Fast versus slow: different saccadic behavior in cerebellar ataxias

Spinocerebellar ataxia type 2 (SCA2) is a genetic neurodegenerative disorder primarily characterized by involvement of the brainstem and cerebellum, basal ganglia, spinal cord, cerebral cortex, but white matter is also involved. In late-onset cerebellar ataxia (LOCA), the cerebellum is mainly involved, as demonstrated by clinical and neuroradiological findings. These neurodegenerative diseases are often associated with progressive abnormalities in eye movement control, particularly saccadic changes. We recorded saccadic eye movements in eight SCA2 patients and 10 LOCA patients. Here, we suggest that abnormalities in saccadic parameters differ in the two groups of patients according to specific anatomical substrates. The different saccadic behavior observed in these two clinically distinct degenerative cerebellar diseases offers the opportunity to simplify some general mechanisms of saccadic motor control. Like his mentor Fred Plum, John Leigh strongly encouraged younger neuroscientists to tackle neurological problems by investigating "pathological physiology." With this teaching in mind, we studied patients with rare neurometabolic and neurodegenerative diseases.