fMRI adaptation for real actions The Human Dorsal Stream Adapts to Real Actions and 3D Shape Processing: A Functional Magnetic Resonance Imaging Study

We tested whether or not the control of real actions in an ever-changing environment would show any dependence on prior actions elicited by instructional cues a few seconds before. To this end, adaptation of the functional magnetic resonance imaging signal was measured while human participants sequentially grasped three-dimensional objects in an event-related design, using grasps oriented along the same or a different axis of either the same or a different object shape. We found that the bilateral anterior intraparietal sulcus (aIPS), an area previously linked to the control of visually-guided grasping, along with other areas of the intraparietal sulcus, the left supramarginal gyrus (SMG) and the right mid superior parietal lobe (mid-SPL) showed clear adaptation following both repeated grasps and repeated objects. In contrast, the left ventral premotor cortex (PMv), and the bilateral dorsal premotor cortex (PMd), the two premotor areas often linked to response selection, action planning and execution, showed only grasp-selective adaptation. These results suggest that, even in real action guidance, parieto-frontal areas demonstrate differential involvement in visuomotor processing dependent on whether the action or the object has been previously experienced. signal have been recently used not only to investigate the neural bases of implicit and explicit perceptual and semantic memory (Buckner and Koutstaal 1998), but also to test the properties of smaller populations of neurons in object-responsive areas of the human brain. For example, changes in the blood oxygenation level dependent (BOLD) response following the repeated presentation of stimuli have been successfully utilized to probe differences in processing between (1) brain regions (Buckner et al. 1998), (2) various types of stimuli – e.g., familiar vs. unfamiliar (Henson et al. 2000), and (3) processing phases (James et al. 1999). Most importantly, though, the effects of stimulus repetition have been used to study higher-level processing in the visual perceptual areas (Grill-Spector et al. 1999; Grill-Spector and Malach 2001). Because the phenomenon of repetition suppression or fMR adaptation allows inferences about neural populations at a finer scale than the true spatial resolution, it is sometimes said to provide " hyper-resolution. " That is, as argued by Grill-Spector et al. (1999), within the confines of a functional area or even a smaller cluster of voxels, conventional subtraction methods may fail to distinguish between neurons with different selectivities. If, however, these neurons show response change (e.g., suppression of activation) following back to back presentations of the same stimulus, the average activity within …