Pitch discrimination in cerebellar patients: evidence for a sensory deficit

In the last two decades, a growing body of research showing cerebellar involvement in an increasing number of nonmotor tasks and systems has prompted an expansion of speculations concerning the function of the cerebellum. Here, we tested the predictions of a hypothesis positing cerebellar involvement in sensory data acquisition. Specifically, we examined the effect of global cerebellar degeneration on primary auditory sensory function by means of a pitch discrimination task. The just noticeable difference in pitch between two tones was measured in 15 healthy controls and in 15 high functioning patients afflicted with varying degrees of global cerebellar degeneration caused by hereditary, idiopathic, paraneoplastic, or postinfectious pancerebellitis. Participants also performed an auditory detection task assessing sustained attention, a test of verbal auditory working memory, and an audiometric test. Patient pitch discrimination thresholds were on average five and a half times those of controls and were proportional to the degree of cerebellar ataxia assessed independently. Patients and controls showed normal hearing thresholds and similar performance in control tasks in sustained attention and verbal auditory working memory. These results suggest there is an effect of cerebellar degeneration on primary auditory function. The findings are consistent with other recent demonstrations of cerebellar-related sensory impairments, and with robust cerebellar auditorily evoked activity, confirmed by quantitative meta-analysis, across a range of functional neuroimaging studies dissociated from attention, motor, affective, and cognitive variables. The data are interpreted in the context of a sensory hypothesis of cerebellar function.