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• Frequency selective VOR motor learning was confirmed in goldfish as in other model species. • Sharper tuning of frequency selectivity was found in VOR gain-up than gain-down. • Frequency competitive VOR motor learning was possible in goldfish as in primates. • The cerebellum was shown to be necessary for frequency competitive VOR motor learning. • Purkinje cell activities changed with gain-down but not with gain-up during frequency competitive VOR motor learning. Biological motions commonly contain multiple frequency components in which each fundamental has to be adjusted by motor learning to acquire a new motor skill or maintain acquired skills. At times during this motor performance one frequency component needs to be enhanced (gain-up) while another is suppressed (gain-down). This pattern of simultaneous gain-up and -down adjustments at different frequencies is called frequency competitive motor learning. Currently we investigated cerebellar roles in this behavior utilizing the goldfish vestibulo-ocular reflex (VOR). Previously, VOR motor learning was shown in primates to be frequency selective and exhibit frequency competitive motor learning. Here we demonstrate that the goldfish VOR performs frequency competitive motor learning when high and low frequency components are trained to gain-up and gain-down, respectively. However, when the two frequency components were trained in the opposite directions only gain-up component was observed. We also found that cerebellectomy precluded any frequency competitive VOR motor learning. Complementary single unit recordings from vestibulo-cerebellar Purkinje cells revealed changes in firing modulation along with gain-down learning, but not with gain-up learning irrespective of frequency. These results demonstrate that the cerebellum is required for all frequency competitive VOR motor learning and Purkinje cell activity therein is well correlated with all gain-down behaviors independent of frequency. However, frequency competitive gain-up learning requires intact, recursive brainstem/cerebellar pathways. Collectively these findings support the idea that VOR gain-up and gain-down learning utilize separate brainstem/cerebellar circuitry that, in turn, clearly underlies the unique ability of the oculomotor system to deal with multiple frequency components. [ABSTRACT FROM AUTHOR]

Abstract: Internal models are a key feature of most modern theories of motor control. Yet, it has been challenging to localize internal models in the brain, or to demonstrate that they are more than a metaphor. In the present review, I consider a large body of data on the cerebellar floccular complex, asking whether floccular output has features that would be expected of the output from internal models. I argue that the simple spike firing rates of a single group of floccular Purkinje cells could reflect the output of three different internal models. (1) An eye velocity positive feedback pathway through the floccular complex provides neural inertia for smooth pursuit eye movements, and appears to operate as a model of the inertia of real-world objects. (2) The floccular complex processes and combines input signals so that the dynamics of its average simple spike output are appropriate for the dynamics of the downstream brainstem circuits and eyeball. If we consider the brainstem circuits and eyeball as a more broadly conceived “oculomotor plant,” then the output from the floccular complex could be the manifestation of an inverse model of “plant” dynamics. (3) Floccular output reflects an internal model of the physics of the orbit where head and eye motion sum to produce gaze motion. The effects of learning on floccular output suggest that it is modeling the interaction of the visually-guided and vestibular-driven components of eye and gaze motion. Perhaps the insights from studying oculomotor control provide groundwork to guide the analysis of internal models for a wide variety of cerebellar behaviors. [Copyright &y& Elsevier]

Much literature has studied the relationship between the organization of neurons in the flocculus/ventral paraflocculus and vestibulo-ocular reflex pathways. Although activation of a flocculus central zone produces ipsilateral horizontal eye movement, anatomical tracing evidence in rats suggests that there may not be a simple one-to-one correspondence between flocculus/ventral paraflocculus zones and control of single extraocular muscles or coplanar pairs of antagonistic extraocular muscles. This study used the retrograde transynaptic transport of pseudorabies virus to identify the topographical organization of Purkinje cells in the flocculus/ventral paraflocculus that control the lateral rectus (LR) and medial rectus (MR) muscles in rats. A survival time of 80 h and 84 h was necessary to observe consistent transynaptically labeled cells in the flocculus/ventral paraflocculus following injections of pseudorabies virus into the MR and LR, respectively. The organization of Purkinje cells in the dorsal flocculus and ventral paraflocculus abided by the traditional boundaries, whereas the labeling pattern in the ventral flocculus showed a more complex, interdigitated arrangement. In agreement with prior studies, transynaptically labeled neurons were also observed in specific vestibular nuclear regions within the medial and superior vestibular nuclei and dorsal Y group. The distribution of labeled neurons in ipsilateral and contralateral vestibular nuclei was associated with features of ipsilateral and contralateral retrograde labeling of Purkinje cells in flocculus/ventral paraflocculus. Importantly, this study provides the first evidence of vestibulo-cerebellar zones controlling individual extraocular muscles and also overlapping distribution of neurons in flocculo-vestibular zones that influence the LR and MR motoneuron pools. This suggests that some of these neurons may be responsible for controlling both muscles. [Copyright &y& Elsevier]