Figure 3.

Distal dendritic excitation increases action potential variability. A, Modeling excitation as a conductance source does not alter rate enhancement. Dendritic voltage records (Dend V_m; 710 μm from soma) generated in response to somatic excitation alone (top trace) or by somatic plus dendritic excitation are shown. Somatically recorded action potentials (APs) are shown as vertical lines, and the current delivered by the dynamic clamp is shown below (g_clamp). B, Summary data describing the percentage enhancement of action potential firing rate as a function of the frequency of dendritic excitation when modeled as a conductance source and delivered at proximal (301 ± 10 μm; n = 7; open symbols) or distal (607 ± 19 μm; n = 10; filled symbols) loci. C, The coefficient of variation of action potential firing is enhanced by distal but not proximal dendritic excitation. D, Proximal excitation does not change the pattern of action potential generation. Cumulative probability distribution of instantaneous (Inst.) firing frequency under the indicated experimental conditions. E, Distal excitation increased the proportion of action potentials generated at high instantaneous firing frequencies, an effect that is vetoed by synaptic inhibition (g_GABA). Error bars represent SEM. Dend, Dendritic.