Cerebellar zones: history, development, and function.

The longitudinal and transverse zonal arrangement of axonal projections to and from the cerebellum, even more than the well-known laminar cytoarchitecture, is the hallmark of cerebellar anatomy. No model of cerebellar function, whether in motor control, cognition, or emotion, will be complete without understanding the development and function of zones. To this end, a special issue of this journal is dedicated to zones, and the purpose of this article is to summarize the research and review articles that are contained within. The special issue begins by considering some of the very first studies in the 1960s and 1970s that led to our modern understanding of this unique and defining anatomical substructure. Then, it considers the molecular analogs of longitudinal zones in the form of stripes in the cerebellar cortex and related sub-areas in the deep cerebellar nuclei, and it includes studies on the genetic underpinnings of stripes and zones. Several articles address the evolution of both embryonic clusters and adult zones across vertebrate species, and others discuss the functional and clinical relevance of zones. While we do not yet fully understand the role of zones with respect to motor behavior in all of its complexities, cerebellar function is clearly modular, and combinatorial models of complex motor movements based on multi-purpose modules are beginning to emerge. This special issue, by refocusing attention on this fundamental organization of the cerebellum, sets the stage for future studies that will more fully reveal the cellular, developmental, behavioral, and clinical relevance of zones.