Figure 7. Effects of an IPSP on motoneuron discharge probability and rate. The PSTH (upper trace) and PSF (lower trace) produced by an IPSP (dashed trace). Note that following the decrease in firing probability during the falling phase of the IPSP, three peaks appeared in the PSTH, denoted by three pairs of vertical lines to the right of time zero. The PSF produced by the same IPSP showed that the deepest part of the IPSP induced a gap in the PSF which was followed by a lower-frequency discharge during the rising phase of the IPSP. Looking at the PSTH alone, one would have to say that there was a series of inhibitions followed by excitations. The discharge rate of the PSF, however, did not change much after the initial reduction, indicating that there was only one inhibitory event. There were 198 stimuli. Adapted from Türker and Powers (1999) with permission from the American Physiological Society.