Which brain areas are responsible for which aspects of grasping?
Journal of vision
URL with Digital Object Identifier
Most neuroimaging studies of both grasping and object recognition have focused on simple objects made from homogenous materials. However, in behavioral experiments with complex objects, we have shown that participants can use visual object shape and material distribution to select optimal grasps based on a combination of factors: natural grasp axis, grasp aperture, the object’s overall weight, and mass distribution. Given that visual perception of object shape and material distribution are putatively a ventral-stream function; whereas, grasping is putatively a dorsal-stream function, we used functional magnetic resonance imaging (fMRI) to characterize the role of brain regions in both streams during grasping of multi-material objects. We recorded brain activation while participants grasped and lifted objects made of wooden and brass cubes at preselected grasp points. To tease apart the different components of grasp selection, grasps were optimized for either torque, grasp aperture, grasp axis, or a combination of these. For example, some grasps were optimal with respect to minimizing torque, but suboptimal with respect to the aperture. Within visual and visuomotor regions of interest, we examined activation levels and patterns (with representational similarity analysis) to infer neural coding of grasp attributes. When participants grasped objects in configurations with high torque – that is when their grips had to counteract object rotation due to gravity – versus low torque, activation was observed in the grasp-selective anterior intraparietal sulcus, aIPS (in the lateral dorsal stream), the reach-selective superior parieto-occipital sulcus, SPOC (in the medial dorsal stream), and the object-selective lateral occipital cortex, LOC (in the ventral stream). These results suggest that when materials and their distribution are relevant for grasping, both visual streams are recruited.