Control of aperture closure initiation during reach-to-grasp movements under manipulations of visual feedback and trunk involvement in Parkinson’s disease

Abstract

The present project was aimed at investigating how two distinct and important difficulties (coordination difficulty and pronounced dependency on visual feedback) in Parkinson's disease (PD) affect each other for the coordination between hand transport toward an object and the initiation of finger closure during reach-to-grasp movement. Subjects with PD and age-matched healthy subjects made reach-to-grasp movements to a dowel under conditions in which the target object and/or the hand were either visible or not visible. The involvement of the trunk in task performance was manipulated by positioning the target object within or beyond the participant's outstretched arm to evaluate the effects of increasing the complexity of intersegmental coordination under different conditions related to the availability of visual feedback in subjects with PD. General kinematic characteristics of the reach-to-grasp movements of the subjects with PD were altered substantially by the removal of target object visibility. Compared with the controls, the subjects with PD considerably lengthened transport time, especially during the aperture closure period, and decreased peak velocity of wrist and trunk movement without target object visibility. Most of these differences were accentuated when the trunk was involved. In contrast, these kinematic parameters did not change depending on the visibility of the hand for both groups. The transport-aperture coordination was assessed in terms of the control law according to which the initiation of aperture closure during the reach occurred when the hand distance-to-target crossed a hand-target distance threshold for grasp initiation that is a function of peak aperture, hand velocity and acceleration, trunk velocity and acceleration, and trunk-target distance at the time of aperture closure initiation. When the hand or the target object was not visible, both groups increased the hand-target distance threshold for grasp initiation compared to its value under full visibility, implying an increase in the hand-target distance-related safety margin for grasping. The increase in the safety margin due to the absence of target object vision or the absence of hand vision was accentuated in the subjects with PD compared to that in the controls. The pronounced increase in the safety margin due to absence of target object vision for the subjects with PD was further accentuated when the trunk was involved compared to when it was not involved. The results imply that individuals with PD have significant limitations regarding neural computations required for efficient utilization of internal representations of target object location and hand motion as well as proprioceptive information about the hand to compensate for the lack of visual information during the performance of complex multisegment movements.

Control of aperture closure initiation during trunk-assisted reach-to-grasp movements

“…Similarly to our previous study of trunk-assisted reach-to-grasp movements (Rand et al 2010a), trunk related movement parameters (trunk-to-target distance, trunk velocity and trunk acceleration) at the time of finger closure initiation were added to our previous control law model which consisted of only the finger and arm related movement parameters (Rand et al 2006a; 2006b; 2007). We hypothesized that the aperture closure is initiated when the hand crosses a hand-to-target distance threshold that is a function of the aperture magnitude, wrist velocity and wrist acceleration, trunk-to-target distance, as well as trunk velocity and trunk acceleration, which were measured at the time of finger closure initiation.…”

“…This approach has been successfully used in our previous study that tested the transport-aperture coordination of reach-to-grasp movement where the trunk never moved (Rand et al 2006a; 2006b; 2007) and where the trunk did move (Rand et al 2010a). A linear approximation of the above model was used to fit the data.…”

“…Furthermore, when a reach-to-grasp movement was performed under a suboptimal condition (i.e. in the absence of vision), trunk involvement during reaching to an object resulted in an increase of grip aperture (Rand et al 2010a). Thus, the degree to which the trunk motion is coordinated with the grasp component depends on the complexity of the prehension task (Marteniuk and Bertram 2001).…”

“…We have shown previously that a highly precise relationship between these movement parameters is established at the initiation of aperture closure during the reach and maintained throughout the aperture closure phase until the target object is grasped (Rand et al 2008; 2010b). In our most recent study, we incorporated trunk dynamics into the aforementioned relationship between the hand-to-target distance and the other movement parameters of the transport and aperture components for grasping initiation (Rand et al 2010a). It is not known, however, how the control law for aperture closure initiation changes when the trunk motion is rigorously manipulated during prehensile movements to targets located within the arm’s reach.…”

Hand Function in Parkinson’s Disease

“…This overreliance on vision may well be due to an impaired ability to extract critical proprioceptive information and integrate it with vision and motor commands [ 6 , 36 ]. Thus, when visual feedback of the object and/or the hand is removed during the reach, PD patients take signifi cantly longer to transport the hand to the object, especially at close range to the target, while producing a greater than normal grip aperture [ 64 ]. Removal of visual feedback of the hand during the reach also exacerbates inappropriate hand preshaping and results in signifi cantly more failed grasps [ 8 ].…”