Clustering of IPI changes and analysis as a function of the time delay and the area under the quantile-quantile plot.

<p>If the IPIs discharged during the closed-loop stimulation sessions are shorter than those of the control sessions (top-left), the area under the qqplot curve are smaller than that for the case when IPIs from the 2 sessions come from similar IPI distributions (top-right). The area values for all 22 experiments where individually plotted against the time delays (bottom). The area values were clustered in 2 groups separated by a critical delay <i>d</i> = 100 ms, cluster A (blue crosses; n = 11) containing time delays from 5 ms to 100 ms (except <i>d</i> = 70 ms which was treated as an outlier) and cluster B (red circles; n = 10) from 100 ms to 280 ms. The areas in cluster A were smaller than those of cluster B.