Excitation and Excitability of Unipolar Brush Cells

Abstract

The cerebellum is a distinct brain structure that ensures the spatial accuracy and temporal coordination of movements. It is located superimposed on the brainstem and has an appearance and organization unlike that of the cerebral cortex: its surface has a highly regular foliation pattern, and its neural circuitry is organized in repeated structured modules. Neural activity enters the cerebellum via two excitatory pathways, the mossy ber system and the climbing ber system. Climbing bers originate from the inferior olivary nucleus in the brainstem, and assert a powerful in uence on cerebellar output and long-term adaptation processes. Mossy bers originate from a large number of sources, and carry contextual information on sensory inputs, aspects of motor planning and commands, and proprioceptive feedback. In the cerebellum this information is evaluated and integrated, to produce neural output that in uences ongoing movement directly. Mossy ber signals are processed in the cerebellum in three stages. In the granular layer, the input stage of the cerebellum, mossy ber signals undergo a recoding step where they are combined and expanded by granule cells. Next, in the molecular layer, granule cell signals are integrated with climbing ber signals in Purkinje cells. Together, the granular layer and molecular layer make up the cerebellar cortex. Finally, Purkinje cell activity is integrated in the cerebellar nuclei, which form the output stage, and project to various motor and pre-motor systems in the cerebral cortex and brainstem. The cerebellar cortex acts to modulate ongoing movement commands in order to make movements more accurate. Damage to the cerebellum can cause impairments in the control of movements, and bodily balance and posture.