Neural correlates of two imagined egocentric transformations

Two egocentric spatial transformation tasks, hand and perspective rotation, were compared using the same visual stimulus within both block and event-related functional magnetic resonance imaging (fMRI) paradigms. Both involved body-relative judgments but were predicted to vary in the recruitment of the body schema and a motor execution system. The Hand task required the imagined rotation of one's own hand to make a left-right handedness decision. In contrast, the Viewer task required a perspective transformation and updating of the parts of a hand as an object. Previous behavioral and neuroimaging work suggested that hand rotations would rely on dynamic and biomechanical processing of body-part relations recruiting a motor processing system, whereas perspective transformations and the updating of object-self relations would be supported by primarily visual-spatial mechanisms. There was a common neural substrate found for both tasks including the lateral occipital areas, inferior and superior parietal cortex, and the cerebellum. Direct comparisons between the two tasks revealed greater activation in the Hand task in left superior and inferior parietal and premotor cortex and cerebellum, whereas the Viewer task showed greater activation only in the right lingual and fusiform gyri. Degree of rotation also modulated activity in the Hand task in bilateral superior parietal and premotor cortex, but not in the Viewer task. Implications of these regions for the role of dynamic body schema and motor processing in egocentric transformations are discussed.