Figure 3

<p>Increasing compound EPSC amplitude increases STP. For both fast and slow compound EPSCs increasing the amplitude improved STP. However, slow compounds required an ∼40% increase in amplitude to improve STP by 50%, whereas only ∼5% amplitude increase was required to achieve the same improvement with fast compound EPSCs. <i>A,B</i>, Action potential responses induced by compound EPSCs at threshold (<i>blue</i>) and suprathreshold (<i>red</i>) level. For each case in <i>A,B</i>, 10 raw data traces are shown superimposed. <i>A</i>, Action potentials induced by a compound EPSC of τ_rise/τ_decay 0.3/3 ms. Red traces are responses to stimuli with a 5% current increment above threshold level; inset shows a zoom of the tip of the trace. <i>B</i>, Spike responses induced by a compound EPSC of τ_rise/τ_decay 5/50 ms. Red traces were induced by 60% current increment stimulation over the threshold level. <i>C</i>, STP as a function of two compound EPSCs before and after increasing the compound amplitude above the initial threshold value. Each connected pair of triangles represents one cell. <i>D</i>, The percentage of improvement of STP was linearly related to the degree of EPSC amplitude increment, independently of EPSC shape (r = .68, <i>p</i> = .001). Measurements were made with EPSCs of τ_rise/τ_decay 0.3/3, 0.6/6 5/50, 5/83, 5/200 ms. <i>E</i>, The current peak amplitude at spike threshold for EPSCs with different kinetics. <i>F</i>, The total charge (open bars) and charge at spike threshold (filled bars) for EPSCs with different kinetics. High peak currents for fast EPSPs are partially due to the charging of the membrane capacitance. Charge was measured as the integral of the compound EPSC area (mean±s.e.m.; <i>n</i> = 10 cells).