TEMPORAL STRUCTURE OF BIMANUAL GOAL-DIRECTED MOVEMENT SEQUENCE IN MONKEYS

The aim of the present investigation was to assess a bimanual goal-ori ented movement sequence with particular emphasis on its temporal struc ture. The three monkeys (Macaca fascicularis) used in this study chose the left arm as the leading and more postural arm to reach out and pu ll back a spring-loaded drawer containing a food morsel. The right arm followed the left and picked up the food with a precision grip. Video recordings, trajectory recordings of the two index fingers, drawer di splacement and the measurements of discrete events of the left and rig ht hand revealed a considerable trial-by-trial variability in the temp oral and spatial domain. The variability of latencies progressively in creased from the initiation of the bimanual sequence to the left-hand and right-hand events defining goal achievement. The main result was t hat, in spite of this variability in each of the two limbs, there was an invariant left - right goal-related synchronization. The timing of the goal-related event pairs covaried and showed high correlation coef ficients. Covariation of the two hands resulting in an invariant synch ronization was particularly striking when monkeys performed the task w ithout vision, and timing of right and left movement components was de layed with further increase in variability. The results indicate that, in the present bimanual skill, kinaesthetic signals may be sufficient to coordinate the two limbs in a goal-oriented unitary action in acco rd with a memorized plan.