Fig. 6. Reduction (A,B) and enhancement (C) of tetanus-induced augmentation after repeated tetani. Both neurons were unidentified alpha lobe-extrinsic neurons. The tetani (T in A; thick vertical lines in B,C) were repeated at intervals of 1–2 min. In A,B, four tetani were applied (the second tetanus is not shown in the diagrams in B but can be seen in the spike frequency plot in A). In C, three tetani were applied. (A) Spontaneous and stimulus-induced spike frequency shown as a dot plot (instantaneous frequency). The neuron had a tendency to produce short bursts at intervals of about 10 s. This form of bursting behaviour became more prominent after the fourth tetanus. Test stimuli were given at 1 s intervals. The ordinates in B and C show the number of spikes elicited by a single stimulus, and the abscissa time in min.