Little whispers in time: Review of the cerebellar unipolar brush cell, with insights for schizophrenia

The unipolar brush cell (UBC) is a small, variably occurring, and originally overlooked interneuron of the cerebellum, and is currently emerging as an interesting candidate for effecting sophisticated signal transformations and temporal processing in the cerebellar microcircuit. Although dwarfed in number by the abundance of granule cells in the granular layer, and largely restricted to the flocculonodular complex in rodents, it has undergone considerable evolutionary enrichment through higher species. However, how the UBC may be involved in the recently described higher cognitive, affective and social functions of the cerebellum remains largely unknown. This scoping review covers the last five years of research into the UBC, comprising 31 articles. Original research and review articles from two databases (PubMed and Embase) were included. Articles were grouped into eight themes: Plasticity, Sensory Processing, Neurotransmission, Continuum of Firing Patterns, Neurocircuitry, Experimental Models, Neurodevelopment, and Tumourigenesis. Two papers were review articles. The majority of original research involved rodents, and eleven involved humans. Notable research findings include the description of a continuum of UBC firing patterns, which underpins a powerful array of signal transformations, and the identification of the origins of group 4 medulloblastoma. A brief discussion of the research findings on the UBC, and the implications for schizophrenia is provided. Considering that the cerebellum has a role in higher cognitive functions, and that UBCs are most enriched in the primate brain, with potential roles in timing, auditory processing, sensory prediction and self-cancellation, advances in UBC research may provide novel insights for schizophrenia research.