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Directional asymmetry in vertical smooth-pursuit and cancellation of the vertical vestibulo-ocular reflex in juvenile monkeys

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Please use this identifier to cite or link to this item:http://hdl.handle.net/2115/30145

Title: Directional asymmetry in vertical smooth-pursuit and cancellation of the vertical vestibulo-ocular reflex in juvenile monkeys
Authors: Akao, Teppei Browse this author
Kumakura, Yousuke Browse this author
Kurkin, Sergei Browse this author
Fukushima, Junko Browse this author
Fukushima, Kikuro Browse this author
Keywords: Smooth-pursuit
Vestibular system
VOR cancellation
Gain
Directional asymmetry
Training
Juvenile macaque
Cerebellar flocculus
Issue Date: Oct-2007
Publisher: Springer Berlin / Heidelberg
Journal Title: Experimental Brain Research
Volume: 182
Issue: 4
Start Page: 469
End Page: 478
Publisher DOI: 10.1007/s00221-007-1005-1
Abstract: Young primates exhibit asymmetric eye movements during vertical smooth-pursuit across a textured background such that upward pursuit has low velocity and requires many catch-up saccades. The asymmetric eye movements cannot be explained by the un-suppressed optokinetic reflex resulting from background visual motion across the retina during pursuit, suggesting that the asymmetry reflects most probably, a low gain in upward eye commands (Kasahara et al. in Exp Brain Res 171:306–321, 2006). In this study, we examined (1) whether there are intrinsic differences in the upward and downward pursuit capabilities and (2) how the difficulty in upward pursuit is correlated with the ability of vertical VOR cancellation. Three juvenile macaques that had initially been trained only for horizontal (but not vertical) pursuit were trained for sinusoidal pursuit in the absence of a textured background. In 2 of the 3 macaques, there was a clear asymmetry between upward and downward pursuit gains and in the time course of initial gain increase. In the third macaque, downward pursuit gain was also low. It did not show consistent asymmetry during the initial 2 weeks of training. However, it also exhibited a significant asymmetry after 4 months of training, similar to the other two monkeys. After 6 months of training, these two monkeys (but not the third) still exhibited asymmetry. As target frequency increased in these two monkeys, mean upward eye velocity saturated at ∼15°/s, whereas horizontal and downward eye velocity increased up to ∼40°/s. During cancellation of the VOR induced by upward whole body rotation, downward eye velocity of the residual VOR increased as the stimulus frequency increased. Gain of the residual VOR during upward rotation was significantly higher than that during horizontal and downward rotation. The time course of residual VOR induced by vertical whole body step-rotation during VOR cancellation was predicted by addition of eye velocity during pursuit and VOR x1. These results support our view that the directional asymmetry reflects the difference in the organization of the cerebellar floccular region for upward and downward directions and the preeminent role of pursuit in VOR cancellation.
Rights: The original publication is available at www.springerlink.com
Type: article (author version)
URI: http://hdl.handle.net/2115/30145
Appears in Collections:雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 福島 菊郎

 

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