Cesqui Benedetta, Macrì Giovanna, Dario Paolo, Micera Silvestro
Lucca Institute for Advanced Studies, IMT, Italy.
J Neuroeng Rehabil. 2008 Nov 19;5:31. doi: 10.1186/1743-0003-5-31.
In the past, several research groups have shown that when a velocity dependent force field is applied during upper limb movements subjects are able to deal with this external perturbation after some training. This adaptation is achieved by creating a new internal model which is included in the normal unperturbed motor commands to achieve good performance. The efficiency of this motor control mechanism can be compromised by pathological disorders or by muscular-skeletal modifications such as the ones due to the natural aging process. In this respect, the present study aimed at identifying the age-related modifications of upper limb motor control strategies during adaptation and de-adaptation processes in velocity dependent force fields.
Eight young and eight elderly healthy subjects were included in the experiment. Subjects were instructed to perform pointing movements in the horizontal plane both in a null field and in a velocity dependent force field. The evolution of smoothness and hand path were used to characterize the performance of the subjects. Furthermore, the ability of modulating the interactive torque has been used as a paradigm to explain the observed discoordinated patterns during the adaptation process.
The evolution of the kinematics during the experiments highlights important behavioural differences between the two groups during the adaptation and de-adaptation processes. In young subjects the improvement of movement smoothness was in accordance with the expected learning trend related to the consolidation of the internal model. On the contrary, elders did not show a coherent learning process. The kinetic analysis pointed out the presence of different strategies for the compensation of the external perturbation: older people required an increased involvement of the shoulder with a different modulation of joint torque components during the evolution of the experiments.
The results obtained with the present study seem to confirm the presence of different adaptation mechanisms in young and senior subjects. The strategy adopted by young subjects was to first minimize hand path errors with a secondary process that is consistent with the optimization of the effort. Elderly subjects instead, seemed to shift the importance of the two processes involved in the control loop slowing the mechanism optimizing kinematic performance and enabling more the dynamic adaptation mechanism.
过去，多个研究小组表明，在上肢运动期间施加速度依赖力场时，经过一些训练后受试者能够应对这种外部扰动。这种适应是通过创建一个新的内部模型来实现的，该模型包含在正常的未受扰动的运动指令中以实现良好的表现。这种运动控制机制的效率可能会受到病理障碍或肌肉骨骼改变（如自然衰老过程导致的改变）的影响。在这方面，本研究旨在确定在速度依赖力场的适应和去适应过程中上肢运动控制策略与年龄相关的改变。
八名年轻和八名老年健康受试者参与了实验。受试者被指示在零场和速度依赖力场中在水平面上进行指向运动。平滑度和手部路径的演变被用来表征受试者的表现。此外，调节交互扭矩的能力已被用作一种范式来解释适应过程中观察到的不协调模式。
实验过程中的运动学演变突出了两组在适应和去适应过程中的重要行为差异。在年轻受试者中，运动平滑度的改善与与内部模型巩固相关的预期学习趋势一致。相反，老年人没有表现出连贯的学习过程。动力学分析指出了补偿外部扰动的不同策略的存在：在实验过程中，老年人需要增加肩部的参与，并对关节扭矩分量进行不同的调节。
本研究获得的结果似乎证实了年轻和老年受试者中存在不同的适应机制。年轻受试者采用的策略是首先最小化手部路径误差，其次是与努力优化一致 的过程。相反，老年受试者似乎改变了控制回路中两个过程的重要性，减缓了优化运动学表现的机制，并更多地启用了动态适应机制。
