Coordinating movements using optimal control: A neuro-computational perspective

关于人类运动控制的大部分研究都考察了人类如何移动身体的单个部位，如手臂或眼睛。然而，我们的日常行动是由身体多个部位同时运动组成的。例如，我们用双手系鞋带。即使是举起一只手臂的简单动作，也会伴随着腿部肌肉的变化来稳定站姿。对于许多患有神经性中风或疾病的患者来说，这些复杂的运动技能往往会带来问题，即使在孤立肢体的简单运动恢复后也是如此。然而，与单一肢体运动相比，我们对神经系统如何在身体不同部位的运动之间实现协调知之甚少。通过指示人类志愿者同时做出两个不同的动作的实验，我们对大脑如何协调复杂的动作有了一些见解。这些实验已经确定了我们独立移动两条肢体的能力的根本局限性。例如，一边揉肚子，一边拍头是相当困难的。然而，进一步的实验表明，这些限制通常并不是硬连接到电机系统中的。相反，它们在很大程度上取决于这些运动的目标。例如，当我们用两只手操作一个物体时，两只手的运动可以强烈地相互依赖，而当我们伸手去拿两个不同的物体时，它们可以完全独立地控制。为了了解大脑如何在这些不同的情况下协调动作，我们将研究人类志愿者如何学习运动任务，在这些任务中，必须协调双手以实现不同的目标。我们将应用工程学和控制论的方法来预测，在给定特定任务目标的情况下，生物体应该如何最佳地协调运动，然后测试这些预测。我们还将研究大脑是如何在协调中实现最佳控制的。例如，控制不同运动部件的大脑区域之间交换的信号是什么？协调是否依赖于“肌肉记忆”/记忆的一套特定肌肉的激活模式？或者，身体的不同部位会通过交换有关它们当前位置和速度的信息来相互“交谈”吗？随着协调技能通过培训变得更加自动化，这些领域的沟通方式将如何变化？功能磁共振成像(FMRI)将被用来测量人类志愿者在执行协调任务时的大脑活动。通过改变任务的目标和要求，我们将能够识别与协调运动有关的神经区域，并指定它们的功能。例如，当我们抓住一个物体时，我们必须协调手臂的运动和握手的手的张开。哪些神经区域参与估计手臂已经向目标移动了多远，这是决定何时开始抓握的重要信号？哪些神经区域接受这些估计并启动手的张开？了解大脑如何协调运动，以及大脑的哪些区域参与了这项任务，对于了解中风或脑部疾病患者面临的协调问题至关重要。这项工作将提供一个理论基础，可以导致新的治疗和康复计划，旨在促进这些人产生复杂运动技能的能力，这些技能超出了产生简单动作的控制要求。

Much of the research on human motor control has examined how humans move a single body part, such as the arm or the eyes. Our everyday actions, however, consist of movements of multiple body parts at the same time. For example, we use both hands to tie our shoes. Even the simple act of raising one arm is accompanied by changes in leg muscles to stabilize stance. For many patients with neurological strokes or disorders, these complex movement skills often cause problems even after simple movements of isolated limbs have recovered. Compared to single limb movements, however, we know very little about how the nervous system achieves coordination between movements of different body parts. We have gained some insights into how the brain coordinates complex movements through experiments in which human volunteers are instructed to produce two different movements at the same time. These experiments have identified fundamental limitations in our ability to move two limbs independently. For example it is quite difficult to rub one's belly and to simultaneously pat one's head. Further experimentation however, has made clear that these limitations are generally not hard-wired into the motor system. Rather they depend crucially on what the goals of the movements are. For example, movements of the two hands can depend strongly upon one another when we manipulate a single object with two hands, and they can be controlled quite independently when we reach out for two separate objects. To understand how the brain coordinates movements in these different situations, we will study how human volunteers learn motor tasks in which the hands must be coordinated to achieve different goals. We will apply approaches from engineering and control theory to predict how, given a specific task goal, an organism should optimally coordinate movements, and will then test these predictions. We will also investigate how specifically the brain achieves optimal control in coordination. For example, what signals are exchanged between regions of the brain that control different movement components? Does coordination depend on 'muscle memory' / a memorized set of activation patterns in particular muscles? Or do different body parts 'talk' to each other by exchanging information about their current position and velocity? How do the ways in which these areas communicate change as coordination skills become more automatic through training? Functional magnetic resonance imaging (fMRI) will be used to measure brain activity in human volunteers while they perform coordination tasks. By changing the goals and requirements of the task, we will be able to identify neural areas that are involved in coordinating movements and specify their function. For example, when we grasp an object we have to coordinate the arm movement and the opening of the hand for grasping. Which neural areas are involved in estimating how far the arm has moved already towards the target, an important signal for deciding when to start the grasp? Which neural areas take these estimates and initiate the opening of the hand? Understanding how the brain coordinates movements and which areas of the brain are involved in this task is essential for understanding the coordination problems faced by patients affected by strokes or brain disorders. This work will provide a theoretical foundation that can lead to new treatments and rehabilitation programs designed to facilitate the ability of these individuals to produce complex motor skills, those that go beyond the control requirements for producing simple movements.