GRASPING OBJECTS - THE CORTICAL MECHANISMS OF VISUOMOTOR TRANSFORMATION

Grasping requires coding of the object's intrinsic properties (size an d shape), and the transformation of these properties into a pattern of distal (finger and wrist) movements. Computational models address thi s behavior through the interaction of perceptual and motor schemas. in monkeys, the transformation of an object's intrinsic properties into specific grips takes place in a circuit that is formed by the inferior parietal lobule and the inferior premotor area (area F5). Neurons in both these areas code size, shape and orientation of objects, and spec ific types of grip that ave necessary to grasp them. Grasping movement s are coded more globally in the inferior parietal lobule, whereas the y are move segmented in area F5. In humans, neuropsychological studies of patients with lesions to the parietal lobule confirm that primitiv e shape characteristics of an object for grasping are analyzed in the parietal lobe, and also demonstrate that this 'pragmatic' analysis of objects is separated from the 'semantic' analysis performed in the tem poral lobe.