Movement and muscle activity during contact placing of the forelimb and their relations to other postural reactions in the cat

Abstract

Forelimb trajectory and the activity of eight muscles operating at the elbow, wrist and digit joints were compared during the contact placing reaction, during the swing phase of locomotion and during reactions induced by swing perturbations, to verify the hypothesis that common neural mechanisms are involved in these reactions. Both the patterns of muscle activation and forelimb kinetics during the placing reaction greatly differed from those during the swing phase of locomotion. Both similarities and differences have been found between the placing reaction and the reaction to swing perturbations. Similar latencies, patterns of muscle activation and trajectories have been found for elbow movements while considerable differences were seen in the movements of distal joints. Both reactions started with a backward and upward movement at the proximal joints which was accompanied by a locking at the elbow. At the distal joints, tactile stimuli evoked first a wrist ventroflexion during the placing reaction, whereas they induced wrist dorsiflexion to swing perturbations. A further difference between these two reactions appeared at the beginning of the extension which was highly passive during the reaction to swing perturbation and active during contact placing. These results suggest that some common, most likely spinal, reflexes are involved at the beginning of the two reactions while their extension phases are controlled in a different way.