Cerebellar Control of Eye Movements
One of the earliest consensuses reached by cerebellar physiologists is that an intact cerebellum is necessary for optimal motor performance. But how and where motor commands get adjusted to the defies of a perceptual error due to adversities in motor exec
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Pablo M. Bla´zquez and Angel M. Pastor
Abstract
One of the earliest consensuses reached by cerebellar physiologists is that an intact cerebellum is necessary for optimal motor performance. But how and where motor commands get adjusted to the defies of a perceptual error due to adversities in motor execution remains elusive. Oculomotor physiologists have tackled these questions using an exemplar model for motor control, eye movement, and a multifaceted approach consisting of correlation of structure and function, effects of lesions, neuronal recordings, and model simulations. This chapter reviews the literature and provides evidence that the cerebellum exerts control over all types of eye movements and that this control is distributed such that different regions of the cerebellum are more or less specialized in different types of eye movements. In addition to the online control of eye movements, the cerebellum plays a key role in motor learning of eye movements. Unifying theories of motor control built in part thanks to the data presented in this chapter suggest that the cerebellum is part of the neuronal circuit responsible for constructing predictions of the consequences of the motor command signal, prediction that are necessary for fine movement control.
P.M. Bla´zquez (*) Department of Otolaryngology, School of Medicine, Washington University, 4566 Scott Avenue, St. Louis, MO, 63110, USA e-mail: [email protected] A.M. Pastor Departamento de Fisiologı´a, Universidad de Sevilla, 41012 Sevilla, Spain e-mail: [email protected] M. Manto, D.L. Gruol, J.D. Schmahmann, N. Koibuchi, F. Rossi (eds.), 1155 Handbook of the Cerebellum and Cerebellar Disorders, DOI 10.1007/978-94-007-1333-8_49, # Springer Science+Business Media Dordrecht 2013
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P.M. Bla´zquez and A.M. Pastor
Introduction The Irish neurologist Gordon Morgan Holmes examined many First World War survivors with gunshots affecting the occipital region of the brain. These patients had severe problems with balance and voluntary movement execution. As he pointed out, in relation to nystagmus, “this failure of posture is in every way comparable to that present in the rest of the motor system, but exceeds it in degree. The reason of this may be that the cerebellum . . . has intimate anatomical and functional connections with the vestibular apparatus, and the later has a dominant influence on ocular movements and postures” (Holmes 1939). Today, it is known that an intact cerebellum is necessary to properly control all eye movements present to more or less extent in all vertebrates – smooth pursuit, saccades, vestibuloocular reflex (VOR), optokinetic reflex (OKR), and vergence – as well as the systems for gaze maintenance (the velocity storage mechanism and the oculomotor integrator). The function of eye movements is to either compensate for self- or external world movement of the visual scene (vestibular and optokinetic) or to bring and keep foveated a region of interest of the visual scene (saccades and smooth pursuit). Smooth pursuit eye movements are slo
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