Anticipatory corticospinal control of movements in healthy subjects and in patients with neurological motor deficits

当一个人用一只手掌拿着一本很重的书时，如果书突然被其他人举起，手臂会平稳地移动到另一个位置（卸载反射）。如果人自己用另一只手移动书，手臂几乎停留在同一位置（自动卸载）。在预期的自动卸载，大脑可能会修改运动控制信号，使手臂的位置被保留。为了揭示潜在的控制机制，本项目将分析皮质脊髓在两个卸载任务中的影响。 以前的研究表明，阈值手臂的位置，肌肉变得活跃，是一个控制变量的影响皮质脊髓系统。本项目假设，为了在自卸载期间保持手臂位置，受试者将在卸载开始之前和期间开始改变皮质脊髓对阈值手臂位置的影响，并在卸载后保持最终的皮质脊髓影响。为了验证这一假设，将在两个卸载任务之前和之后在初级运动皮层上施加单脉冲经颅磁刺激以触发肌电反应。如果自身卸载前后的诱发肌电反应与卸载反射时的诱发肌电反应不同，则该假设将得到证实，并建立一个预测两种卸载任务的肌电模式和运动学的计算机模型。假设的控制输入是用于卸载反射的恒定阈值位置和用于自卸载的斜坡形阈值位置。模型预测将与实验测量结果进行比较，本项目还将测试中风后受试者是否在自我卸载的预期控制方面存在缺陷。通过比较患者与健康对照组的反应，将确定对运动控制障碍潜在机制的新见解。

When a person holds a heavy book in the palm of one hand and if the book is suddenly lifted off by someone else, the arm moves smoothly to another position (unloading reflex). If the person him/herself moves the book using the other hand, the arm stays almost at the same position (self-unloading). In anticipation of the self-unloading, the brain may modify motor control signals so that the arm position is preserved. To unveil the underlying control mechanisms, this project will analyze the corticospinal influences in the two unloading tasks. Previous studies suggested that the threshold arm position, at which muscles become activated, is a control variable influenced by the corticospinal system. This project hypothesizes that, in order to preserve the arm position during self-unloading, the subject will start changing corticospinal influences on threshold arm position before and during the unloading onset, and will maintain the final corticospinal influences after unloading. To test this hypothesis, single-pulse transcranial magnetic stimulation will be applied on primary motor cortex before and after the two unloading tasks to trigger electromyographic responses. The hypothesis will be confirmed if evoked electromyographic responses before and after self-unloading are different from those during unloading reflex.A computer model which predicts electromyographic patterns and movement kinematics will be developed to simulate the two unloading tasks. The hypothetical control input is a constant threshold position for unloading reflex and a ramp-shaped threshold position for self-unloading. Model prediction will be compared with experimental measurements.This project will also test whether or not post-stroke subjects have deficits in anticipatory control of self-unloading. By comparing responses elicited in the patients to healthy controls, new insights into the mechanisms underlying disordered motor control will be identified.