Cortical mechanisms subserving tool-use

当我们使用工具时，它在物理上和感知上都成为手的延伸。因此，在使用工具的过程中，我们的身体形象会根据手头工具的特点而改变。因此，我们可以在精神上操纵我们的身体形象。体感和视觉信息的整合对于创建这样的图像是不可或缺的。这很可能发生在顶叶内皮层，在那里躯体感觉信息的分级处理与空间视觉信息的处理沿着背流沿着进行。在猴的这一皮层区域，我们发现了一组双峰神经元，它们编码身体意象的各个方面，这些方面受到心理操纵：双峰神经元的视觉感受野（V-RFs）包围并锚定在它们的躯体感觉感受野（S-RFs）上，好像编码手在空间中的视觉意象。其他双峰神经元的V-RF编码可达空间的领土。在工具使用过程中，这些V-RF被修改，以包括工具的整个长度或覆盖扩展的可触及空间。当通过视频监视器而不是直接看到手部运动时，这些双峰神经元似乎将视频屏幕中的图像编码为猴子自己身体的投影。我们可以在黑暗中有目的地移动手臂，而不需要视觉反馈，也许是使用大脑产生的手臂图像。当手臂被无形地移动时，V-RE跟随无形的S-RE。这意味着这些双峰神经元通过参考躯体感觉信息来编码手臂姿势的精神维持和更新的视觉图像。

When we use a tool, it becomes an extension of the hand both physically and perceptually. Thus, during tool-use, our body image is altered in accordance with the characteristics of the tool at hand. Thus, we can mentally manipulate our body image. Integration of somatosensory and visual information is indispensable for creating such an image. This most likely takes place in the intraparietal cortex, where the hierarchical processing of somatosensory information adjoin the information on spatial vision processed along the dorsal stream. In this cortical region of monkeys, we found groups of bimodal neurons coding various aspects of the body image which are subject to mental manipulation as follws :Visual receptive fields (V-RFs) of bimodal neurons encompassed, and were anchored to, their somatosensory receptive fields (S-RFs) as if coding visual image of the hand in the space. V-RFs of other bimodal neurons coded the territory of accessible space. During tool-use, those V-RFs were modified so as to include the entire length of the tool or to cover the expanded accessible space. When watching hand movement through a video monitor instead of seeing it directly, these bimodal neurons seemed to code the image in the video screen as a projection of monkey's own body. These modification was observed only in well-trained monkeys intending to use tools.We can move arms purposefully in the dark without visual feedback of the arm movement, perhaps using mentally produced image of the arm. Visual stimuli near the S-RFs activated a group of bimodal neurons even after the hand was hidden invisible ; when the arm was moved invisibly, the V-RE followed invisible S-RE.This would imply that these bimodal neurons code mentally maintained and updated visual images of the arm postures by referring to somatosensory information.