REVIEW Motor learning in the VOR: the cerebellar component Dianne M. Broussard • Heather K. Titley • Jordan Antflick • David R. Hampson Received: 20 October 2010 / Accepted: 31 January 2011 / Published online: 19 February 2011 Ó Springer-Verlag 2011 Abstract This paper reviews results that support a model in which memory for VOR gain is initially encoded in the flocculus, and in which cerebellar LTD and LTP are responsible for gain increases and gain decreases, respec- tively. We also review data suggesting that after it is encoded, motor memory can either be disrupted, possibly by a local mechanism, or else consolidated. We show that consolidation can be rapid, in which case the frequency dependence of learning is unchanged and we will argue that this is consistent with a local mechanism of consoli- dation. In the longer term, however, the available evidence supports the transfer of memory out of the flocculus. In new experiments reported here, we address the mechanism of memory encoding. Pharmacological evidence shows that both mGluR1 and GABA B receptors in the flocculus are necessary for gain-up, but not for gain-down learning. Immunohistochemical experiments show that the two receptors are largely segregated on different dendritic spines on Purkinje cells. Together with what is already known of the mechanisms of cerebellar LTD and LTP, our data suggest that the direction of learning may be deter- mined by interactions among groups of spines. Our results also provide new evidence for the existence of frequency channels for vestibular signals within the cerebellar cortex. Keywords Cerebellum Á Learning Á Vestibulo-ocular reflex Á Vestibular Á LTD Á LTP The vestibulo-ocular reflex (VOR) pathway is perhaps the most thoroughly studied of all vestibular pathways, and its response to horizontal rotatory head movements has been the focus of the most attention. The VOR stabilizes gaze during head movements, making it possible to move and see at the same time. The sensory input driving the VOR is exclusively vestibular. This means that the reflex can respond rapidly to head velocity and acceleration signals. However, the vestibular system does not provide feedback about accurate gaze stabilization; therefore, it is necessary to recalibrate the gain and phase of the VOR’s response to movement whenever conditions change in either the sen- sory or motor periphery. The gain of the VOR can be increased or decreased; phase leads or lags can also be introduced. This recalibration is a simple form of motor learning. Two conditions are sufficient to cause learning in the VOR: head movement and a visual error signal. Unlike the immediate modulation of VOR gain by VOR cancellation or enhancement, learning causes changes that are expressed when the VOR gain is measured in darkness. Gain increases (gain-up learning) can be induced by having cats wear 29 magnifying lenses during passive rotation, and D. M. Broussard Á H. K. Titley Department of Physiology, University of Toronto, Toronto, Canada D. M. Broussard Division of Neurology, Department of Medicine, University of Toronto, Toronto, Canada D. M. Broussard Toronto Western Research Institute, University Health Network, Toronto, Canada J. Antflick Á D. R. Hampson Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON, Canada D. M. Broussard (&) MP 12-318, Toronto Western Hospital, 399 Bathurst St., Toronto, ON M5T 2S8, Canada e-mail: dianne.m.broussard@gmail.com 123 Exp Brain Res (2011) 210:451–463 DOI 10.1007/s00221-011-2589-z