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PubMed1995

On associative motor learning by the cerebellar cortex: from Purkinje unit to network with variational learning rules.

This paper is an attempt to describe the ability of the cerebellar cortical network to coordinate movement on the basis of the continuous behavior of individual neural networks, the so-called "Purkinje units." The problem is considered from the point of view of a hierarchical network with two levels of organization: the level of Purkinje units including Purkinje, star and basket cells, and the level of granule cells and Golgi cells which is a network with a specific architecture. We suggest that the coordination of movements is based on a new class of learning rules between Purkinje units, called variational learning rules (VLR), which are mathematically deduced from the dynamics of a Purkinje unit. This network is driven by two functions H0 and H, defined for each Purkinje unit, which depend on external signals for this unit. Specifically, the proposed interpretation of the coordination of movement depends on three main features: (i) The definition of a unit of function, the Purkinje unit, made up of a Purkinje cell and closely associated cells and connections; (ii) a new learning rule called the "Variational Learning Rule" (VLR), operating at the level of the Purkinje units; (iii) the interpretation of the coordination of movements in terms of excitatory and inhibitory interactions between Purkinje units. An emergent property of the model is that Purkinje units occur in groups which act in opposition in the sense that when the output of one group increases, that of the other decreases.

Association Learning↗
PubMed2006

Reorganization of the rat cerebellar cortex during postnatal development following cisplatin treatment.

We examined the effects of the antitumor agent cisplatin on the development and plasticity of cerebellar cytoarchitecture. Since knowledge of the parallel and climbing fiber-Purkinje cell system is important in order to determine the architectural basis of cerebellar function, we used immunofluorescence for vesicular glutamate transporters (VGluT1 and VGluT2) to evaluate the trend of synaptogenesis of parallel and climbing fibers on Purkinje cells in the cerebellum vermis after a single injection of cisplatin to 10-day-old rats, i.e., during a crucial period of cerebellar development. The temporal and spatial patterns of VGluT1 and VGluT2 immunoreactivity after the early cisplatin injury provided evidence that remodeling of excitatory afferents and Purkinje cell dendrites occurs. After an early slow down of Purkinje cell dendrite growth, 7 days following the treatment, the extension of the molecular layer was reduced, as was parallel fiber innervation, but VGluT1 immunoreactive fibers contacted Purkinje cell dendrite branches extending within the external granular layer. VGluT2 immunopositive climbing fiber varicosities were still largely present on the soma and stem dendrites of Purkinje cells. Twenty days after the cisplatin injection, the thickness of the VGluT1 immunopositive molecular layer was reduced. VGluT2 climbing fiber varicosities were found on the remodeled Purkinje cell dendrites, as in controls, although at a lower density. Alterations in the immunoreactivity for polysialic acid neural cell adhesion molecule (PSA-NCAM) during the recovery phase suggest that this molecule plays a fundamental role not only during development, but also in the reorganization of neuroarchitecture. The changes were restricted to the neocerebellar vermis and were likely dependent on the different timing of lobule formation. The results of these investigations reveal the existence of vulnerability windows of the cerebellum to exposure to experimental or environmental cytotoxic agents during a critical period in development.

Animals↗