Visual motion, eye motion, and relative motion: A parametric fMRI study of functional specializations of smooth pursuit eye movement network areas.

The ability to pursue moving objects with the eyes is vital to humans. However, it remains unclear how the brain differentiates visual object motion, smooth pursuit eye movements (SPEM), and eye movement-induced relative motion on the retina and where visual-to-oculomotor transformation takes place. To characterize functional differences of SPEM-processing cortical areas, we simultaneously measured functional magnetic resonance imaging (fMRI) and smooth pursuit to visual, oculomotor, and visuo-oculomotor stimuli varying the quantity of background dots of the stimuli. Resulting activations involved the whole visuo-oculomotor network. They varied among regions depending on the functional tasks and parametric changes of the background. Activation in many SPEM regions increased from 1 to 16 background dots but decreased at 36 dots. This could be an effect of coherent-texture perception. Putative MST area was not influenced by the amount of moving or stationary background dots. It probably participates in visuo-oculomotor transformation. Parts of the posterior parietal cortex seem specifically activated with relative motion between eye and background, but not with motion per se. This could be important for the perception of spatial references.