Fig. 8.
Roles of synaptic depression and loss of facilitation in PSP depression. A pair of pulses was presented 510 msec before the tetanus (20 Hz) (see Fig. 6), and a second pair was presented 35 msec after the tetanus (20 Hz). The PSP1/PSP2 ratio is the amplitude (in millivolts) of the PSP resulting from the first LL pulse divided by the amplitude of the PSP from the second LL pulse, delivered 35 msec after the first. PSP depression is the decline in PSP amplitude during the 1 sec duration tetanus (20 Hz). Inset, The results expected if PSP depression (top) or loss of facilitation (bottom) primarily accounts for PSP depression. Three trends are visible in the data: pretetanus PSP ratios are >1, post-tetanus values are near 1, and greater PSP depression is associated with greater paired-pulse depression.