Rollvection versus linearvection: comparison of brain activations in PET

We conducted a PET study to directly compare the differential effects of visual motion stimulation that induced either rollvection about the line of sight or forward linearvection along this axis in the same subjects. The main question was, whether the areas that respond to vection are identical or separate and distinct for rollvection and linearvection. Eleven healthy volunteers were exposed to large-field (100 degrees x 60 degrees ) visual motion stimulation consisting of (1) dots accelerating from a focus of expansion to the edge of the screen (forward linearvection) and (2) dots rotating counterclockwise in the frontal plane (clockwise rollvection). These two stimuli, which induced apparent self-motion in all subjects, were compared to each other and to a stationary visual pattern. Linearvection and rollvection led to bilateral activations of visual areas including medial parieto-occipital (PO), occipito-temporal (MT/V5), and ventral occipital (fusiform gyri) cortical areas, as well as superior parietal sites. Activations in the polar visual cortex around the calcarine sulcus (BA 17, BA 18) were larger and more significant during linearvection. Temporo-parietal sites displayed higher activity levels during rollvection. Differential activation of PO or MT/V5 was not found. Both stimuli led to simultaneous deactivations of retroinsular regions (more pronounced during linearvection); this is compatible with an inhibitory interaction between the visual and the vestibular systems for motion perception.