Effects of Pl or LGS nerve stimulation during fictive locomotion and scratching. A–D, Top panels show ENG from extensor (LGS or MG) and flexor (TA) nerves in 2 cats with short trains of electrical stimuli to the Pl nerve (25p at 1.8T, 200 Hz) during early flexion in fictive locomotion (A) and scratching (B) and during the late extension (C) or late flexion (D) interval epochs of fictive locomotion and scratching, respectively. The onset of the flexion phase and cycle period is indicated above the TA waveform. E, F, Average phase duration of the flexion phase F1 or F2 stimulation during EF, MF, LF, and EXT or FLEX-INT epochs, expressed relative to control flexion phase durations. The duration of the extension or flexion-interval phase (i.e., between F1 and F2) is also shown. Note that when the stimuli fall in EXT or FLEX-INT the extension or flexion-interval phase is the stimulated phase. G, H, Mean flexor cycle period CPstim and CPafter stimulation measured for the same epochs as in E, F. The number of data points used in each condition to calculate phase durations and cycle periods is indicated below the epoch of G, H. Each bar is the mean ± SE. Asterisks indicate significant differences with control cycles (paired t tests). *p < 0.05, **p < 0.01, ***p < 0.01.