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Cerebellar Motor Learning: When Is Cortical Plasticity Not Enough?

Porrill, J. and Dean, P. (2007) Cerebellar Motor Learning: When Is Cortical Plasticity Not Enough? PLoS Computational Biology, 3 (10). e197. ISSN 1553-734X

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Abstract

Classical Marr-Albus theories of cerebellar learning employ only cortical sites of plasticity. However, tests of these theories using adaptive calibration of the vestibulo–ocular reflex (VOR) have indicated plasticity in both cerebellar cortex and the brainstem. To resolve this long-standing conflict, we attempted to identify the computational role of the brainstem site, by using an adaptive filter version of the cerebellar microcircuit to model VOR calibration for changes in the oculomotor plant. With only cortical plasticity, introducing a realistic delay in the retinal-slip error signal of 100 ms prevented learning at frequencies higher than 2.5 Hz, although the VOR itself is accurate up to at least 25 Hz. However, the introduction of an additional brainstem site of plasticity, driven by the correlation between cerebellar and vestibular inputs, overcame the 2.5 Hz limitation and allowed learning of accurate high-frequency gains. This ‘‘cortexfirst’’ learning mechanism is consistent with a wide variety of evidence concerning the role of the flocculus in VOR calibration, and complements rather than replaces the previously proposed ‘‘brainstem-first’’ mechanism that operates when ocular tracking mechanisms are effective. These results (i) describe a process whereby information originally learnt in one area of the brain (cerebellar cortex) can be transferred and expressed in another (brainstem), and (ii) indicate for the first time why a brainstem site of plasticity is actually required by Marr-Albus type models when highfrequency gains must be learned in the presence of error delay.

Item Type: Article
Copyright, Publisher and Additional Information: © 2007 Porrill and Dean. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Department of Psychology (Sheffield)
Depositing User: Sheffield Import
Date Deposited: 27 Oct 2009 16:38
Last Modified: 15 Sep 2014 01:17
Published Version: http://dx.doi.org/10.1371/journal.pcbi.0030197
Status: Published
Publisher: Public Library of Science
Refereed: Yes
Identification Number: doi: 10.1371/journal.pcbi.0030197
URI: http://eprints.whiterose.ac.uk/id/eprint/10036

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