Ocular Motor Disorders Caused by Lesions in the Cerebellum

Abstract

The vestibulocerebellum consists of the flocculus, ventral paraflocculus, nodulus, and uvula. ■ The flocculus receives inputs from the vestibular nucleus and nerve, nucleus prepositus hypoglossi (NPH), inferior olivary nucleus, cell groups of the paramedian tracts (PMT), nucleus reticularis tegmenti pontis (NRTP), and mesencephalic reticular formation. ■ The ventral paraflocculus receives inputs from contralateral pontine nuclei. ■ Project to ipsilateral superior and medial vestibular nuclei, and the y-group ■ Receive input from the medial and inferior vestibular nuclei, vestibular nerve, NPH, and inferior olivary nucleus ■ Project to the vestibular nuclei ■ The oculomotor vermis consists of parts of the declive, folium, tuber, and pyramis. ■ Receives inputs from the inferior olivary nucleus, vestibular nuclei, NPH, paramedian pontine reticular formation (PPRF), NRTP, and dorsolateral and dorsomedial pontine nuclei ■ Projects to the caudal fastigial nucleus ■ Stimulation of the Purkinje cells in the dorsal vermis elicits contralaterally directed saccades and smooth pursuit ■ Receives inputs from the dorsal vermis, inferior olivary nucleus, and NRTP ■ Decussates and projects via the uncinate fasciculus of the brachium conjunctivum to the contralateral PPRF, rostral interstitial nucleus of the medial longitudinal fasciculus, nucleus of the posterior commissure, omnipause neurons in nucleus raphe interpositus, the mesencephalic reticular formation, and superior colliculus ■ Neurons in the fastigial oculomotor region (FOR) fire during both ipsilateral and contralateral saccades. 1. The contralateral FOR neurons burst before the onset of saccade, and the onset of firing is not correlated with any property of the saccade. 2. Conversely, the time of onset for neurons in the ipsilateral FOR varies, with bursts occurring later for larger saccades. 3. Thus, the difference in time of onset between contralateral and ipsilateral FOR activity encodes the amplitude of saccades (i.e., the larger the difference in time of onset, the larger the saccade amplitude). Eye movement abnormalities in uncinate fasciculus lesion include hypometric ipsilesional saccades and hypermetric contralesional saccades (“contrapulsion”). Arnold-Chiari malformation is a malformation of the medullary–spinal junction with herniation of intracranial contents through the foramen magnum. The three types are illustrated in the figure below.