[Motor control of gait]

Only the neurophysiological aspects of this complex problem are reviewed, excluding biomechanical data. Animal models (lamprey, cat) are chosen in view of their recent experimental and theoretical contributions to the field. Three levels of neural organization are considered: spinal level of central pattern generator (CPG): its existence and function are described with emphasis on its neurochemical constituents; moreover, sensory feedback from proprioceptive and cutaneous inputs--acting in specific phase with the locomotor rythm--is discussed; supraspinal modulations, either tonic or phasic: several brainstem loci (relaying through the median reticular formation) are key-structures in the tonic drive of the spinal locomotor network whereas vestibular nuclei and red nucleus are respectively involved in phasic modulation of extensor and flexor activities; moreover, the cerebellum receiving efference copy from the spinal network--plays a major role in the control of these subcortical systems; "superior" adaptations for skilled locomotion: a possible visuo-motor coordination by the motor cortex and cortico-spinal tract is finally proposed, based on recording and microstimulation experiments in the cat.