Fig. 1

Neural circuitry involved in the generation of visually guided saccades. The frontal eye field (FEF) and parietal eye field (PEF) both send projections to the superior colliculus (SC), which in turn directly communicates with omniopause neurons (OPN) in the midline pons. The FEF also projects to the nucleus reticularis tegmenti pontis (NRTP) in the midbrain. This projects to the oculomotor vermis in the cerebellar cortex, which sends inhibitory fibers to the deep cerebellar fastigial oculomotor (FOR) nucleus. The FOR also communicates with OPN. The OPN is responsible for tonic inhibition of excitatory (E) and inhibitory (I) burst neurons, which results in steady fixation of gaze. When the OPN is inhibited during saccade generation, the excitatory and inhibitory burst neurons fire more rapidly. Excitatory burst neurons synapse on the abducens motoneurons (mn) and internuclear neurons (in) in the ipsilateral abducens nucleus. The internuclear neurons of the side receiving excitatory input project to the contralateral abducens motoneuronsmedial rectus subgroup of the oculomotor nucleus. Ipsilateral inhibitory burst neurons project to the contralateral abducens which inhibits movement of the opposing muscles. This results in the rapid, coordinated movement of gaze to a target object