Figure 5. Peristimulus time histogram (PSTH) vs. peristimulus frequencygram (PSF) in representing the underlying synaptic potential. The PSTH (upper trace) and PSF (lower trace) produced by an EPSP. The dashed line in both traces is the estimated EPSP produced by the current transient injected into a rat hypoglossal motoneuron in a slice preparation. The PSTH exhibited a peak during the rising phase of the EPSP, followed by a trough. Note that following the increase in firing probability during the rising phase of the EPSP, two more peaks appeared in the PSTH, denoted by two pairs of vertical lines to the right of time zero. Looking at the PSTH alone, one would have to say that there was a series of excitations followed by inhibitions. On the other hand, the increase in discharge frequency in the PSF followed the time course of the EPSP correctly, indicating that there is only one long-lasting excitatory event occurring in the motoneuron. The three horizontal lines in the PSF record represent the mean background discharge rate calculated over negative time lags (solid line) ± 2 SD (dotted lines). There were 198 stimuli. Adapted from Türker and Powers (1999) with permission from the American Physiological Society.