Left–Right Interaction during Anticipatory Motor Adjustment

Abstract

The interaction of anticipatory and reflexive changes in the grip force of the right hand was tested for the effect on the grip force developed by the thumb and index finger of the left hand. The test task for the right hand was the same in all test variants, to hold a cup where a weight fell (with the thumb and index finger). Three different tasks were chosen for the left hand. In the first task, the left fingers touched a sensor with a negligible grip force. In the second task, the subject had to hold a force sensor loaded with a 200-g load. In the third task, the subject was instructed to slowly increase the grip force by fingers of both hands. In response to the impact of the falling weight, an involuntary increase was observed in the grip force of the right-hand fingers, depending on the available visual information of the falling weight and being independent of the motor task performed by left hand. When the subject’s eyes were closed, the grip force increased in all tasks as a response to the impact of the weight fall. When the subject’s eyes were open, an automatic increase in the right-hand grip force occurred 200–300 ms before the impact. The left-hand grip force changed in different ways. In the first and second tasks, the grip force of the left hand did not change despite the changes in the grip force of the right hand in response to the impact of the falling weight. In case of a coordinated slow increase in the grip forces of both hands, an increase in the grip force was observed in the unaffected left hand before the impact and during the response to the impact, like in the right hand. Thus, a common motor task for both hands led to similar changes in grip force, which were recorded in both right and left hands not only during the response to an external stimulus, but also during anticipation. Movement planning was assumed to involve the organization of left–right interaction at the supraspinal level, probably, at the level of motor cortex interactions between the left and right hemispheres.