Noisy map based on the PRC accounts for the tight synchrony near the causal limit.

<p>Histograms from the hybrid circuit shown in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002306#pcbi-1002306-g003" target="_blank">Fig. 3B2</a> with a delay of 40 ms (A1) and in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002306#pcbi-1002306-g003" target="_blank">Fig. 3B3</a> with a delay of 50 ms (B1), relative to an intrinsic period of about 70 ms. Histogram peaks for the synchronous mode at the longer delay are much narrower than for the antiphase mode. Histograms were also generated by a noisy map based on a hypothesized circuit composition of two cells with Type II PRCs as in (C). For a normalized delay of 0.55 a histogram with two wide peaks (A2) corresponding to an antiphase mode results. As the normalized delay is increased to 0.9, an abrupt transition to synchrony with a much narrower peak (B2) is observed. C. The locking point for antiphase (filled circle marked A) falls in a much noisier region of the PRC than the locking point for synchrony (open circle marked B). The dashed line indicates the causal limit.