Integration of multisensory information for skilled grasp

点击翻译按钮获取中文摘要

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.