ISI ± SD 1000 ± 500 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 1000 ± 1000 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 1000 ± 2000 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 1500 ± 750 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 1500 ± 1500 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 1500 ± 3000 ms Unit 1* Unit 1 + 2 Unit 1 + 2 + 3 2000 ± 1000 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 2000 ± 2000 ms Unit 1* Unit 1 + 2 Unit 1 + 2 + 3 2000 ± 4000 ms Unit 1* Unit 1 + 2 Unit 1 + 2 + 3 2500 ± 1250 ms Unit 1 Unit 1 + 2 Unit 1 + 2 + 3 2500 ± 2500 ms Unit 1* Unit 1 + 2 Unit 1 + 2 + 3 2500 ± 5000 ms Unit 1 Unit 1 + 2** Unit 1 + 2 + 3 Neurons 30.5 9.8 3.3 51.4 29.3 17.1 49.1 25.4 12.4 42.4 17.4 6.8 57.1 30 15.6 70.1 49 34.2 53.4 28.3 16 68.2 45.7 31.8 70.6 47.4 34.2 46.9 23.6 11.7 70 49.9 34.7 83.2 69.5 57.2 66.6 58.4 32.3 16.5 41.5 37.5 31 42.5 40.9 29.5 52.6 41.8 27.6 37.1 43.5 36.9 27.6 38.9 41.2 41.6 44.8 35.1 29 39.7 40.1 27.3 40.1 40.2 44.6 40 28.9 27.5 37.9 41.2 15.7 25.6 32.8 21.2 10.6 40.3 30.5 5.7 23.7 25.5 7.3 23.7 32.2 4.9 34 38.2 5.4 21.1 31.7 2.2 10.1 18.6 4.9 22.3 30.1 2.7 12.4 21.1 2 10.6 19.4 7.1 25.7 31.7 2.5 10.9 19.5 1.1 4.3 8.6 6.4 0.5 13.8 30.6 1.2 8. 3 17.3 1 8.1 16.7 0.1 6.2 21 0.4 4.9 11. 9 0 1.8 5.3 0.1 4.1 14.7 0.1 2 6.2 0.2 1.8 4.6 1.1 8.6 18.1 0 1.2 4.1 0 0.5 1.1 1.7 0.1 3.5 14.7 0 0.8 6.3 0.1 1.6 6.5 0 0.6 6 0 0.5 3.5 0 0.1 0.6 0 0.6 3.4 0 0.1 0.7 0 0.9 1.4 0.1 1.7 6.8 0 0.1 0.6 0 0.1 0.4 0.7 69.5 90.2 96.7 48.6 70.7 82.9 50.9 74.6 87.6 57.6 82.6 93.2 42.9 70 84.4 29.9 51 65.8 46.6 71.7 84 31.8 54.3 68.2 29.4 52.6 65.8 53.1 76.4 88.3 30 50.1 65.3 16.8 30.5 42.8 33.4 0.67 1.6 2.5 0.35 0.7 1.09 0.39 0.81 1.38 0.52 1.21 1.96 0.36 0.77 1.25 0.23 0.43 0.66 0.38 0.79 1.27 0.25 0.48 0.72 0.21 0.44 0.67 0.43 0.89 1.46 0.24 0.43 0.65 0.11 0.22 0.32 0.4 0.1 2.2 1.9 0.2 1.1 1.3 0.1 1 1.5 0.2 1.8 2 0.3 0.8 1.1 0.3 0.3 0.7 0 0.8 0.9 0.3 0.4 0.8 0.3 0.7 1.1 0.3 1.1 1.6 0.4 0.9 1.1 0.2 0.3 0.5 2.4 Maceﬁeld Modeling human postganglionic neuronal ﬁring Table 1 | Firing patterns of model postganglionic neurons driven by 1, 2, or 3 model preganglionic neurons with differing interspike interval (ISI) distributions. 0 Spikes 1 Spike 2 Spikes 3 Spikes 4 Spikes Firing prob. Mean freq. Intervals ≤20 ms% Mean data on the percentage of cardiac intervals in which units were silent (0 spikes) or generated 1 spike, 2, 3, or 4 spikes, ﬁring probability (ﬁring prob.), and mean ﬁring rate (mean freq.). Data obtained from real muscle vasoconstrictor neurons are shown in the bottom row (data pooled from Maceﬁeld et al., 1994; Maceﬁeld and Wallin, 1999a). Asterisks indicate that for these ISI distributions the ﬁring pattern could be partially explained by a postganglionic neuron being driven by one preganglionic neuron. Bold text indicates that for this ISI distribution the ﬁring pattern closely matches that of the real sympathetic neurons. www.frontiersin.org December 2011 | Volume 5 | Article 132 | 5