Integration of multisensory information for skilled grasp

我一直对人类的手很着迷，这是我们与环境互动的主要器官。如果我们因疾病或创伤而失去使用双手的能力，我们与环境的身体互动就会受到严重威胁。在我们的日常生活中，我们用手抓住和操纵数以百计的物体和工具，显然毫不费力的优雅。例如，如果我看到桌子上有一支笔，我可以伸出手来，抓住它并使用它，看到笔不仅告诉我可以到达多远，而且还唤起了关于物体可能有多重以及其质量分布的记忆。这意味着，当我的手已经达到笔，它是在正确的方向和位置拿起它，并准备写。当我触摸笔时，来自手的感觉告诉我我对它的重量或大小的估计是否正确，如果不正确，我使用新获得的信息来更新我的动作。视觉提供了关于大小和方向的准确信息;相比之下，手可以有效地“看到”角落，并可以感觉到纹理，以便我们知道表面有多滑。因此，为了熟练地抓握，大脑需要从多个感官来源提取信息，主要是视觉和触觉。以前，我研究了大脑如何将关于物体的视觉信息传递到运动系统。然而，这只是图片的一半，我相信现在至关重要的是要了解大脑如何整合其他感官形式来规划我们与环境的互动。只有当我们接触到一个物体时，来自触摸的信息才变得可用。因此，为了规划抓握动作，大脑需要使用存储的物体触觉特性记忆。在与物体接触后，大脑可以使用新鲜的触觉线索来巩固这种记忆，并在需要时更新抓握。这就提出了一种可能性，即可能存在两种不同的机制来处理相关的视觉和触觉信息。视觉信息将首先与触觉记忆相结合。然后，在物体接触后，视觉将与当前的触觉线索一起处理。这个项目是关于视觉和触觉如何以及在大脑中的何处结合起来控制抓握。当我们接触到物体时，大脑是如何从主要的视觉控制切换到视觉/触觉控制的？这些问题之所以重要，有若干原因。改善来自器械和工具的触觉反馈可以提高灵活性;这对于外科医生和技术人员等专业人员来说非常重要。更好地了解视觉和触觉是如何整合的，也将使我们能够开发出能够复制人类抓握的机器，并直接使瘫痪患者受益。最后，一些神经系统疾病（如中风和周围神经病）影响手部感觉运动控制，削弱了使用感觉输入控制抓握的能力：了解这种控制如何整合这些输入可能有助于我们设计更好的策略来改善他们的生活质量。我计划在虚拟现实环境中研究抓握运动，在这种环境中，我可以控制物体的视觉，而不需要触摸。我将测试在抓握动作的不同阶段，每个因素是如何影响其他因素的。这些实验将揭示改变视觉和触觉之间的平衡如何影响抓握行为。为了了解这是如何反映在大脑中的，我将使用经颅磁刺激，一种直接通过完整头皮无痛刺激大脑的方法，结合大脑扫描方法，揭示大脑的活动模式。这将有助于研究参与处理视觉和触觉的大脑皮层区域如何相互作用并将信息传递到运动皮层。这些方法应该详细阐明视觉和触觉的感觉运动整合所涉及的大脑机制。

I have always been fascinated by the human hand, the principal organ through which we interact with our environment. If we lose the ability to use our hands due to illness or trauma, our physical interactions with the environment are critically jeopardised. In our daily life, we use our hands to grasp and manipulate hundreds of objects and tools with an apparently effortless grace. For example, if I see a pen on my desk I can reach out, grasp it and use it. The sight of the pen tells me not only how far to reach but it also evokes memories of how heavy the object is likely to be and where its mass is distributed. This means that by the time my hand has reached the pen, it is in the correct orientation and position to pick it up and prepare to write. As soon as I touch the pen, sensations from the hand tell me whether my estimates of its heaviness or size were correct, and if not, I use the newly acquired information to update my movement. Vision provides accurate information about size and orientation; in contrast, the hand can effectively 'see' around corners and can feel textures so that we know how slippery the surface is. Therefore to permit skilled grasp, the brain needs to extract information from multiple sensory sources, and principally, vision and touch.Previously, I studied how the brain transfers visual information about an object to the motor system. However, this is only half of the picture and I believe it is now crucial to understand how the brain integrates other sensory modalities in planning our interaction with the environment. Information from touch only becomes available once we contact an object. Therefore, to plan a grasping action, the brain needs to use stored memories of an object's tactile properties. After contact with the object is made, the brain can use fresh tactile cues to consolidate this memory and update the grasp, if required. This raises the possibility that there might be two different mechanisms by which relevant visual and tactile information are processed. Visual information would first be integrated with tactile memory. Then, after object contact, vision would be processed together with current tactile cues. This project is about how and where in the brain vision and touch are combined to control grasp. How does the brain switch from dominant visual control during reach to combined vision/touch control as soon as we contact the object? These questions are important for a number of reasons. Improving tactile feedback from instruments and tools can improve dexterity; this can be important for professionals such as surgeons and technicians. A better knowledge of how vision and touch are integrated will also allow us to develop machines that can replicate human grasp and directly benefit paralysed patients. Finally, some neurological diseases (such as stroke and peripheral neuropathies) affect the hand sensorimotor control, impairing the ability to use sensory inputs to control grasp: understanding how such control integrates these inputs may help us to devise better strategies to improve their quality of life.I plan to study grasping movements in a virtual reality environment in which I can control vision of an object separately from touch. I will test how each factor influences the other during different phases of a grasping action. These experiments will reveal how changing the balance between vision and touch affects grasping behaviour. To understand how this is reflected in the brain, I will use transcranial magnetic stimulation, a method of painlessly stimulating the brain directly through the intact scalp in conjunction with brain scanning methods that reveal patterns of activity in the brain. This will allow investigating how areas of the cerebral cortex involved in processing vision and touch interact and transfer information to the motor cortex. These approaches should illuminate in detail the brain mechanisms involved in the sensorimotor integration of vision and touch.