Bimanual coordination in monkeys

Abstract

In respect to their agility and muscular coordination, monkeys in which the corpus callosum has been sectioned are hardly distinguishable from normal animals. Nevertheless, certain movement patterns involving the use of both hands might be expected to depend on direct connections between the hemispheres since the main cortical motor centers for each hand lie in opposite hemispheres. In these experiments a behavioral test was used to measure the proficiency in aim and timing of hand movements where the sensory information for direction, distance, and timing of the target came from proprioceptive and kinesthetic cues originating in the other arm. Testing of monkeys with various midline brain lesions showed that section of either the corpus callosum or tectal cross-connections alone produced only a transient loss of skill in the task. If forebrain and midbrain commissures were both severed, however, a long-lasting deficit became apparent when the task was attempted without vision. With visual guidance of hand movement, performance remained essentially normal. With continued postoperative practice over several months the accuracy of spatial coordination of hand movements slowly improved until even when working blind, performance scores were once again normal and further were unaffected by an almost complete midline division of the cerebellum.