Fig. 9.

Activity and depth of frequency modulation as functions of accuracy demands on stepping. A–C: top panels show the mean activity of individual neurons during different ladder tasks expressed as percentages of their activity during simple locomotion. Middle panels show that for the peak activity and bottom panels show changes in the depth of modulation. A: neurons whose activity or depth of modulation increased twice: first, typically during transition from simple to ladder-18 locomotion and then again during transition from ladder-18 to ladder-12. B: neurons whose activity or depth of modulation increased only once, typically during transition from simple to ladder-18 locomotion. C: neurons whose activity or depth of modulation decreased one time, typically during transition from simple to ladder-18 locomotion. D: normalized activity (±SD) of all recorded neurons as a function of normalized cycle time. Asterisk (*) indicates statistical difference between a precise stepping condition and simple walking (P < 0.05, post hoc t-test). For example, 5 symbols over the first time bin show that the activity in all 5 accurate stepping tasks was different from simple walking.