Fig. 3. Cumulative paired-pulse facilitation from an unidentified alpha lobe-extrinsic neuron (A,B) or a PE1 neuron (C). t was set to the optimal time interval of the two pulses for the induction of paired-pulse facilitation (30 ms in A, 20 ms in C). Filled circles, spike numbers elicited by the first pulse; open circles, spike numbers to the second pulse. The ordinate gives the number of spikes elicited by a single stimulus, and the abscissa time in s. In B the stimulus artefacts mark the test pulses.