The postural support of movement in cat and dog.

The postural adjustment which accompanies single limb movement in the standing cat and dog was analyzed. Four trays equipped with strain gauges were used for measuring the vertical forces exerted by each limb before and during movement performance. Three types of movements were analyzed: flexion movements elicited by motor cortex stimulation, placing movements, conditioned movements of either forelimb or hindlimb (lift-off in cat, flexion with maintained final position in dog). In both cats and dogs the postural adjustment during movement consists of a bipedal stance on two diagonally opposite limbs. Large quantitative differences were observed depending on the type of movement. Cortical stimulation elicited an adjustment where changes of forces exerted by the forelimb a hindlimb were nearly equal. During conditioned fore- and hindlimb lift-off in the cat there was a tendency to use only forelimbs for the postural adjustment associated with forelimb movement and hindlimbs for the adjustments associated with hindlimb movement. For placing in the cat and conditioned movement in the dog, the adjustment was intermediate, that is a predominant contribution of forelimb support with forelimb movements but nevertheless an associated contribution from hindlimbs. The general significance of the results with respect to the mechanism of postural adjustment associated with movement is analyzed.