CHARACTERISTICS OF POSTURE ALTERATIONS ASSOCIATED WITH A STEPPING MOVEMENT IN CATS

The relationship between changes in posture and the performance of a f orelimb movement required for a transition between two stance position s was analysed in cats. The task consisted of an operantly conditioned , forelimb stepping movement from one support platform to another loca ted more anterior. The reward was given only after a specific vertical force was applied to the second platform. This ensured that the cat p erformed a clear transition from its initial stance posture to another requiring a different weight distribution. The strategy adopted by an animal during the conditioned movement was studied by analysing the d istribution of the vertical forces as a function of time. Specific qua ntitative functions were used to describe the weight distribution in t he anterior-posterior, right-left and diagonal directions as the task was performed. The temporal parameters characterising this behaviour w ere not significantly different between animals, except for reaction t imes. In contrast, spatial parameters reflected in the distribution of vertical forces generated during the performance of the task were cha racteristic for each animal. As a consequence, a variety of strategies were employed. Nevertheless some general features were found, includi ng the persistence of a diagonal support pattern during the phasic par t of the movement, and ail Initial movement to the side of the forepaw performing the movement. The findings support the view that each anim al exhibits a specific strategy for performing this well-learned task, and that the strategy is consistently employed over consecutive trial s of the movement.