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The Cerebellum: Brain for an Implicit Se... > 18. Concluding Thoughts - Pg. Vol4-204

18 Concluding Thoughts 18-1 What Is the Cerebellum in a Nutshell? Neuronal circuits in the cerebellum have now been decomposed to the extent that their various neuronal components are defined and synaptic plasticity (LTD/LTP) is as memory elements in neuronal networks; that is, at least for the early phase of memory processes (Chapters 3­7). Detailed signal flow charts underlying synaptic plasticity have been revealed, as have been some genetic and pharmacological means to manipulate this plasticity. Reconstruction of the cerebellar machine has also advanced markedly (Chapter 9, "Network Models"). Three-layered neuronal networks like a simple perceptron, which is based on the design of neuronal cir- cuits, have been proposed as a model of the cerebellum that is capable of spatial pattern recognition. In addition, adaptive filter models are capable of temporal pattern recognition (Chapter 9). Real cerebellar networks integrate these two capabilities to major extent, and the networks have been simulated using liquid state machine models. Circuits have also been modeled for error learning during repeated attempts to execute a task. Experimentally-based knowledge about neu- ronal networks in the cerebellum has also become increasingly more detailed. For example, Lugaro cells and small inhibitory neurons have been added to the neu- ronal wiring diagram of the cerebellar cortical network, albeit their functional roles are still unclear. Also, many different neuropeptides and amines conveyed by beaded fibers to the cerebellum from the hypothalamus have been identified, and their functional roles are now being considered in terms of neuromodulation. Recently, it has become clear that the cerebellar and vestibular nuclei act as a memory site and as such, are a complement to the memory role of the cerebellar cortex. It will be intriguing to see how this ever-emerging new knowledge will modify and expand our present models of cerebellar function. 204