Graded functional activation in the visuospatial system with the amount oftask demand

Two studies examined how the amount and type of computational demand are re lated to fMRI-measured activation in three bilateral cortical regions invol ved in the Shepard-Metzler (1971) mental-rotation paradigm. The amount of d emand for the computation of visuospatial coordinates was manipulated by pr esenting mental rotation problems with increasing angular disparity (0, 40, 80, or 120 degrees). Activation in both the left and right intraparietal s ulcal regions increased linearly with angular disparity in two separate stu dies. Activation also occurred in the fusiform gyrus and inferior temporal regions, regions that are primarily associated with the processes of object and object-part identification. By contrast, the demand for object recogni tion and rotation processes was relatively low, and the demand for executin g saccades was high in a control condition that required making a systemati c visual scan of two grids. The grid-scanning condition resulted in relativ ely less activation in the parietal and inferior temporal regions but consi derable activation in frontal areas that are associated with planning and e xecuting saccades, including the precentral gyrus and sulcus into the poste rior middle frontal region. These data suggest that the amount of activatio n in the various cortical regions that support visuospatial processing is r elated to the amount, as well as to the type, of computational demand.