A frequency-dependent switch in Purkinje cell dynamics.

<p>(A) Individual PRCs (thin dashed lines) and the average PRC (thick line) of slowly firing cells (frequency<50 Hz, n = 10, black). The average PRC is independent of the phase of the brief current pulse within the ISI. (B) Individual PRCs (thin lines) and the average PRC (thick line) of rapidly firing cells (frequency>50 Hz, n = 6, red). The PRC is phase-dependent with a peak at late phases. The thin solid line is the PRC of the cell with the lowest firing frequency (55 Hz) in this group (arrows in (B–D) and shows both a peak at late phases and a plateau at early phases. (C) Peak-to-baseline ratio (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000768#s4" target="_blank">Materials and Methods</a>) plotted against firing frequency: as the frequency increases the PRC switches from phase-independent to phase-dependent. Points shown in two colors correspond to PRCs from the same cell (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000768#pcbi-1000768-g007" target="_blank">Figure 7</a> and text for more details). (D) PRCs of the two groups of cells (black: low firing rate, same data as in (A); red: high firing rate, same data as in (B) plotted on the same axes with both the phase and the phase shift of the PRC in units of time, and phases aligned with respect to the second AP in the ISI. The peaks seen at high firing rates coincide at a time of approximately –3 ms from the second spike.</p>