Sensorimotor Transformations for Postural Control in the Vermis of the Cerebellum.

The cerebellar vermis plays an essential role in maintaining posture and balance by integrating sensory inputs from multiple modalities to effectively coordinate movement. By transforming convergent sensory information into precise motor commands, it ensures smooth, adaptive motor control, enabling the body to maintain stability in dynamic environments. This review examines recent findings that investigate the distinct neural computations performed by the anterior vermis and posterior vermis (nodulus/uvula). Specifically, we examine how Purkinje cells in these regions integrate vestibular and proprioceptive signals to convert self-motion information from a head-centered to a body-centered reference frame, which is essential for maintaining precise postural control in response to unexpected movements. Additionally, we consider recent findings showing that, during voluntary self-motion, Purkinje cells in the anterior vermis selectively suppress responses in the vestibulospinal pathway by integrating motor inputs with sensory signals. Given the anterior vermis's role in maintaining balance during voluntary behaviors such as locomotion, its suppression prevents counterproductive stabilizing reflexes, enabling goal-directed movement through space. In contrast, the posterior vermis, encompassing the nodulus and uvula, integrates vestibular inputs from both the otoliths and semicircular canals to maintain equilibrium relative to gravitational forces. We thus hypothesize that Purkinje cells in the nodulus/uvula do not generate suppression signals like those observed in the anterior vermis but instead continuously compute our orientation in space, regardless of whether movement is voluntarily generated or unexpected. If our hypothesis is correct, the nodulus/uvula would effectively provide consistent "ground truth" information about self-motion relative to gravity.