Figure 1. . Major cortical areas involved in control of eye movements and visual processing, with projections illustrating saccade generation in black.

Major cortical areas involved in control of eye movements and visual processing, with projections illustrating saccade generation in black. Saccades are initiated by signals sent from the frontal, parietal or supplementary eye fields to the superior colliculus, which then projects to the brainstem gaze centers. In parallel, the FEF also initiates saccades via direct connections to the BGC. In the indirect pathway, the substantia nigra pars reticulata inhibits the superior colliculus, preventing saccade generation. To turn off this inhibition, the FEFs are activated prior to a saccade, which then inhibits the substantia nigra pars reticulata via the caudate. The saccade pathways are a multidistributed network, but the FEF primarily generates voluntary- or memory-guided saccades, the parietal eye field – reflexive saccades, the SEF – saccades in coordination with body movements as well as successive saccades and the DLPC – antisaccades, the inhibition of reflexive saccades and the advanced planning of saccades. Cerebellar projections (shown in blue) fine-tune the saccades, given that cerebellar lesions can lead to saccadic dysmetria. The nucleus reticularis tegmenti pontis receives projections from the FEF and the superior colliculus (projection not shown) and in turn projects to the cerebellar ocular V. The Vinhibits the ipsilateral caudal fastigial nucleus, which then projects to the BGC to enhance saccades moving to the contralateral side and tamp down saccades moving to the ipsilateral side, likely via both inhibitory and excitatory connections [33,70,71].

BGC: Brainstem gaze centers; CN: Caudate; DLPC: Dorsolateral prefrontal cortex; FEF: Frontal eye field; FN: Fastigial nucleus; NRTP: Nucleus reticularis tegmenti pontis; PEF: Parietal eye fields; SC: Superior colliculus; SEF: Supplementary eye field; SNPR: Substantia nigra pars reticulata; V: Vermis.