Functional Units of Cerebellar Information Processing: Zones, Microzones And Microcomplexes
Dept of Experimental Medical Science, Lund University, Sweden
With respect to functional organization, the cerebellar olivo-cortico-nuclear network controlling rubro- and corticospinal tracts via nucleus interpositus anterior (NIA) is one of the best characterized mammalian motor systems involved in limb movement control. Here, the conceptual framework for dividing the NIA system into functional units at different levels of resolution, such as zones, microzones and microcomplexes will be discussed. The physiological and anatomical basis for the compartmentalization as well as the methodologies used to determine the organization of microzones, interactions between the climbing fibre and mossy fibre systems as revealed by receptive field organization of Purkinje cells and interneurons, the corticonuclear projection and the nucleofugal output will be critically assessed. The second part of the talk will focus on recent findings indicating that climbing fibres innervating microcomplexes of the NIA system mediate highly integrated sensorimotor information derived from spinal nociceptive withdrawal reflex modules. Following a brief account of how the spinal withdrawal reflex system operates the implications of the relationship between spinal modules and microcomplexes of the NIA system for cerebellar sensorimotor processing will be outlined. It will be argued that spinal ‘pre-processing’ of climbing fibre input constitutes a signal conversion from ‘sensory’ to ‘motor’ coordinates, providing individual microcomplexes with motor error signals relevant to the action of single limb muscles. Taken together, the findings should prove useful for conceptual and computational models of cerebellar sensorimotor processing underlying motor control, adaptation and learning.