Effects of error size and error distribution on mechanisms of sensory motor adaptation

由于生长、衰老和疾病，人体运动系统受到肌肉激活及其效应之间关系的自然变化的影响。尽管有这些变化，但由于神经元运动控制的自适应能力允许补偿这些变化，运动性能可以在长时间的生活中保持。在最简单的情况下，运动适应的特征在于运动误差的指数衰减，其时间常数与运动误差及其历史无关。然而，许多以前的研究表明，这种线性模型只近似于真实的适应过程的动态，并且1）运动误差的衰减可以通过具有不同时间常数的指数的叠加来描述，2）误差衰减非线性地依赖于运动误差的大小，以及3）在更近的观察中，时间常数被证明是时变的。理论上的考虑表明，时间常数取决于错误的敏感性和保留。相应地，先前对适应机制的时间依赖性的解释表明，错误敏感性或保留本身（类似于运动命令）是由运动错误的时间序列驱动的动态过程的结果。因此，这些模型不仅考虑了电机指令的自适应，而且考虑了一种元自适应，通过该元自适应，系统能够根据实际情况调整误差敏感性和主自适应过程的保持。由于以往的研究集中在错误敏感性或保留，有一个缺乏的研究调查这两个特点的主要adaptationprocess.The项目的主要目标是实验观察的时间过程中的错误敏感性和保留因子作为错误大小的函数在一个单一的适应块或一系列的适应块。在两个子项目中，这些研究将在1）由眼内目标位移引起的眼跳幅度适应和2）旋转光标反馈的到达适应中进行。常见的问题是错误敏感性和保持因子在不同的主题和不同的条件下是否遵循一定的模式（相同或相反的差异），或者这两个特征的运动适应是相互独立的。受试者之间的差异意味着一组健康对照受试者内的差异，以及小脑患者和健康对照之间的组差异。这项研究的一个特别重点是小脑在上述元适应中的作用。

The human motor system is subject to natural changes of the relations between muscle activation and its effects, due to growth, aging, and disease. Despite these changes, motor performance can be maintained over long periods of life thanks to the adaptive capabilities of neuronal movement control which allows compensation for these changes. In the simplest case, motor adaptation is characterized by an exponential decay of the motor error, the time constant of which is independent of the motor error and its history. However, many previous studies suggest that such a linear model only approximates the dynamics of real adaptation processes and that 1) the decay of the motor error may be described by a superposition of exponentials with different time constants, 2) the error decay depends non-linearly on the size of the motor error, and 3) the time constants prove to be time-variant on closer observation. Theoretical considerations showed that the time constant depends on both error sensitivity and retention. Correspondingly, previous explanations of the time dependence of the adaptation mechanisms suggested that error sensitivity or retention is itself (similar to the motor command) the result of a dynamic process driven by the temporal sequence of motor errors. Thus, these models consider not only the adaptation of the motor command but also a kind of meta-adaptation by which the system is able to adjust error sensitivity and retention of the primary adaptation process according to the actual conditions. Since previous studies focused on either error sensitivity or on retention, there is a lack of studies investigating both of these characteristics of the primary adaptation process in parallel.The main objective of this project is the experimental observation of the time courses of error sensitivity and retention factor as a function of error size during a single adaptation block or a sequence of adaptation blocks. In two subprojects these investigations will be performed 1) in saccade amplitude adaptation induced by intrasaccadic target displacement and 2) in reach adaptation to rotated cursor feedback. The common question is whether differences of error sensitivity and retention factor across subjects and across different conditions follow a certain pattern (either same or opposite differences) or whether these two features of motor adaptation are independent of each other. Differences across subjects mean differences within a group of healthy control subjects, as well as group differences between cerebellar patients and healthy controls. A particular focus of the study is the role of the cerebellum in the mentioned meta-adaptations.