Different patterns of CPG-related modulation of polysynaptic excitation. a, EPSPs recorded in an MG motoneuron (tilted 90°) in a sham were evoked by Quad stimuli [6 p 1.8 T] at different moments in the step cycle illustrated by the rectified and filtered ENG activity of the LGS nerve. The amplitude of polysynaptic EPSPs was maximal (gray trace) when occurring during the active period of LGS (i.e., during the extension phase). b, The amplitude of polysynaptic EPSPs evoked by Pl stimulation and recorded in an FHL motoneuron (tilted 90°) from a trained cat (6 p, 1.8 T) was minimal (black trace) during the extension phase when LGS was maximally active.Mn, Motoneuron. c, Overall, the pattern of phase-dependent modulation of polysynaptic EPSPs (19 trials in 15 cells) tended to be opposite in shams and trained cats, but this difference was not statistically significant.