation. The recordings corresponding to sites 1 and 8 have also been numbered in each set of traces.