Cerebellum: Evolution and comparative anatomy
The vertebrate cerebellum is similar in cellular organization and connections in all vertebrates. The cerebellum receives sensory input from the spinal cord, midbrain, and forebrain and a corollary discharge when a movement is made. The output of the cerebellum is focused on the main motor pathways. Lesions of the cerebellum produce deficits in movement and an inability to modify open loop reflexes and other forms of motor learning. The similarity of the cortical circuitry in different vertebrates and the differences in its spatial organization and the resulting gross morphology of the cerebellum are considered in this article. The plasticity of the cerebellar circuitry and its role in motor learning is emphasized as a main factor in its preservation. The development of this circuitry and of the longitudinal zonal architecture of the cerebellum in mammals, birds, and reptiles is recapitulated to highlight possible locations where evolutionary changes in the cerebellum may have occurred.