Fig. 8.
Intracellular demonstration of E-S depression.A, Sample voltage traces from a representative experiment near threshold. Top row, fEPSPs; average of 10 consecutive responses to paired stimuli (50 msec IPI) at 260 μA (black) and then at 300 μA (gray).Bottom row, The corresponding 10 intracellular recordings at the two intensities, showing both spike-free and spike-containing EPSP–IPSP sequences. Note that the first intensity produced 3 of 10 spikes on pulse 2, and the second intensity produced 3 of 10 spikes on pulse 1, but the corresponding fEPSPs show that pulse 2 required a larger fEPSP to reach the same spike probability. B, Intracellular E-S curves for pulse 1 (open circles, gray line) and pulse 2 (filled circles, black line) from the same experiment shown inA. Note that the pulse 2 E-S curve is shifted to the right (arrow indicates E50 shift). Thedotted line passes through the points corresponding to the threshold traces shown in A. The intracellular traces at threshold are redrawn to the rightsuperimposed, to show that the second pulse reaches threshold on a larger EPSP that originates from a more hyperpolarized potential.