It has been shown previously that
hyperventilation modifies the features of the nystagmus in cerebellar patients (Walker and Zee, 1999). It has been hypothesized that
hyperventilation influences the oculomotor control through a metabolic effect on cerebellar
calcium channels, which play a critical role in the firing behaviour of neuronal populations in the cerebellum. This hypothesis has been tested here by analysing fast goal-directed limb movements before and after
hyperventilation in
spinocerebellar ataxia type 6 (SCA-6), a disease associated with a
polyglutamine expansion in the alpha 1-A
voltage-dependent calcium channel. Cerebellar
hypermetria associated with fast distal single-joint movements was found to be increased following
hyperventilation in patients presenting SCA-6 but remained unchanged in patients with idiopathic late-onset cerebellar degeneration (ILOCA). This is a new provocative test to enhance distal
dysmetria in SCA-6. The present results strengthen the hypothesis of Walker and Zee. It is suggested that
hyperventilation enhances the defective
calcium transfers in SCA-6, resulting in an impairment of the
calcium influx in particular into Purkinje cells involved in the control of fast goal-directed voluntary movements.