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Robert L. Whitwell, Philippe A. Chouinard, Melvyn A. Goodale; Visual feedback modulates BOLD activity in the posterior parietal cortex more so for visually-guided grasping than for visually-guided reaching. Journal of Vision 2010;10(7):1085. doi: 10.1167/10.7.1085.
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© ARVO (1962-2015); The Authors (2016-present)
When we reach out to grasp an object, the visuomotor system uses vision to direct our hand to the object's location and scale our grip aperture to the object's size. Several lines of evidence from human and non-human primate studies have implicated a network of structures in the posterior parietal cortex (PPC) in the programming and updating of visually guided grasping. The present study was designed to examine whether the availability of visual feedback during movement execution would modulate patterns of brain activation in the PPC for visually-guided reach-to-grasp movements. Participants were asked to either reach out and touch or reach out and grasp novel 3-D objects with or without visual feedback throughout the movement. A voxel-wise analysis was carried out using a 2 (task) x 2 (feedback) ANOVA. Not surprisingly, the availability of visual feedback was found to increase activation in many visual areas in both the dorsal and ventral streams. In addition, grasping (as compared to reaching) invoked activity in motor areas (premotor and primary motor cortex), early visual areas (striate and extra-striate cortex), and areas in both the dorsal [e.g., anterior intraparietal sulcus (aIPS) and superior parietal lobule (SPL)] and ventral (lateral occipital complex, fusiform gyrus, and inferior temporal cortex) streams of visual processing. Importantly, however, task by feedback interactions were observed in several dorsal stream regions. In the right SPL, the left aIPS, and the precuneus in both hemispheres, visual feedback increased the level of activation associated with reach-to-grasp movements relative to those made without visual feedback, a difference that was not apparent in the levels of activation associated with reach-to-touch movements. Taken together, these results add to a growing body of evidence that implicates the PPC in the programming, online monitoring, and updating of visually guided grasping.
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