The Three Cornerstones of Cerebellar Ataxia: Closing the Loop of 200 Years of Cerebellar Research

From a nosological standpoint, the terminology of cerebellar ataxia encompasses now the cerebellar motor syndrome (CMS), the vestibulo-cerebellar syndrome (VCS), and the recently described cerebellar cognitive-affective syndrome (CCAS or Schmahmann’s syndrome) (Manto M, Habas C. (2013). Le cervelet, de l’anatomie et la physiologie à la clinique humaine. Springer; Manto M, Mariën P, Cerebellum & Ataxias, 2:2, 2015). After two centuries of research focusing on motor deficits, cerebellar ataxiology now extends beyond postural and gait disturbances, limb incoordination, speech motor deficits, and oculomotor deficits, gathering also deficits of cognitive/affective operations observed in Schmahmann’s syndrome (Schmahmann JD, Sherman J, Brain: A Journal of Neurology, 12:561–579, 1988; Manto M, Mariën P, Cerebellum & Ataxias, 2:2, 2015). In this chapter, we review the historical background of ataxiology and current neuroanatomical, electrophysiological, neuroimaging, and clinical evidences which allow to attest the role of the cerebellum in three essential functions: the regulation of limb motor control (involved in CMS), the regulation of ocular movements (involved in VCS), and the regulation of cognitive/affective functions (involved in CCAS/Schmahmann’s syndrome). This new conceptualization of clinical ataxiology into three cornerstones has major impacts from preclinical studies to daily clinical applications in cerebellar disorders.