Interaction between homosynaptic postburst depression and transient heterosynaptic depression. A, Simultaneous homo- and heterosynaptic conditioning (3-impulses, 50 Hz) does not produce more depression than homosynaptic conditioning alone. Left panel shows fESPS recordings of homosynaptic conditioning alone (upper, black trace) and of simultaneous homo- and hetersosynaptic conditioning (lower, red and black trace), calibration bar 100 ms, 200 μV. Right panel summarizes the change in depression by adding heterosynaptic conditioning for three experiments (open squares). The mean change is indicated by the closed square. B, Effect of sequential hetero- and homosynaptic conditioning. Left upper panel shows fEPSP recordings of homosynaptic conditioning alone (upper, black trace) and of sequential heterosynaptic - homosynaptic conditioning (lower, red and black trace, 500 ms between conditioning stimuli; hetero- and homosynaptic conditioning indicated in red and black, respectively), calibration bar 100 ms, 100 μV. C, The left panel illustrates, for eight experiments, the depression induced by homosynaptic conditioning alone, heterosynaptic conditioning alone and sequential hetero- and homosynaptic conditioning. The corresponding changes in paired-pulse ratio are shown in the right panel.