It is thought that the brain does not simply react to sensory feedback, but rather uses an internal model of the body to predict the consequences of motor commands before sensory feedback arrives. Time-delayed sensory feedback can then be used to correct for the unexpected—perturbations, motor noise, or a moving target. The cerebellum has been implicated in this predictive control process, as cerebellar damage leads to specific deficits in movement control (e.g. poor targeting, oscillation) that are reminiscent of a poorly tuned control system in engineering. It is unknown whether damage to the cerebellum interferes with the ability to use feedback control (i.e. to incorporate information from the sensory system to appropriately adjust their movements in-flight). Here we used behavioral and computational approaches to show that cerebellar patients have an intact feedback control system that is similar to that seen in healthy subjects. We then show that we can use this intact mechanism to improve cerebellar patients’ movement control by altering visual feedback in a virtual reality environment. Finally, we test a debated intervention, the addition of mass to the limbs, in patients with cerebellar damage. Because treatment options for this patient population are currently limited to therapy-based interventions, it is important to understand what control mechanisms remain intact in these patients and whether simple alteration of limb inertia might help resolve symptoms for even a subset of the population. The visual feedback-based intervention provides proof-of-concept that patients’ intact feedback control could be leveraged to reduce the effects of ataxia in this patient population. The mass-based intervention, while effective for a subset of the population for extremely simple tasks, does not show promise for clinical viability.
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