Figure 6. Frequency dependence of RRP size, depletion, and refilling. A, Quantum content of EPPs during trains of different frequencies [1 (black), 5 (yellow), 10 (light blue), 20 (dark blue), 50 (green), and 100 (red) Hz], each with 100 shocks, as a fraction of the largest EPP in the train. Logarithmic x-axis. B, Relative plateau values as a function of stimulation frequency. The plateau level declines steeply between 1 and 10 Hz, and then levels off, changing relatively little between 10 and 100 Hz. C, Three examples of quantum contents (1, 10, and 100 Hz trains) illustrating the tight coupling between RRP loss and recruitment, over a 100-fold range of frequency. Note the changing x-axis limits. D, The time constant of RRP loss (red) and the half-time of RRP refilling (black) are steeply dependent on stimulation frequency (x-axis) but tightly coupled. Logarithmic x-axis. E, Calculated RRP size depends on stimulation frequency, more than doubling as the frequency rises from 1 to 100 Hz. Error bars are ±1 SD.