Making Sense of Cerebellar Contributions to Perceptual and Motor Adaptation.

The cerebellum is thought to adapt movements to changes in the environment in order to update an implicit understanding of the association between our motor commands and their sensory consequences. This trial-by-trial motor recalibration in response to external perturbations is frequently impaired in people with cerebellar damage. In healthy people, adaptation to motor perturbations is also known to induce a form of sensory perceptual recalibration. For instance, hand-reaching adaptation tasks produce transient changes in the sense of hand position, and walking adaptation tasks can lead to changes in perceived leg speed. Though such motor adaptation tasks are heavily dependent on the cerebellum, it is not yet understood how the cerebellum is associated with these accompanying sensory recalibration processes. Here we asked if the cerebellum is required for the recalibration of leg-speed perception that normally occurs alongside locomotor adaptation, as well as how ataxia severity is related to sensorimotor recalibration deficits in patients with cerebellar damage. Cerebellar patients performed a speed-matching task to assess perception of leg speed before and after walking on a split-belt treadmill, which has two belts driving each leg at a different speed. Healthy participants update their perception of leg speed following split-belt walking such that the "fast" leg during adaptation feels slower afterwards, whereas cerebellar patients have significant deficits in this sensory perceptual recalibration. Furthermore, our analysis demonstrates that ataxia severity is a crucial factor for both the sensory and motor adaptation impairments that affect patients with cerebellar damage.