Figure 3. PRC shape is robust to fluctuating synaptic background activity.

A. GP model morphology and stimulation sites. The model reproduces the morphology of a GP neuron recorded in vitro, filled with biocytin, and subsequently stained. Stimuli were delivered either to the soma (S) or a distal dendritic site (DD), i.e. the distal tip of the second dendritic branch which corresponds to D2_D in our previous publication (Schultheiss et al., 2010). B. Spike frequency dependence of somatic and dendritic PRCs when the model is driven by tonic somatic applied current. B1. Single cycle somatic PRCs are type I containing a positive peak in the F1. At higher spike frequencies the positive peak in the F1 PRC is increasingly opposed by a negative peak at the same phase in the F2. B2. Single cycle dendritic PRCs are type II containing a negative early in phase (F1) for low spike frequencies which was shifted into higher order PRCs (F2) during faster spiking. C. Average somatic and distal dendritic PRCs across 100 trials with low gain (0.5 nS unitary conductance) synaptic backgrounds for spike frequencies spanning the in vivo range. Average somatic PRCs are type I (C1), whereas distal dendritic PRCs (C2) have multiple negative regions (green and blue arrowheads) that are more pronounced during slower spiking. D. Average somatic (D1) and dendritic PRCs (D2) during high input rate synaptic backgrounds. E. Average somatic (E1) and dendritic PRCs (E2) for mid-gain synaptic backgrounds (1 nS unitary conductance). As in C, green and blue arrowheads in D2 and E2 highlight negative regions in the PRC characteristic of the effect of dendritic SK. F. Average somatic (F1) and dendritic PRCs (F2) comparing the GP_base and GP_NDSK models. F1 somatic and dendritic PRCs are attenuated when dendritic SK is intact. The negative regions early in phase of the F1 and late in phase of the F2 dendritic PRC are eliminated when SK is removed from the dendrite (F2).