Department of Neurology, University of Duisburg-Essen, Hufelandstrasse 55, 45147 Essen, Germany.
J Neurophysiol. 2010 Feb;103(2):698-708. doi: 10.1152/jn.00337.2009. Epub 2009 Dec 2.
Various studies showed a clear impairment of cerebellar patients to modulate grip force in anticipation of the loads resulting from movements with a grasped object. This failure corroborated the theory of internal feedforward models in the cerebellum. Cerebellar damage also impairs the coordination of multiple-joint movements and this has been related to deficient prediction and compensation of movement-induced torques. To study the effects of disturbed torque control on feedforward grip-force control, two self-generated load conditions with different demands on torque control-one with movement-induced and the other with isometrically generated load changes-were directly compared in patients with cerebellar degeneration. Furthermore the cerebellum is thought to be more involved in grip-force adjustment to self-generated loads than to externally generated loads. Consequently, an additional condition with externally generated loads was introduced to further test this hypothesis. Analysis of 23 patients with degenerative cerebellar damage revealed clear impairments in predictive feedforward mechanisms in the control of both self-generated load types. Besides feedforward control, the cerebellar damage also affected more reactive responses when the externally generated load destabilized the grip, although this impairment may vary with the type of load as suggested by control experiments. The present findings provide further support that the cerebellum plays a major role in predictive control mechanisms. However, this impact of the cerebellum does not strongly depend on the nature of the load and the specific internal forward model. Contributions to reactive (grip force) control are not negligible, but seem to be dependent on the physical characteristics of an externally generated load.
多项研究表明，小脑患者在预期因抓握物体而产生的运动所导致的负荷时，明显无法调节握力。这一失败证实了小脑内前馈模型的理论。小脑损伤还会损害多关节运动的协调性，这与运动引起的转矩的预测和补偿不足有关。为了研究扭矩控制紊乱对前馈握力控制的影响，在小脑变性患者中，直接比较了两种具有不同扭矩控制要求的自产生负载条件——一种是运动引起的，另一种是等长产生的负载变化。此外，人们认为小脑在自我产生的负荷下调整握力的能力比外部产生的负荷更强。因此，引入了另一种外部产生的负荷条件来进一步检验这一假设。对 23 名小脑退行性病变患者的分析显示，在控制这两种自产生的负荷类型时，预测性前馈机制明显受损。除了前馈控制外，当外部产生的负荷使抓握不稳定时，小脑损伤还会影响更具反应性的反应，尽管根据控制实验的结果，这种损伤可能因负荷类型而异。本研究结果进一步支持小脑在预测性控制机制中发挥主要作用。然而，小脑的这种影响并不强烈依赖于负荷的性质和特定的内部前向模型。对（握力）反应性控制的影响不可忽视，但似乎取决于外部产生的负荷的物理特性。
