Elucidation of the Role of the Premotor Oculomotor Brainstem Nuclei in the Pathogenesis of Oculomotor Dysfunctions in Huntington's Disease (HD).

The stabilization of the images of objects of the visual world onto the central foveal region of the retina enables a clear and stable view of our environment which is achieved by seven different types of eye movements (Table 6.1) (Leigh and Kennard 2004; Leigh and Zee 2006; Rüb et al. 2008b, 2009). The principal aim of these different types of eye movements is either to stabilize gaze to hold images steadily on the central foveal region of the retina or to shift gaze and bring images of objects of the visual world to the retina's fovea independent of head movements. The eye movements are generated by distinct and widely separated oculomotor circuits, which involve a variety of premotor oculomotor brainstem nuclei and converge at the level of the cranial nerve nuclei concerned with eye movements (i.e., oculomotor, trochlear, and abducens nuclei). The oculomotor functions are traditionally subdivided on the basis of how they aid vision: saccades, smooth pursuits, vergence, vestibulo-ocular reflex, optokinetic nystagmus, fixation, and gaze holding (Table 6.1) (Büttner and Büttner-Ennever 2006; Büttner-Ennever and Horn 1997; Leigh and Kennard 2004; Leigh and Zee 2006; Rüb et al. 2008b, 2009).