Heart rate as the level of stimulation is increased from that in Figure 3 (from 0.75 <i>mA</i> to 1.75 <i>mA</i>).

<p>Pronounced bradycardia is observed.</p

Model simulation under sympathetic threshold conditions whereby the direct component of the VSC is not being activated but the indirect component is being activated at higher intensity than that in Figure 7.

<p>Pronounced tachycardia is observed, similar to that seen in the experiment under moderate intensity stimulation (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g003" target="_blank">Figure 3</a>). Red bars indicate time intervals when VNS is on.</p

Average response to VNS from 7 animals that were in the conscious state.

<p>Average response to VNS from 7 animals that were in the conscious state.</p

Model simulation under baseline conditions (zero stimulation).

<p>The oscillatory pattern and the variability in that pattern is similar to that observed in the experiment (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g001" target="_blank">Figure 1</a>) and is typical at low blood demand and in the presence of low level noise within the system <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone.0114498-Kember1" target="_blank">[14]</a>. Brief intervals of resonance, whereby the oscillations are subdued, can be observed in both cases.</p

A map of neural activity (discharge) at the three levels of the neural network under the model parasympathetic threshold conditions and corresponding to the pattern of heart rate observed in Figure 9.

<p>Here the <i>direct</i> component of the VSC is stimulated, with the level of stimulation of the indirect component being maintained the same as under the sympathetic threshold conditions. The direct component of the VSC dominates, leading to the bradycardia observed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g009" target="_blank">Figure 9</a>. Legend as in the caption of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g010" target="_blank">Figure 10</a>.</p

Model simulation under subthreshold conditions whereby the direct component of the VSC is not being activated but the indirect component and therefore the local circuit elements of the neural network are being activated at low intensity.

<p>Here, as in the experiment (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g002" target="_blank">Figure 2</a>), there are no discernible changes in heart rate. Red bars indicate time intervals when VNS is on.</p

Heart rate in an anesthetized canine under baseline conditions, in the absence of VNS.

<p>Note the variations in heart rate that occur in the normal state.</p

A map of neural activity (discharge) at the three levels of the neural network under the model subthreshold conditions and corresponding to the pattern of heart rate observed in Figure 7.

<p>Legend as in the caption of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g010" target="_blank">Figure 10</a>.</p

Heart rate under moderate level stimulation (0.75 <i>mA</i>) in the same animal as in Figure 1.

<p>Pronounced tachycardia is observed.</p

Model simulation under parasympathetic threshold conditions whereby the direct component of the VSC is now being activated while the indirect component being maintained at the same activation intensity as in Figure 8.

<p>Pronounced bradycardia is observed, similar to that seen in the experiment under high intensity stimulation (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114498#pone-0114498-g004" target="_blank">Figure 4</a>). Red bars indicate time intervals when VNS is on.</p