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Abstract:
There is general agreement about the posterior parietal cortex, in particular the anterior part of the intraparietal sulcus (aIPS), being engaged in visually guided grasping. The contribution of these areas to memory-guided grasping, however, is still controversial. Electrophysiological studies in monkeys suggest a role of the aIPS in both visually guided and memory-guided grasping. However, some results from patients suggest a dissociation such that the aIPS is involved in immediate grasping while the inferior temporal cortex is involved in memory-guided grasping. Using functional magnetic resonance imaging, we investigated the neural correlates of immediate and delayed grasping in healthy humans. Participants were asked to grasp three-dimensional objects of different size and orientation with their thumb and index finger of the dominant right hand (precision grip). Vision was controlled by liquid crystal shutter goggles that were opened during object presentation but closed during grasping, thus requiring open-loop grasping. An auditory signal either presented immediately after object presentation (immediate grasping) or after a variable delay of two to twelve seconds following object presentation (delayed grasping), signalled the start of the grasp movement. We analysed cortical activity during object presentation, maintenance of object information, and immediate and delayed grasping. Object presentation activated areas along the dorsal and ventral visual streams in both hemispheres and the left sensorimotor cortex. Short-term maintenance of action-related object information revealed activation in the right aIPS and adjacent inferior parietal cortex. A similar activation was observed for delayed in contrast to immediate grasping. In line with electrophysiological monkey data, our results indicate that the aIPS does not only contribute to visually-guided grasping but also stores action-related information used for subsequent memory-guided grasping.
