Cortical and sub-cortical control of saccades and clinical application.

Saccades allow object of interest that are perceived by the peripheral retina to be displayed on the fovea, a small central retinal area of maximum visual accuracy. Saccades may be generated under a large variety of circumstances, from reflexive like saccades (e.g. towards a threatening visual cue) to highly volitional saccades (e.g. towards the memorized location of a no longer present visual cue). These different contexts correspond to different complexities of decision-making processes and, on a behavioral aspect, to saccades with different latencies, and to the involvement of different cortical areas. However, whatever their type, saccades need to be fast, in order to avoid any persaccadic visual blur, and accurate since the fovea represents less than 1° of visual angle. This combination of accuracy and velocity is achieved thanks to a collaboration of brainstem and cerebellar oculomotor structures. The basic neural structures involved in these processes are reviewed, a special emphasis being given to clinically relevant mechanisms.