Few studies have directly compared the visuo-motor transformation of grasp pre-shaping or transport-grasp coordination of reach-to-grasp movements between the two hands. Our objective was to determine if there are manual asymmetries in right-handed adults as a foundation to investigate hemispheric specialization in individuals post-stroke. Twelve non-disabled right-handed adults performed rapid reach-to-grasp movements to cylinders of three sizes as vision of the arm and hand was partially occluded. We reasoned that the hand system (left or right) that is superior in anticipatory planning of aperture scaling and movement preparation would be more likely to exhibit early grasp pre-shaping under this experimental manipulation. Movement time, hand path, transport velocity, and aperture were derived from 3D electromagnetic sensor data. The visuo-motor transformation of object sizes into an action of aperture pre-shaping was quantified using the correlations between initial aperture velocity and object diameter, and peak aperture and object diameter. Coordination between hand transport and aperture grasping was quantified using the cross-correlation between transport velocity and aperture size. Peak aperture and object diameter were strongly correlated for both hands. However, early aperture velocity and object diameter were correlated only for left-hand movements. Cross-correlation analyses revealed a strong association between transport velocity and aperture only for right-hand movements. Together, these results suggest earlier anticipatory control for the left hand in the visuo-motor transformation of grasp pre-shaping and a stronger transport-grasp linkage for the right hand. Further, initial aperture velocity was a more sensitive measure of these manual asymmetries than peak aperture. Our findings compliment the specialization previously observed for pointing movements of the dominant and non-dominant hemispheric/limb system and the coordinated control of complex movements and visuo-spatial components, respectively.

Background. Intensive task-oriented training such as constraint-induced movement therapy (CIMT) is thought to engage motor learning and decision-making processes, including anticipatory action planning. Objective. To identify the effects of CIMT on anticipatory hand posture selection and movement time for task-specific reach-to-grasp performance. Methods. Subacute and chronic poststroke participants were recruited into CIMT (n = 10) or non-CIMT (n = 10) groups. Arm and hand functions were assessed before and after 2 weeks with the Wolf Motor Function Test (WMFT), Motor Activity Log (MAL), and a unique skilled reach-to-grasp task designed to test anticipatory hand posture selection. The reach-to-grasp tasks included power and precision grasping in 2 conditions achieved optimally with either a pronated (low difficulty) or supinated (high difficulty) hand posture. Outcome measures included success rate, frequency of optimal strategy selection, and movement time. Results. Between-group comparisons revealed a significant treatment effect for WMFT and MAL scores. The CIMT group showed larger gains in success rate, optimal posture selection (precision grasp only), and faster movement times for the supinated conditions. Conclusion. Together, a faster movement time and greater frequency of optimal hand posture selection in the more difficult task condition highlights a set of novel findings. These results provide evidence for training-induced improvements in upper-extremity function that support neurobehavioral recovery more than compensation. Although these findings are preliminary in view of the small sample size, the authors suggest that they may be useful to design and power larger-scale studies to further the understanding of the fundamental mechanisms induced by task-oriented training interventions in neurorehabilitation.