Fig. 4.

Recordings of an OFF-unit descending propriospinal interneuron during 4 cycles of rostral scratch in the D₃–D₁₀ preparation. Top trace, descending propriospinal interneurons; vertical lines in 2nd trace represent the timing of action potentials in the OFF-unit, the largest unit in top trace. The end phase of the OFF-unit was near the start phases of knee-extensor motor activities. The first cycle ends with a hip-extensor deletion variation of rostral scratch with no quiescence between 2 successive hip-flexor bursts. The other 3 cycles are normal rostral scratch cycles with hip-flexor bursts alternating with hip-flexor quiescence. The OFF-unit is active during the initial portion of each hip-flexor burst in all 4 cycles.