Electrically induced independent activation of the elbow flexor and extensor centers. Stimulation by continuous trains of constant current pulses at 40 Hz of the C2 segment medial to the flexor motoneuron pool induced rhythmic bursts of the elbow flexor muscle, whereas stimulation of the caudal part of the C3 segment produced rhythmic extensor bursts, all on the ipsilateral side of stimulation (I-). The flexor and extensor muscles on the contralateral limb (C-) did not respond to the stimulation. The EMG has been rectified and low-pass-filtered at 30 Hz for clarity.