Alberts J L, Tresilian J R, Stelmach G E
Motor Control Laboratory, Arizona State University, Tempe 85283-0404, USA.
Brain. 1998 Apr;121 ( Pt 4):725-42. doi: 10.1093/brain/121.4.725.
Parkinson's disease patients and control subjects performed a simultaneous bilateral reach-to-grasp task to two different sized objects and then pulled the two objects apart. The first phase of the task (reaching-to-grasp) allowed us to examine the issue that impairments in simultaneous movements for Parkinson's disease patients are seen in some tasks but not in others. It is suggested that the reason for this selective impairment is that Parkinson's disease compromises the ability to control multiple task-level degrees of freedom independently and concurrently (task-level degrees of freedom are defined as the number of independent parameters that require specification to perform the task). The first phase was used to test the hypothesis that Parkinson's disease results in a reduction of degrees of freedom that are independently controlled. It was predicted that Parkinson's disease patients would produce similar (homologous) movements of the two limbs (a symmetrical pattern) if the target objects have different accuracy requirements when they reach bilaterally to the two objects. For bilateral reaches for two different-size objects, only the control group showed reliably different patterns in the two limbs (asymmetrical pattern), while the Parkinson's disease group displayed a symmetrical pattern. These results provide support for the hypothesis that Parkinson's disease patients have a reduced capability to control multiple task-level degrees of freedom. The second phase of the task, which involved a transition from position control (reaching-to-grasp) to force control (stabilizing and pulling) was used to examine the ability of Parkinson's disease patients to make transitions between movement tasks and force control. In contrast to control subjects, Parkinson's disease patients produced staircase patterns for grip and load forces. Furthermore, a breakdown in the parallel co-ordination between grip and load force was observed for Parkinson's disease patients. These data suggest that Parkinson's disease disrupts the normal feedforward operations responsible for the co-ordination between grip and load forces.
帕金森病患者和对照组受试者执行了一项同时对两个不同大小物体进行双侧伸手抓握的任务，然后将这两个物体拉开。任务的第一阶段（伸手抓握）使我们能够研究这样一个问题：帕金森病患者在某些任务中会出现同时运动受损的情况，但在其他任务中却不会。有人认为，这种选择性损伤的原因是帕金森病损害了独立且同时控制多个任务级自由度的能力（任务级自由度被定义为执行任务所需指定的独立参数的数量）。第一阶段用于检验帕金森病会导致独立控制的自由度减少这一假设。据预测，如果目标物体在双侧伸手抓握时具有不同的精度要求，帕金森病患者的双侧肢体将产生相似（同源）的运动（对称模式）。对于双侧伸手抓握两个不同大小的物体，只有对照组在双侧肢体上表现出可靠的不同模式（不对称模式），而帕金森病组则表现出对称模式。这些结果为帕金森病患者控制多个任务级自由度的能力降低这一假设提供了支持。任务的第二阶段，即从位置控制（伸手抓握）过渡到力控制（稳定和拉动），用于检验帕金森病患者在运动任务和力控制之间进行转换的能力。与对照组受试者不同，帕金森病患者在握力和负载力方面产生了阶梯状模式。此外，还观察到帕金森病患者在握力和负载力之间的平行协调出现了中断。这些数据表明，帕金森病扰乱了负责握力和负载力协调的正常前馈操作。
