VARIOUS STRATEGIES OF FORELIMB MOVEMENT DURING CONTACT PLACING REACTIONS ELICITED BY TACTILE STIMULATION OF THE DIFFERENT ASPECTS OF A CATSPAW

Forelimb trajectory and the activity of eight muscles operating at the elbow, wrist and digit joints were analyzed during contact placing (C P) reactions elicited by tactile stimuli applied to the lateral (L) or medial (M) side of the cat's forepaw to verify whether a common movem ent strategy was used in these reactions. A tactile stimulus applied t o the lateral side of the paw led, most frequently, to a short-latency activation of the elbow flexor muscles and flexor carpi radialis. Sti mulation of the medial side of the paw produced either a short-latency activation of the elbow flexors or both the elbow flexor and extensor muscles. At the distal joints it most frequently activated extensor c arpi ulnaris and flexor carpi radialis muscles. Different patterns of activation of the muscles during LCP and MCP reactions led to a divers e involvement of elbow flexion and extension movements at the beginnin g of the reactions. LCP was usually initiated by the elbow flexion mov ement whereas during MCP reactions the elbow flexion often appeared wi th a delay due to a brief co-contraction of the elbow flexor and exten sor muscles which temporarily locked the elbow joint. The latter react ion was initiated by a backward/upward movement at the proximal joints accompanied by an ulnar deviation and a palmar flexion of the paw. Th e medio-lateral components of the movement were also clearly different in LCP and MCP reactions, both at the proximal and distal joints. The results indicate that various strategies of movement are used in CP r eactions depending on the site of tactile stimulation.