Does Inferior-Olive Hypersynchrony Affect Vestibular Heading Perception?

Multisensory integration is critical for resolving ambiguities in isolated sensory systems assuring accurate perception of one's own linear motion, i.e., heading. The vestibular signal, a critical source of information for heading perception, is transformed in appropriate coordinates suitable for multisensory integration-such transformation takes place under cerebellar supervision. Deficiency in cerebellar function due to Purkinje cell loss results in inaccurate multisensory integration and impaired heading perception. Here, we predict that a classic movement disorder, the syndrome of oculopalatal tremor (OPT), also presents with inaccurate heading direction perception. The characteristic feature of oculopalatal tremor is pseudohypertrophic inferior olive that constantly sends spontaneous, hypersynchronous, abnormal, and meaningless signals to the cerebellum. Such malicious olive signal can impair heading perception. We examined vestibular heading perception in 6 individuals with OPT and 9 age-matched healthy controls (HC). We used a two-alternative forced choice task performed during passive en bloc translation. Compared with age-matched HC, OPT group had significantly higher heading direction perception threshold indicating a less sensitive vestibular system to variations in heading direction. Using computational simulations, we show that the addition of the abnormal noise into the cerebellar system results in decreased spatiotemporal tuning behavior of the cerebellar output. Such impairment in spatiotemporal tuning causes reduced ability to perceive heading direction. Hyperactivity in the inferior-olive cerebellar pathway impairs the heading direction perception. We suggest that this impairment stems from abnormal noise into the cerebellum due to hypersynchronized inferior olive.