Cerebellum and gravity: Altered earth’s gravity perception under pathological conditions and response to altered gravity in space

Abstract

Life on Earth has developed under the influence of gravity and remains adapted to unit gravity. As different organisms evolved to survive optimally in water, ground, and air habitats, special adaptive mechanisms developed to deal with gravity. In humans and most land mammals, maintaining postural equilibrium requires constant integration of visual, vestibular, and somatosensory systems to compensate for gravity. The gravity sensors located in the inner ear make connections to the eyes, vestibulocerebellum, and postural muscles. The vestibulocerebellum, due to direct connections with the vestibular gravity receptors, is the primary gravity response center. It is involved in spatial orientation and regulation of gait and, together with the spinocerebellum and pontocerebellum, plays an important role in motor control. Several cerebellar pathologies, including Ataxias and dystonia in humans and animals, are characterized by altered gravity perception and affect posture, gait, and small motor coordination and timing. In space, where the gravitational sense of up and down diminishes, the vestibulocerebellar system must adapt and establish a new way to interpret the altered gravitational environment. This chapter explores cerebellar disorders in the context of altered interactions with Earth’s gravity in humans and animal models and the reaction of astronauts to altered gravity in space (microgravity). This chapter also considers the effects of microgravity and hypergravity on the development of cerebellar structure and function in experimental animals. Understanding how the cerebellum responds to altered gravity should provide insight into the nature of altered gravity perception in various neurological disorders and accelerate the development of therapeutic tools.