Control of aperture closure during reach-to-grasp movements in parkinson’s disease

Abstract

This study examined whether the pattern of coordination between arm-reaching toward an object (hand transport) and the initiation of aperture closure for grasping is different between PD patients and healthy individuals, and whether that pattern is affected by the necessity to quickly adjust the reach-to-grasp movement in response to an unexpected shift of target location. Subjects reached for and grasped a vertical dowel, the location of which was indicated by illuminating one of the three dowels placed on a horizontal plane. In control conditions, target location was fixed during the trial. In perturbation conditions, target location was shifted instantaneously by switching the illumination to a different dowel during the reach. The hand distance from the target at which the subject initiated aperture closure (aperture closure distance) was similar for both the control and perturbation conditions within each group of subjects. However, that distance was significantly closer to the target in the PD group than in the control group. The timing of aperture closure initiation varied considerably across the trials in both groups of subjects. In contrast, aperture closure distance was relatively invariant, suggesting that aperture closure initiation was determined by spatial parameters of arm kinematics rather than temporal parameters. The linear regression analysis of aperture closure distance showed that the distance was highly predictable based on the following three parameters: the amplitude of maximum grip aperture, hand velocity, and hand acceleration. This result implies that a control law, the arguments of which include the above parameters, governs the initiation of aperture closure. Further analysis revealed that the control law was very similar between the subject groups under each condition as well as between the control and perturbation conditions for each group. Consequently, the shorter aperture closure distance observed in PD patients apparently is a result of the hypometria of their grip aperture and bradykinesia of hand transport movement, rather than a consequence of a deficit in transport-grasp coordination. It is also concluded that the perturbation of target location does not disrupt the transport-grasp coordination in either healthy individuals or PD patients.

Effect of speed manipulation on the control of aperture closure during reach-to-grasp movements

“…Furthermore, it appears that the same model can accurately describe the control law employed by all participating subjects. These results are fully consistent with data from our previous study in which we found that the control law related to grasp initiation is similar even between healthy controls and Parkinson patients (Rand et al 2006). Thus, the state of arm reach (velocity and acceleration) and state of grasp (aperture amplitude) are likely taken into account by the CNS in order to control the initiation of the aperture closure.…”

“…In our study, we used it to elucidate the relationship between arm movement parameters and a decision to initiate aperture closure. The existence of such a control law has been shown also in our previous study (Rand et al 2006). This study demonstrates that the aperture closure distance significantly increases with faster transport speed across a range of speed conditions.…”

“…This approach has been successfully used in our previous study (Rand et al 2006). The coefficients of a particular model of the control law were identified based on the standard method, namely by minimizing the least square deviation of the model's prediction from the actual, experimentally measured values of the target variable (the aperture closure distance or aperture opening time).…”

The impact of subthalamic deep brain stimulation on bradykinesia of proximal and distal upper limb muscles in Parkinson's disease

“…For reach-to-grasp movements in PD patients a slowing of hand transport and a discoordination between hand transport and grasp formation with a pronounced delay of the onset of the grasp opening has been documented [8][9][10]21]. Interestingly, we found that STN-DBS shortened the time of peak grasp aperture in relation to the time of hand transport and thus normalized the temporal coupling between the reach and grasp components of the reach-to-grasp task in PD.…”

Fine Motor Function Skills in Patients with Parkinson Disease with and without Mild Cognitive Impairment

“…The subtest dexterity measures coordinated and independent finger movements and requires skills for grasping and holding the pins and putting them into an intended target. As mentioned in the introduction, PD patients already have difficulties in movement initiation to the target [11] and in the coordination of fine motor function of the moving hand [12,31,32]. Plotnik et al [33] reported that PD patients and elderly subjects responded substantially slower to a required movement modification than to the initial movement required.…”