Parietal Cortex Mediates Visuospatial Imagery.

Abstract:
Despite numerous neuroimaging studies there is still no consensus about the neuroanatomical substrate of visual imagery. A possible solution is that different types of imagery are subserved by different (partly overlapping) cortical regions. In this view, visual pictorial imagery might be crucially dependent on V1, while the parietal area 7 is important for visuospatial imagery. Here, we use both fMRI with rTMS to test the latter prediction. Subjects had to indicate whether a cross-mark, presented in a 4 by 5 grid on a computer screen, would fall on an imagined letter or not. The control task subjects had to indicate whether the cross-mark appeared in the lower or in the upper half of the grid. Subtraction analysis of the individual fMRI data sets revealed right parietal activation and no primary visual cortex activation during spatial imagery in all subjects. Subsequently, eight subjects received rTMS (sham and real) at the occipital pole and over the parietal region (area 7), after which they performed the same imagery task. The results revealed a significant effect only after stimulation of the parietal lobe. These results provide strong evidence for selective parietal mediation of visuospatial mental imagery.