Fig. 11.

Representation of LP waveforms and PD gIPSPs with equivalent rectangles. The equivalent rectangle of a waveform is defined as a rectangle of length t_equiv(a measure of the waveform length) and heightV_avg (a measure of the average amplitude of the waveform), in which t_equiv is twice the time that divides the waveform in two parts with equal integrals, andV_avg is the ratio of the integral of the waveform in one period to t_equiv. The area of the equivalent rectangle is therefore equal to the integral of the waveform during one cycle. A, Equivalent rectangles superimposed on one cycle of a 0.2 Hz LP waveform (bottom) and the PD response (top). The integral of the LP waveform is measured from its minimum, and the integral of the PD response is measured from its baseline (−23 mV). Vertical bar, 2 mV (PD) and 20 mV (LP). B, Equivalent rectangles for LP waveforms (bottom) and PD responses (top, mean ± SEM; n = 14) at frequencies of 0.2, 0.8, 2.0, and 2.8 Hz. In each case, two duty cycles are superimposed: 55/45 (light gray) and 35/65 (dark gray). The height of the equivalent rectangles for PD responses are V_avg values normalized to the V_avg of the response to the 0.1 Hz LP waveform with the duty cycle of 55/45 (A_ref). Vertical bar,A_ref (PD) and 40 mV (LP). C,V_avg normalized byA_ref (mean ± SEM;n = 14) plotted against frequency for gIPSPs in response to LP waveforms with duty cycles of 55/45 (open circles) and 35/65 (filled circles).D, t_equiv normalized by period (mean ± SEM; n = 13) plotted against frequency for gIPSPs in response to LP waveforms with duty cycles of 55/45 (open circles) and 35/65 (filled circles). Dotted lines show the normalizedt_equiv values for the LP waveforms (0.41 for the 35/65 duty cycle and 0.61 for the 55/45 duty cycle).