Locomotion in the cat : a behavioural and neurophysiological study of interlimb coordination

The alternating periods of flexion and extension movements at the different joints farm the elements of the locomotor cycle, which may be adapted in force and timing to satisfy the requirements for support of the body, balance and direction of progression. These basic elements of movement are produced by the activities of interneurones and moteneurones lying in the respective spinal segments innervating each limb. In his study of narcosis progression in the cat Brown (20) suggested that the flexion and extension movernents were generated by groups of rieurones driving the respective motoneurons. These groups were organized into functional half eentres producing the signals necessary for the flexion and extension phases of stepping by virtue of mutual inhibition. The existence of half eentres received some confirmatien by Lundberg and hi.s collaborators in studies on the effects of L-DOPA on spinal cord reflexes (82). Thè actual mechanisms by which the groups of interneurones produce phases of flexor and extensor activity have not yet been defined, although Grillner (62) and Pearson (I 15) have suggested some possible models.