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Dynamic associations in the cerebellar-motoneuron network during motor learning

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2009-08-26
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Society for Neuroscience
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We assessed here true causal directionalities in cerebellar–motoneuron (MN) network associations during the classical conditioning of eyelid responses. For this, the firing activities of identified facial MNs and cerebellar interpositus (IP) nucleus neurons were recorded during the acquisition of this type of associative learning in alert behaving cats. Simultaneously, the eyelid conditioned response (CR) and the EMG activity of the orbicularis oculi (OO) muscle were recorded. Nonlinear association analysis and time-dependent causality method allowed us to determine the asymmetry, time delays, direction in coupling, and functional interdependences between neuronal recordings and learned motor responses.Weconcluded that the functional nonlinear association between the IP neurons and OO muscle activities was bidirectional and asymmetric, and the time delays in the two directions of coupling always lagged the start of the CR. Additionally, the strength of coupling depended inversely on the level of expression of eyeblink CRs, whereas causal inferences were significantly dependent on the phase information status. In contrast, the functional association between OO MNs and OO muscle activities was unidirectional and quasisymmetric, and the time delays in coupling were always of opposed signs. Moreover, information transfer in cerebellar–MN network associations during the learning process required a “driving common source” that induced the mere “modulating coupling” of the IP nucleus with the final common pathway for the eyelid motor system. Thus, it can be proposed that the cerebellum is always looking back and reevaluating its own function, using the information acquired in the process, to play a modulating-reinforcing role in motor learning.
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En este trabajo profundizamos en el estudio del cerebelo por ser éste el centro nervioso que permite dar continuidad, suavidad y armonía a nuestros movimientos. En general, la perfección de los movimientos se debe a un buen funcionamiento del cerebelo que coordina las órdenes motoras procedentes de la corteza cerebral. Aquí se demuestra que el control dinámico del proceso de aprendizaje motor se sustenta en la determinación del orden temporal (causalidad) y de las interdependencias funcionales entre el cerebelo y las motoneuronas en la vía motora final común. La aproximación analítico-experimental desarrollada para este trabajo permitió demostrar que la transferencia de información en el circuito “cerebelo-motoneuronas” requiere de una “fuente común generadora”, siendo la corteza motora cerebral una fuente bastante plausible en este proceso. Nuestros resultados sugieren que dicha fuente es la que induce un acoplamiento por modulación de fase entre las neuronas tipo A del núcleo interpósito posterior del cerebelo y las motoneuronas del orbicularis oculi en la vía motora final común para las respuestas condicionadas. El artículo también explica por qué la actividad del cerebelo permanece “silente” durante la generación y/o inicio de las respuestas condicionadas.
Proyectos de investigación MICINN-BFU2008-00899/BFI BIO122/CVI-2487
Bibliographic reference
Journal of Neuroscience, vol. 29, nº 34, p. 10750-10763
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