Functional magnetic resonance imaging activations of cortical eye fields during saccades, smooth pursuit, and optokinetic nystagmus.

Saccades, smooth pursuit, and optokinetic nystagmus (OKN) are three basic eye movements in our ocular motor repertoire that enable us to explore the visual field. These eye movements are cortically controlled in different cortical eye fields, including the frontal eye fields (FEF) and parietal eye fields (PEF), as well as the motion-sensitive visual area MT+/V5. It is not known if this cortical control is organized in parallel cortico-cortical networks or in adjacent subregions of one system. Nor do we know where the specific eye fields are exactly located. Functional magnetic resonance imaging (fMRI) was used to investigate these open questions about the FEF, PEF, and MT+/V5. Activations of the cortical network of eye-movement control were found in the frontal, parietal, and occipital cortex. While the activation pattern for OKN was not a combination of the patterns for saccades and smooth pursuit, the results suggest that cortical control of OKN occurs in a network parallel to that of saccades and smooth pursuit. Furthermore, a division of the FEF and the PEF into two parts was confirmed for the three ocular motor tasks, as well as a division within each of the three paradigms. MT+/V5 showed two partitions only for saccades, but not for smooth pursuit or OKN.