Interlimb Transfer of Grasp Orientation is Asymmetrical

Short Communication TheScientificWorldJOURNAL (2006) 6, 1805–1809 ISSN 1537-744X; DOI 10.1100/tsw.2006.291 Interlimb Transfer of Grasp Orientation is Asymmetrical V. Frak1,2,*, D. Bourbonnais2, I. Croteau2, and H. Cohen3 1 Département de Kinanthropologie, Université du Québec à Montréal; 2Institut de Réadaptation de Montréal,-CRIR, Université de Montréal; 3Memory and Motor Skills Disorders Research Centre, Clinique Sainte Anne, Québec E-mail: Received July 27, 2006; Revised December 9, 2006; Accepted December 11, 2006; Published December 28, 2006 One the most fundamental aspects of the human motor system is the hemispheric asymmetry seen in behavioral specialization. Hemispheric dominance can be inferred by a contralateral hand preference in grasping. Few studies have considered grasp orientation in the context of manual lateralization and none has looked at grasp orientation with natural prehension. Thirty right-handed adults performed precision grasps of a cylinder using the thumb and index fingers, and the opposition axis (OA) was defined as the line connecting these two contact points on the cylinder. Subjects made ten consecutive grasps with one hand (primary hand movements) followed by ten grasps with the other hand (trailing movements). Differences between primary and trailing grasps revealed that each hemisphere is capable of programming the orientation of the OA and that primary movements with the right hand significantly influenced OA orientation of the trailing left hand. These results extend the hemispheric dominance of the left hemisphere to the final positions of fingers during prehension. KEYWORDS: Prehension. Interlimb transfer. Opposition axis. Hemispheric dominance. Visuomotor transformation INTRODUCTION Reaching and grasping an object is a complex motor task involving the proximal and distal joints. One of the most influential theories of prehensile movements in both primates and humans is that proposed by Jeannerod[1]. In this theory, Jeannerod claims that two distinct processing components are involved in prehension movements: one responsible for the transport of the arm to the object (more dependent on proximal segments of the upper limb) and one for the grip of the object (more dependent on distal segments of the upper limb). It has been presumed that interhemispheric communication is required for the coordination of reaching and grasping[2], supporting the notion that each hemisphere has a predominant involvement during reaching to grasp actions. Previous work supports the idea that grasping is not a purely distal phenomenon, as it also involves the proximal segments of the upper limb. For example, Paulignan et al.[3] studied the action of grasping an object located at different positions in the work field. They found that although the grasp orientation was constant for all positions, the shape of the whole arm changed from one position to another. A study by Stelmach et al.[4] also showed that the *Corresponding author. ©2006 with author. Published by TheScientificWorld, Ltd.; www.thescientificworld.com 1805 Frak et al.: Interlimb Transfer of Grasp Orientation TheScientificWorldJOURNAL (2006) 6, 1805–1809 orientation of the distal part of the movement (finger grip) is not independent from the organization of the proximal part of the movement (reach). In their work, a relatively small change in the orientation of an object, allowing only one possible grasp orientation, resulted in a major reconfiguration of the arm, including wrist pronation and shoulder abduction. Few studies have considered grasp orientation in the context of manual lateralization[5] and none has looked at grasp orientation in free-precision grasp, i.e., with no constraint of finger position on the object. Grasp orientation, defined by the opposition axis (OA), is the final expression of a composite mechanism — reach and grasp — resulting in the controlled precision prehension of an object. In a precision grip formed by the thumb and index fingers, the OA is defined as the line connecting the final position of the fingers on the object. The fingers involved in the grasp represent the effector of the movement and their final position on the object is a main parameter to be controlled for completing a grasp[6]. Location, size (from 3–9 cm), and weight (from 30–300 g) of cylinders do not impact on grasp orientation, which remains stable, with respect to an egocentric reference frame in right-handed individuals[3,7]. In this perspective, the main objective of this study was to examine whether a dominant arm advantage exists in controlling the OA orientation when natural prehension occurs. We used a cylinder where the thumb and index finger could be placed at any position on its surface. METHODS Subjects Thirty, healthy, right-handed adults (14 women and 16 men) volunteered to participate in this investigation. Handedness was determined using the ten-item version of the Edinburgh inventory[8]. Only subjects scoring a laterality quotient of 100 were selected. Subjects ranged in age from 19–70 years (mean = 49). Subjects were recruited and tested following ethical considerations in accordance with the Centre for Interdisciplinary Research in Rehabilitation of Montréal procedures. Before the experiment, subjects were given explanations of the methods used. The purpose of the study was revealed to them once the experiment was over. Procedure The subjects were comfortably seated in front of a table. Subjects were asked to reach, grasp, lift, and return to its original position a smooth 300-g resin cylinder (6 cm in diameter, 10 cm high) placed at the center of the table at a distance of 32 cm from the body plane, using a precision grip formed by the thumb and index fingers only. The OA was defined as the line connecting these two contact points on the cylinder and the OA orientation was calculated with a protractor with respect to the frontal plane. Subjects made ten consecutive grasps with one hand (primary hand movements) followed by ten consecutive grasps with the other hand (trailing hand movements). Fifteen subjects performed the first block of grasps with their right hand and the second block with their left hand. This order was reversed for the other 15 subjects. The initial position of the right hand was 13 cm right of the sagittal axis and 13 cm to the left of the axis for left-hand movements. RESULTS Mean OA orientation from an egocentric frame of reference for primary hand movements was 32° (ranging from 24–40°) for the right and 17° (ranging from 6–23°) for the left. The right-hand OA orientation observed here is in agreement with previous experiments with cylinders of different size, 1806 Frak et al.: Interlimb Transfer of Grasp Orientation TheScientificWorldJOURNAL (2006) 6, 1805–1809 weight, and positions[3,7]. Mean OA orientation for trailing hand movements was 26° (ranging from 14– 38°) for the right and 32° (ranging from 20–42°) for the left (Fig. 1) (...truncated)