Figure 1.

Design of three types of experiments. A, E, I, In all experiments, the decerebrate cat was fixed in a rigid frame (points of fixation are indicated by crosses). Walking of the hindlimbs was evoked by stimulation of the mesencephalic locomotor region (MLR-stim) or the spinal cord (SC-stim). A–D, Type 1 experiments. The hindlimbs were positioned on the moving belt of the treadmill, the pelvis was not fixed, and balance in the hindquarters was maintained due to the postural neural mechanisms of the cat. Postural reactions were evoked by the lateral push of the pelvis (Test 1, B) or the lateral treadmill tilt α (Test 2, C and D). E–H, Type 2 experiments. The hindlimbs were positioned on the moving belt of the treadmill, the pelvis was fixed by the pelvis restraint (PR), and no balance control was required. Reactions of individual limbs to destabilizing factors, i.e., to the lateral translation and the lateral pull (Tests 3,4; F), as well as to the lateral tilt (Test 5; G, H) were recorded. I–L, Type 3 experiments. The pelvis was supported by the pelvis restraint that could be moved horizontally to the right and to the left (J), or it was suspended on a long string (I, K, L). The treadmill was removed. A lateral translation of the pelvis was performed by moving PR (Test 6; J) or by applying a constant lateral force, (Test 7; K, L) during air stepping. The anterior–posterior position of each limb was recorded by a sensor; only one sensor (Limb-R) is shown in A, E, I. The contact force under each limb was measured by a force plate (FP). The lateral displacement of the pelvis (S) relative to the sagittal plane (SagPl; C, D, dotted line) was recorded by means of a mechanical sensor. The lateral displacement of the limb (Y) in Tests 3, 4 (F) was recorded by another sensor. The number of animals used in each of three types of experiments, as well as the number of animals subjected to each of seven tests is indicated in parentheses.