This study compares brain activation patterns evoked by smooth pursuit and by fixation suppression of the optokinetic reflex
(OKR) using similar retinal stimulation. Functional magnetic resonance imaging (fMRI) was performed during smooth pursuit
stimulation in which a moving target was presented on a stationary pattern of stripes, and during fixation suppression of
OKR in which a stationary target was presented on a moving pattern of stripes. All subjects could effectively ignore the background
pattern and were able to keep the target continuously on the fovea with few saccades, in both experiments. Smooth pursuit
evoked activation in the frontal eye fields (FEF), the supplementary eye fields (SEF), the parietal eye fields (PEF), the
motion-sensitive area (MT/V5), and in lobules and vermis VI of the cerebellum (oculomotor areas). Fixation suppression of
OKR induced activation in the FEF, PEF, and MT/V5. The direct comparison analysis revealed more activation in the right lobule
VI of the cerebellum and in the right lingual and calcarine gyri during smooth pursuit than during fixation suppression of
OKR. Using similar retinal stimulation, our results show that smooth pursuit and fixation suppression of the OKR appear to
activate largely overlapping pathways. The increased activity in the oculomotor areas of the cerebellum during smooth pursuit
is probably due to the presence of an active eye movement component.
Keywords Optokinetic reflex (OKR) - Smooth pursuit (SP) - Functional magnetic resonance imaging (fMRI) - Fixation