Fig. 7. Intraburst spike frequency, intraburst spike number, and cycle period code for different aspects of cpv1b contractions in a single experiment. A–C, Intraburst spike frequency (left column) best codes for average (A), total (B), and tonic (C) amplitudes (boxes). D, Intraburst spike number (middle column) best codes for phasic amplitude (box). Period seems to code reasonably well for phasic amplitude (right column) (R2 = 0.54), but there is large scatter around the best fit line, and points representing the same spike number (numbers on plot) have similar amplitudes despite their different periods (fine lines). Spike number is a function of cycle period, and this interdependence can produce misleading apparent correlations (see Results). E, Cycle period (right column) best codes for percent phasic (box). Again, the interdependence of spike number and period makes it appear that spike number also codes reasonably well for percent phasic (R2 = 0.72). However, there is large scatter around the best fit line, and points representing the same period (numbers on plot) have similar amplitudes despite their different spike numbers (fine lines; see Results). Open circles, solid lines, andupper R2 values are data from late in the trains; x points, dashed lines, and lower R2 values (only in boxed plots) are data from 20 sec in the train; note that in all cases the data from both sets well predict the variable in question. When 20 sec data are plotted versus the other, poorly predicting parameters, the same pattern of scatter and similar R2 values are observed as with the later data (data not shown).