Open- and Closed-Loop Microcomplexes in Neocerebellum

Neocerebellum facilitates motor and cognitive behavior via olivocerebellar modules, in which Purkinje cells (PCs), cerebellar nuclei (CN) neurons and olivary cells are supposed to form exclusively closed-loops. Here, we show that parts of the modules can be organized in an open-loop feedforward fashion where PCs do not contact the CN neurons that provide feedback to the olive. The PCs in the open-loop microcomplexes exclusively target projection CN neurons, through which cerebellum modulates downstream brainstem regions controlling behavior. This novel cerebellar architecture, containing open- and closed-loop microcomplexes within single modules, offers a mechanism by which mossy fiber information can be differentially used either as feedforward control of behavior and/or as feedback to the olivary subnuclei that regulates activity and plasticity within the module involved. This potential for both integrated and segregated regulation of behavior and feedback within single modules enriches the computational repertoire of the olivocerebellar system.